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Sampled sound format IFF FORM "SAMP" Sampled Sound Date: Dec 3,1989 From: Jim Fiore and Jeff Glatt, dissidents The form "SAMP" is a file format used to store sampled sound data in some ways like the current standard, "8SVX". Unlike "8SVX", this new format is not restricted to 8 bit sample data. There can be more than one waveform per octave, and the lengths of different waveforms do not have to be factors of 2. In fact, the lengths (waveform size) and playback mapping (which musical notes each waveform will "play") are independently determined for each wave- form. Furthermore, this format takes into account the MIDI sample dump stan- dard (the defacto standard for musical sample storage), while also incorpo- rating the ability to store Amiga specific info (for example, the sample data that might be sent to an audio channel which is modulating another channel). Although this form can be used to store "sound effects" (typically oneShot sounds played at a set pitch), it is primarily intended to correct the many deficiencies of the "8SVX" form in regards to musical sampling. Because the emphasis is on musical sampling, this format relies on the MIDI (Musical Instrument Digital Interface) method of describing "sound events" as does virtually all currently manufactured, musical samplers. In addition, it at- tempts to incorporate features found on many professional music samplers, in anticipation that future Amiga models will implement 16 bit sampling, and thus be able to achieve this level of performance. Because this format is more complex than "8SVX", programming examples to demonstrate the use of this format have been included in both C and assembly. Also, a library of func- tions to read and write SAMP files is available, with example applications. SEMANTICS: When MIDI literature talks about a sample, usually it means a collection of many sample points that make up what we call a "wave". =====SIMILARITIES AND DIFFERENCES FROM THE "8SVX" FORM======= Like "8SVX", this new format uses headers to separate the various sections of the sound file into chunks. Some of the chunks are exactly the same since there wasn't a need to improve them. The chunks that remain unchanged are as follows: "(c) " "AUTH" "ANNO" Since these properties are all described in the original "8SVX" document, please refer to that for a description of these chunks and their uses. Like the "8SVX" form, none of these chunks are required to be in a sound file. If they do appear, they must be padded out to an even number of bytes. Furthermore, two "8SVX" chunks no longer exist as they have been incorpo- rated into the "BODY" chunk. They are: "ATAK" "RLSE" Since each wave can be completely different than the other waves in the sound file (one wave might be middle C on a piano, and another might be a snare drum hit), it is necessary for each wave to have its own envelope de- scription, and name. The major changes from the "8SVX" format are in the "MHDR", "NAME", and "BODY" chunks. =================THE "SAMP" HEADER================ At the very beginning of a sound file is the "SAMP" header. This is used to determine if the disk file is indeed a SAMP sound file. It's attributes are as follows: #define ID_SAMP MakeID('S','A','M','P') In assembly, this looks like: CNOP 0,2 ;word-align SAMP dc.b 'SAMP' sizeOfChunks dc.l [sizes of all subsequent chunks summed] =================THE "MHDR" CHUNK================= The required "MHDR" chunk immediately follows the "SAMP" header and consists of the following components: #define ID_MHDR MakeID('M','H','D','R') /* MHDR size is dependant on the size of the imbedded PlayMap. */ typedef struct{ UBYTE NumOfWaves, /* The number of waves in this file */ Format, /* # of ORIGINAL significant bits from 8-28 */ Flags, /* Various bits indicate various functions */ PlayMode, /* determines play MODE of the PlayMap */ NumOfChans, Pad, PlayMap[128*4], /* a map of which wave numbers to use for each of 128 possible Midi Notes. Default to 4 */ } MHDRChunk; The PlayMap is an array of bytes representing wave numbers. There can be a total of 255 waves in a "SAMP" file. They are numbered from 1 to 255. A wave number of 0 is reserved to indicate "NO WAVE". The Midi Spec 1.0 designates that there are 128 possible note numbers (pitches), 0 to 127. The size of an MHDR's PlayMap is determined by (NumOfChans * 128). For example, if NumOfChans = 4, then an MHDR's PlayMap is 512 bytes. There are 4 bytes in the PlayMap for EACH of the 128 Midi Note numbers. For example, the first 4 bytes in PlayMap pertain to Midi Note #0. Of those 4 bytes, the first byte is the wave number to play back on Amiga audio channel 0. The second byte is the wave number to play back on Amiga audio channel 1, etc. In this way, a single Midi Note Number could simultaneously trigger a sound event on each of the 4 Amiga audio channels. If NumOfChans is 1, then the PlayMap is 128 bytes and each midi note has only 1 byte in the PlayMap. The first byte pertains to midi note #0, the second pertains to midi note #1, etc. In this case, a player program might elect to simply play back the PlayMap wave number on any available amiga audio channel. If NumOfChans = 0, then there is no imbedded PlayMap in the MHDR, no midi note assignments for the waves, and an application should play back waves on any channel at their default sampleRates. In effect, the purpose of the PlayMap array is to determine which (if any) waves are to be played back for each of the 128 possible Midi Note Numbers. Usually, the MHDR's NumOfChans will be set to 4 since the Amiga has 4 audio channels. For the rest of this document, the NumOfChans is assumed to be 4. As mentioned, there can be a total of 255 waves in a "SAMP" file, numbered from 1 to 255. A PlayMap wave number of 0 is reserved to indicate that NO WAVE number should be played back. Consider the following example: The first 4 bytes of PlayMap are 1,3,0,200. If a sample playing program receives (from the serial port or another task perhaps) Midi Note Number 0, the following should occur: 1) The sampler plays back wave 1 on Amiga audio channel number 0 (because the first PlayMap byte is 1). 2) The sampler plays back wave 3 on Amiga audio channel number 1 (because the second PlayMap byte is 3). 3) The sampler does not effect Amiga audio channel 2 in any way (because the third PlayMap byte is a 0). 4) The sampler plays back wave 200 on Amiga audio channel number 4 (because the fourth PlayMap byte is 200). (This assumes INDEPENDANT CHANNEL play MODE to be discussed later in this document.) All four of the PlayMap bytes could even be the same wave number. This would cause that wave to be output of all 4 Amiga channels simultaneously. NumOfWaves is simply the number of waves in the sound file. Format is the number of significant bits in every sample of a wave. For example, if Format = 8, then this means that the sample data is an 8 bit format, and that every sample of the wave can be expressed by a single BYTE. (A 16 bit sample would need a WORD for every sample point). Each bit of the Flags byte, when set, means the following: Bit #0 - File continued on another disc. This might occur if the SAMP file was too large to fit on 1 floppy. The accepted practice (as incor- porated by Yamaha's TX sampler and Casio's FZ-1 for example) is to dump as much as possible onto one disc and set a flag to indicate that more is on another disc's file. The name of the files must be the related. The continuation file should have its own SAMP header MHDR, and BODY chunks. This file could even have its continuation bit set, etc. Never chop a sample wave in half. Always close the file on 1 disc after the last wave which can be completely saved. Resume with the next wave within the BODY of the continuation file. Also, the NumOfWaves in each file's BODY should be the number saved on that disc (not the total number in all combined disk files). See the end of this document for filename conventions. In C, here is how the PlayMap is used when receiving a midi note-on event: MapOffset = (UBYTE) MidiNoteNumber * numOfChans; /* MidiNoteNumber is the received note number (i.e. the second byte of a midi note-on event. numOfChans is from the SAMP MHDR. */ chan0waveNum = (UBYTE) playMap[MapOffset]; chan1waveNum = (UBYTE) playMap[MapOffset+1]; chan2waveNum = (UBYTE) playMap[MapOffset+2]; chan3waveNum = (UBYTE) playMap[MapOffset+3]; if (chan0waveNum != 0) { /* get the pointer to wave #1's data, determine the values that need to be passed to the audio device, and play this wave on Amiga audio channel #0 (if INDEPENDANT PlayMode) */ } /* do the same with the other 3 channel's wave numbers */ In assembly, the "MHDR" structure looks like this: CNOP 0,2 MHDR dc.b 'MHDR' sizeOfMHDR dc.l [this is 6 + (NumOfChans * 128) ] NumOfWaves dc.b [a byte count of the # of waves in the file] Format dc.b [a byte count of the # of significant bits in a sample point] Flags dc.b [bit mask] PlayMode dc.b [play MODE discussed later] NumOfChans dc.b [# of bytes per midi note for PlayMap] PlayMap ds.b [128 x NumOfChans bytes of initialized values] and a received MidiNoteNumber is interpreted as follows: moveq #0,d0 move.b MidiNoteNumber,d0 ;this is the received midi note # bmi.s Illegal_Number ;exit, as this is an illegal midi note # moveq #0,d1 move.b NumOfChans,d1 mulu.w d1,d0 ;MidiNoteNumber x NumOfChans lea PlayMap,a0 adda.l d0,a0 move.b (a0)+,chan0waveNum move.b (a0)+,chan1waveNum move.b (a0)+,chan2waveNum move.b (a0),chan3waveNum tst.b chan0waveNum beq.s Chan1 ;Now get the address of this wave number's sample data, determine the ;values that need to be passed to the audio device, and output the wave's ;data on Amiga chan 0 (assuming INDEPENDANT PlayMode). Chan1 tst.b chan1waveNum beq.s Chan2 ;do the same for the other wave numbers, etc. =====================THE "NAME" CHUNK========================= #define ID_NAME MakeID('N','A','M','E') If a NAME chunk is included in the file, then EVERY wave must have a name. Each name is NULL-terminated. The first name is for the first wave, and it is immediately followed by the second wave's name, etc. It is legal for a wave's name to be simply a NULL byte. For example, if a file contained 4 waves and a name chunk, the chunk might look like this: CNOP 0,2 Name dc.b 'NAME' sizeOfName dc.l 30 dc.b 'Snare Drum',0 ;wave 1 dc.b 'Piano 1',0 ;wave 2 dc.b 'Piano A4',0 ;wave 3 dc.b 0 ;wave 4 dc.b 0 NAME chunks should ALWAYS be padded out to an even number of bytes. (Hence the extra NULL byte in this example). The chunk's size should ALWAYS be even consequently. DO NOT USE the typical IFF method of padding a chunk out to an even number of bytes, but allowing an odd number size in the header. ==============THE "BODY" CHUNK=============== The "BODY" chunk is CONSIDERABLY different than the "8SVX" form. Like all chunks it has an ID. #define ID_BODY MakeID('B','O','D','Y') Every wave has an 80 byte waveHeader, followed by its data. The waveHeader structure is as follows: typedef struct { ULONG WaveSize; /* total # of BYTES in the wave (MUST be even) */ UWORD MidiSampNum; /* ONLY USED for Midi Dumps */ UBYTE LoopType, /* ONLY USED for Midi Dumps */ InsType; /* Used for searching for a certain instrument */ ULONG Period, /* in nanoseconds at original pitch */ Rate, /* # of samples per second at original pitch */ LoopStart, /* an offset in BYTES (from the beginning of the of the wave) where the looping portion of the wave begins. Set to WaveSize if no loop. */ LoopEnd; /* an offset in BYTES (from the beginning of the of the wave) where the looping portion of the wave ends. Set to WaveSize if no loop. */ UBYTE RootNote, /* the Midi Note # that plays back original pitch */ VelStart; /* 0 = NO velocity effect, 128 = negative direction, 64 = positive direction (it must be one of these 3) */ UWORD VelTable[16]; /* contains 16 successive offset values in BYTES from the beginning of the wave */ /* The ATAK and RLSE segments contain an EGPoint[] piece-wise linear envelope just like 8SVX. The structure of an EGPoint[] is the same as 8SVX. See that document for details. */ ULONG ATAKsize, /* # of BYTES in subsequent ATAK envelope. If 0, then no ATAK data for this wave. */ RLSEsize, /* # of BYTES in subsequent RLSE envelope If 0, then no RLSE envelope follows */ /* The FATK and FRLS segments contain an EGPoint[] piece-wise linear envelope for filtering purposes. This is included in the hope that future Amiga audio will incorporate a VCF (Voltage Controlled Filter). Until then, if you are doing any non-realtime digital filtering, you could store info here. */ sizeOfFATK, /* # of BYTES in FATK segment */ sizeOfFRLS, /* # of BYTES in FRLS segment */ USERsize; /* # of BYTES in the following data segment (not including USERtype). If zero, then no user data */ UWORD USERtype; /* See explanation below. If USERsize = 0, then ignore this. */ /* End of the waveHeader. */ /* The data for any ATAK, RLSE, FATK, FRLS, USER, and the actual wave data for wave #1 follows in this order: Now list each EGPoint[] (if any) for the VCA's (Voltage Controlled Amp) attack portion. Now list each EGPoint[] for the VCA's (Voltage Controlled Amp) release portion. List EGPoints[] (if any) for FATK. List EGPoints[] if any for FRLS */ Now include the user data here if there is any. Just pad it out to an even number of bytes and have USERsize reflect that. Finally, here is the actual sample data for the wave. The size (in BYTES) of this data is WaveSize. It MUST be padded out to an even number of bytes. */ } WaveFormInfo; /* END OF WAVE #1 */ /* The waveHeader and data for the next wave would now follow. It is the same form as the first wave */ In assembly, the BODY chunk looks like this: CNOP 0,2 BodyHEADER dc.b 'BODY' sizeOfBody dc.l [total bytes in the BODY chunk not counting 8 byte header] ; Now for the first wave WaveSize dc.l ;[total # of BYTES in this wave (MUST be even)] MidiSampNum dc.w ;[from Midi Sample Dump] ; ONLY USED for Midi Dumps LoopType dc.b ;[0 or 1] ; ONLY USED for Midi Dumps InsType dc.b 0 Period dc.l ;[period in nanoseconds at original pitch] Rate dc.l ;[# of samples per second at original pitch] LoopStart dc.l ;[an offset in BYTES (from the beginning of the ; of the wave) to where the looping ; portion of the wave begins.] LoopEnd dc.l ;[an offset in BYTES (from the beginning of the ; of the wave) to where the looping ; portion of the wave ends] RootNote dc.b ;[the Midi Note # that plays back original pitch] VelStart dc.b ;[0, 64, or 128] VelTable dc.w ;[first velocity offset] dc.w ;[second velocity offset]...etc ds.w 14 ;...for a TOTAL of 16 velocity offsets ATAKsize dc.l ;# of BYTES in subsequent ATAK envelope. ;If 0, then no ATAK data for this wave. RLSEsize dc.l ;# of BYTES in subsequent RLSE envelope ;If 0, then no RLSE data FATKsize dc.l ;# of BYTES in FATK segment FRLSsize dc.l ;# of BYTES in FRLS segment USERsize dc.l ;# of BYTES in the following User data ;segment (not including USERtype). ;If zero, then no user data USERtype dc.w ; See explanation below. If USERsize ; = 0, then ignore this. ;Now include the EGpoints[] (data) for the ATAK if any ;Now the EGpoints for the RLSE ;Now the EGpoints for the FATK ;Now the EGpoints for the FLSR ;Now include the user data here if there is any. Just pad ;it out to an even number of bytes. ;After the userdata (if any) is the actual sample data for ;the wave. The size (in BYTES) of this segment is WaveSize. ;It MUST be padded out to an even number of bytes. ; END OF WAVE #1 =============STRUCTURE OF AN INDIVIDUAL SAMPLE POINT============= Even though the next generation of computers will probably have 16 bit audio, and 8 bit sampling will quickly disappear, this spec has sizes expressed in BYTES. (ie LoopStart, WaveSize, etc.) This is because each successive address in RAM is a byte to the 68000, and so calculating address offsets will be much easier with all sizes in BYTES. The Midi sample dump, on the other hand, has sizes expressed in WORDS. What this means is that if you have a 16 bit wave, for example, the WaveSize is the total number of BYTES, not WORDS, in the wave. Also, there is no facility for storing a compression type. This is because sample data should be stored in linear format (as per the MIDI spec). Currently, all music samplers, regardless of their internal method of playing sample data must transmit and expect to receive sample dumps in a linear format. It is up to each device to translate the linear format into its own compression scheme. For example, if you are using an 8 bit compression scheme that yields a 14 bit linear range, you should convert each sample data BYTE to a decom- pressed linear WORD when you save a sound file. Set the MHDR's Format to 14. It is up to the application to do its own compression upon loading a file. The midi spec was set up this way because musical samplers need to pass sample data between each other, and computers (via a midi interface). Since there are almost as many data compression schemes on the market as there are musical products, it was decided that all samplers should expect data received over midi to be in LINEAR format. It seems logical to store it this way on disc as well. Therefore, any software program "need not know" how to decompress another software program's SAMP file. When 16 bit sampling is eventually implemented there won't be much need for compression on playback anyway. The continuation Flag solves the problem of disc storage as well. Since the 68000 can only perform math on BYTES, WORDS, or LONGS, it has been decided that a sample point should be converted to one of these sizes when saved in SAMP as follows: ORIGINAL significant bits SAMP sample point size 8 BYTE 9 to 16 WORD 17 to 28 LONG Furthermore, the significant bits should be left-justified since it is easier to perform math on the samples. So, for example, an 8 bit sample point (like 8SVX) would be saved as a BYTE with all 8 bits being significant. The MHDR's Format = 8. No conversion is necessary. A 12 bit sample point should be stored as a WORD with the significant bits being numbers 4 to 15. (i.e shift the 12-bit WORD 4 places to the left). Bits 0, 1, 2 and 3 may be zero (unless some 16-bit math was performed and you wish to save these results). The MHDR's Format = 12. In this way, the sample may be loaded and manipulated as a 16-bit wave, but when transmitted via midi, it can be converted back to 12 bits (rounded and shifted right by 4). A 16 bit sample point would be saved as a WORD with all 16 bits being significant. The MHDR's Format = 16. No conversion is necessary. ============== The waveHeader explained ============== The WaveSize is, as stated, the number of BYTES in the wave's sample table. If your sample data consisted of the following 8 bit samples: BYTE 100,-90,80,-60,30,35,40,-30,-35,-40,00,12,12,10 then WaveSize = 14. (PAD THE DATA OUT TO AN EVEN NUMBER OF BYTES!) The MidiSampNum is ONLY used to hold the sample number received from a MIDI Sample Dump. It has no bearing on where the wave should be placed in a SAMP file. Also, the wave numbers in the PlayMap are between 1 to 255, with 1 being the number of the first wave in the file. Remember that a wave number of 0 is reserved to mean "no wave to play back". Likewise, the LoopType is only used to hold info from a MIDI sample dump. The InsType is explained at the end of this document. Often it will be set to 0. The RootNote is the Midi Note number that will play the wave back at it's original, recorded pitch. For example, consider the following excerpt of a PlayMap: PlayMap {2,0,0,4 /* Midi Note #0 channel assignment */ 4,100,1,0 /* Midi Note #1 " " */ 1,4,0,0 /* Midi Note #2 " " */ 60,2,1,1...} /* Midi Note #3 " " */ Notice that Midi Notes 0, 1, and 2 are all set to play wave number 4 (on Amiga channels 3, 0, and 1 respectively). If we set wave 4's RootNote = 1, then receiving Midi Note number 1 would play back wave 4 (on Amiga channel 0) at it's original pitch. If we receive a Midi Note number 0, then wave 4 would be played back on channel 3) a half step lower than it's original pitch. If we receive Midi Note number 2, then wave 4 would be played (on channel 1) a half step higher than it's original pitch. If we receive Midi Note number 3, then wave 4 would not be played at all because it isn't specified in the PlayMap bytes for Midi Note number 3. The Rate is the number of samples per second of the original pitch. For example, if Rate = 20000, then to play the wave at it's original pitch, the sampling period would be: (1/20000)/.279365 = .000178977 #define AUDIO_HARDWARE_FUDGE .279365 where .279365 is the Amiga Fudge Factor (a hardware limitation). Since the amiga needs to see the period in terms of microseconds, move the decimal place to the right 6 places and our sampling period = 179 (rounded to an integer). In order to play the wave at higher or lower pitches, one would need to "transpose" this period value. By specifying a higher period value, the Amiga will play back the samples slower, and a lower pitch will be achieved. By specifying a lower period value, the amiga will play back the sample faster, and a higher pitch will be achieved. By specifying this exact period, the wave will be played back exactly "as it was recorded (sampled)". ("This period is JUST RIGHT!", exclaimed GoldiLocks.) Later, a method of transposing pitch will be shown using a "look up" table of periods. This should prove to be the fastest way to transpose pitch, though there is nothing in the SAMP format that compels you to do it this way. The LoopStart is a BYTE offset from the beginning of the wave to where the looping portion of the wave begins. For example, if SampleData points to the start of the wave, then SampleData + LoopStart is the start address of the looping portion. In 8SVX, the looping portion was referred to as repeatHiSamples. The data from the start of the wave up to the start of the looping portion is the oneShot portion of the wave. LoopEnd is a BYTE offset from the beginning of the wave to where the looping portion ends. This might be the very end of the wave in memory, or perhaps there might be still more data after this point. You can choose to ignore this "trailing" data and play back the two other portions of the wave just like an 8SVX file (except that there are no other interpolated octaves of this wave). VelTable contains 16 BYTE offsets from the beginning of the wave. Each successive value should be greater (or equal to) the preceding value. If VelStart = POSITIVE (64), then for each 8 increments in Midi Velocity above 0, you move UP in the table, add this offset to the wave's beginning address (start of oneShot), and start playback at that address. Here is a table relating received midi note-on velocity vs. start playback address for POSITIVE VelStart. SamplePtr points to the beginning of the sample. If midi velocity = 0, then don't play a sample, this is a note off If midi velocity = 1 to 7, then start play at SamplePtr + VelTable[0] If midi velocity = 8 to 15, then start at SamplePtr + VelTable[1] If midi velocity = 16 to 23, then start at SamplePtr + VelTable[2] If midi velocity = 24 to 31, then start at SamplePtr + VelTable[3] If midi velocity = 32 to 39, then start at SamplePtr + VelTable[4] If midi velocity = 40 to 47, then start at SamplePtr + VelTable[5] If midi velocity = 48 to 55, then start at SamplePtr + VelTable[6] If midi velocity = 56 to 63, then start at SamplePtr + VelTable[7] If midi velocity = 64 to 71, then start at SamplePtr + VelTable[8] If midi velocity = 72 to 79, then start at SamplePtr + VelTable[9] If midi velocity = 80 to 87, then start at SamplePtr + VelTable[10] If midi velocity = 88 to 95, then start at SamplePtr + VelTable[11] If midi velocity = 96 to 103, then start at SamplePtr + VelTable[12] If midi velocity = 104 to 111, then start at SamplePtr + VelTable[13] If midi velocity = 112 to 119, then start at SamplePtr + VelTable[14] If midi velocity = 120 to 127, then start at SamplePtr + VelTable[15] We don't want to specify a scale factor and use integer division to find the sample start. This would not only be slow, but also, it could never be certain that the resulting sample would be a zero crossing if the start point is calcu- lated "on the fly". The reason for having a table is so that the offsets can be be initially set on zero crossings via an editor. This way, no audio "clicks" guaranteed. This table should provide enough resolution. If VelStart = NEGATIVE (128), then for each 8 increments in midi velocity, you start from the END of VelTable, and work backwards. Here is a table for NEGATIVE velocity start. If midi velocity = 0, then don't play a sample, this is a note off If midi velocity = 1 to 7, then start play at SamplePtr + VelTable[15] If midi velocity = 8 to 15, then start at SamplePtr + VelTable[14] If midi velocity = 16 to 23, then start at SamplePtr + VelTable[13] If midi velocity = 24 to 31, then start at SamplePtr + VelTable[12] If midi velocity = 32 to 39, then start at SamplePtr + VelTable[11] If midi velocity = 40 to 47, then start at SamplePtr + VelTable[10] If midi velocity = 48 to 55, then start at SamplePtr + VelTable[9] If midi velocity = 56 to 63, then start at SamplePtr + VelTable[8] If midi velocity = 64 to 71, then start at SamplePtr + VelTable[7] If midi velocity = 72 to 81, then start at SamplePtr + VelTable[6] If midi velocity = 80 to 87, then start at SamplePtr + VelTable[5] If midi velocity = 88 to 95, then start at SamplePtr + VelTable[4] If midi velocity = 96 to 103, then start at SamplePtr + VelTable[3] If midi velocity = 104 to 111, then start at SamplePtr + VelTable[2] If midi velocity = 112 to 119, then start at SamplePtr + VelTable[1] If midi velocity = 120 to 127, then start at SamplePtr + VelTable[0] In essence, increasing midi velocity starts playback "farther into" the wave for POSITIVE VelStart. Increasing midi velocity "brings the start point back" toward the beginning of the wave for NEGATIVE VelStart. If VelStart is set to NONE (0), then the wave's playback start should not be affected by the table of offsets. What is the use of this feature? As an example, when a snare drum is hit with a soft volume, its initial attack is less pronounced than when it is struck hard. You might record a snare being hit hard. By setting VelStart to a NEGATIVE value and setting up the offsets in the Table, a lower midi velocity will "skip" the beginning samples and thereby tend to soften the initial attack. In this way, one wave yields a true representation of its instrument throughout its volume range. Furthermore, stringed and plucked instruments (violins, guitars, pianos, etc) exhibit different attacks at different volumes. VelStart makes these kinds of waves more realistic via a software implementation. Also, an application program can allow the user to enable/ disable this feature. See the section "Making the Velocity Table" for info on how to best choose the 16 table values. =========MIDI VELOCITY vs. AMIGA CHANNEL VOLUME============ The legal range for Midi Velocity bytes is 0 to 127. (A midi velocity of 0 should ALWAYS be interpreted as a note off). The legal range for Amiga channel volume is 0 to 64. Since this is half of the midi range, a received midi velocity should be divided by 2 and add 1 (but only AFTER checking for a received midi velocity of 0). An example of how to implement a received midi velocity in C: If ( ReceivedVelocity != 0 && ReceivedVelocity < 128 ) { /* the velocity byte of a midi message */ If (velStart != 0) { tableEntry = ReceivedVelocity / 8; If (velStart == 64) { /* Is it POSITIVE */ startOfWave = SamplePtr + velTable[tableEntry]; /* ^where to find the sample start point */ } If (velStart == 128) { /* Is it NEGATIVE */ startOfWave = SamplePtr + velTable[15 - tableEntry]; } volume = (receivedVelocity/2 + 1; /* playback volume */ /* Now playback the wave */ } } In assembly, lea SampleData,a0 ;the start addr of the sample data moveq #0,d0 move.b ReceivedVelocity,d0 ;the velocity byte of a midi message beq A_NoteOff ;If zero, branch to a routine to ;process a note-off message. bmi Illegal_Vol ;exit if received velocity > 127 ;---Check for velocity start feature ON, and direction move.b VelStart,d1 beq.s Volume ;skip the velocity offset routine if 0 bmi.s NegativeVel ;is it NEGATIVE? (128) ;---Positive velocity offset move.l d0,d1 ;duplicate velocity lsr.b #3,d1 ;divide by 8 add.b d1,d1 ;x 2 because we need to fetch a word lea VelTable,a1 ;start at table's HEAD adda.l d1,a1 ;go forward move.w (a1),d1 ;get the velocity offet adda.l d1,a0 ;where to start actual playback bra.s Volume NegativeVel: ;---Negative velocity offset move.l d0,d1 ;duplicate velocity lsr.b #3,d1 ;divide by 8 add.b d1,d1 ;x 2 because we need to fetch a word lea VelTable+30,a1 ;start at table's END suba.l d1,a1 ;go backwards move.w (a1),d1 ;get the velocity offset adda.l d1,a0 ;where to start actual playback ;---Convert Midi velocity to an Amiga volume Volume lsr.b #1,d0 ;divide by 2 addq.b #1,d0 ;an equivalent Amiga volume ;---Now a0 and d0 are the address of sample start, and volume ================= AN EGpoint (envelope generator) ================ A single EGpoint is a 6 byte structure as follows: EGpoint1: dc.w ;[the duration in milliseconds] dc.l ;[the volume factor - fixed point, 16 bits to the left of the ;decimal point and 16 to the right.] The volume factor is a fixed point where 1.0 ($00010000) represents the MAXIMUM volume possible. (i.e. No volume factor should exceed this value.) The last EGpoint in the ATAK is always the sustain point. Each EG's volume is determined from 0.0, not as a difference from the previous EG's volume. I hope that this clears up the ambiguity in the original 8SVX document. So, to recreate an amplifier envelope like this: /\ / \____ / \ / \ | | | | | 1 2 3 4 Stages 1, 2, and 3 would be in the ATAK data, like so: ;Stage 1 dc.w 100 ;take 100ms dc.l $00004000 ;go to this volume dc.w 100 dc.l $00008000 dc.w 100 dc.l $0000C000 dc.w 100 dc.l $00010000 ;the "peak" of our attack is full volume ;Stage 2 dc.w 100 dc.l $0000C000 ;back off to this level dc.l 100 dc.l $00008000 ;this is where we hold (SUSTAIN) until the note is turned ;off. (We are now holding at stage 3) Now the RLSE data would specify stage 4 as follows: dc.w 100 dc.l $00004000 dc.w 100 dc.l $00000000 ;the volume is 0 ===============ADDITIONAL USER DATA SECTION================= There is a provision for storing user data for each wave. This is where an application can store Amiga hardware info, or other, application specific info. The waveHeader's USERtype tells what kind of data is stored. The current types are: #define SPECIFIC 0 #define VOLMOD 1 #define PERMOD 2 #define LOOPING 3 SPECIFIC (0) - application specific data. It should be stored in a format that some application can immediately recognize. (i.e. a "format within" the SAMP format) If the USERtype is SPECIFIC, and an application doesn't find some sort of header that it can re- cognize, it should conclude that this data was put there by "someone else", and ignore the data. VOLMOD (1) - This data is for volume modulation of an Amiga channel as described by the ADKCON register. This data will be sent to the modulator channel of the channel set to play the wave. PERMOD (2) - This data is for period modulation of an Amiga channel as described by the ADKCON register. This data will be sent to the modulator channel of the channel set to play the wave. LOOPING (3) - This contains more looping points for the sample. There are some samplers that allow more than just one loop (Casio products primarily). Additional looping info can be stored in this format: UWORD numOfLoops; /* number of loop points to follow */ ULONG StartLoop1, /* BYTE offset from the beginning of the sample to the start of loop1 */ EndLoop1, /* BYTE offset from the beginning of the sample to the end of loop1 */ StartLoop2, /* ...etc */ =========Converting Midi Sample Dump to SAMP========= SEMANTICS: When MIDI literature talks about a sample, usually it means a collection of many sample points that make up what we call "a wave". Therefore, a Midi Sample Dump sends all the sample data that makes up ONE wave. A SAMP file is designed to hold up to 255 of these waves (midi dumps). The Midi Sample Dump specifies playback rate only in terms of a sample PERIOD in nanoseconds. SAMP also expresses playback in terms of samples per second (frequency). The Amiga needs to see its period rounded to the nearest microsecond. If you take the sample period field of a Midi sample Dump (the 8th, 9th, and 10th bytes of the Dump Header LSB first) which we will call MidiSamplePer, and the Rate of a SAMP file, here is the relationship: Rate = (1/MidiSamplePer) x 10E9 Also the number of samples (wave's length) in a Midi Sample Dump (the 11th, 12th, and 13th bytes of the Dump header) is expressed in WORDS. SAMP's WaveSize is expressed in the number of BYTES. (For the incredibly stupid), the relationship is: WaveSize = MidiSampleLength x 2 A Midi sample dump's LoopStart point and LoopEnd point are also in WORDS as versus the SAMP equivalents expressed in BYTES. A Midi sample dump's sample number can be 0 to 65535. A SAMP file can hold up to 255 waves, and their numbers in the playmap must be 1 to 255. (A single, Midi Sample Dump only sends info on one wave.) When recieving a Midi Sample Dump, just store the sample number (5th and 6th bytes of the Dump Header LSB first) in SAMP's MidiSampNum field. Then forget about this number until you need to send the wave back to the Midi instrument from whence it came. A Midi Dump's loop type can be forward, or forward/backward. Amiga hardware supports forward only. You should store the Midi Dump's LoopType byte here, but ignore it otherwise until/unless Amiga hardware supports "reading audio data" in various ways. If so, then the looptype is as follows: forward = 0, backward/forward = 1 A Midi Dump's sample format byte is the same as SAMP's. ===================== INTERPRETING THE PLAYMODE ========================== PlayMode specifies how the bytes in the PlayMap are to be interpreted. Remember that a PlayMap byte of 0 means "No Wave to Play". #define INDEPENDANT 0 #define MULTI 1 #define STEREO 2 #define PAN 3 PlayMode types: INDEPENDANT (0) - The wave #s for a midi note are to be output on Amiga audio channels 0, 1, 2, and 3 respectively. If the NumOfChans is < 4, then only use that many channels. MULTI (1) - The first wave # (first of the PlayMap bytes) for a midi note is to be output on any free channel. The other wave numbers are ignored. If all four channels are in play, the application can decide whether to "steal" a channel. STEREO (2) - The first wave # (first of the PlayMap bytes) is to be output of the Left stereo jack (channel 1 or 3) and if there is a second wave number (the second of the PlayMap bytes), it is to be output the Right jack (channel 2 or 4). The other wave numbers are ignored. PAN (3) - This is just like STEREO except that the volume of wave 1 should start at its initial volume (midi velocity) and fade to 0. At the same rate, wave 2 should start at 0 volume and rise to wave #1's initial level. The net effect is that the waves "cross" from Left to Right in the stereo field. This is most effective when the wave numbers are the same. (ie the same wave) The application program should set the rate. Also, the application can reverse the stereo direction (ie Right to Left fade). The most important wave # to be played back by a midi note should be the first of the PlayMap bytes. If the NumOfChans > 1, the second PlayMap byte should be a defined wave number as well (even if it is deliberately set to the same value as the first byte). This insures that all 4 PlayModes will have some effect on a given SAMP file. Also, an application should allow the user to change the PlayMode at will. The PlayMode stored in the SAMP file is only a default or initial set-up condition. =================== MAKING A TRANSPOSE TABLE ===================== In order to allow a wave to playback over a range of musical notes, (+/- semitones), its playback rate must be raised or lowered by a set amount. From one semitone to the next, this set amount is by a factor of the 12th root of 2 (assuming a western, equal-tempered scale). Here is a table that shows what factor would need to be multiplied by the sampling rate in order to transpose the wave's pitch. Pitch in relation to the Root Multiply Rate by this amount ------------------------------- ------------------------------ DOWN 6 semitones 0.5 DOWN 5 1/2 semitones 0.529731547 DOWN 5 semitones 0.561231024 DOWN 4 1/2 semitones 0.594603557 DOWN 4 semitones 0.629960525 DOWN 3 1/2 semitones 0.667419927 DOWN 3 semitones 0.707106781 DOWN 2 1/2 semitones 0.749153538 DOWN 2 semitones 0.793700526 DOWN 1 1/2 semitones 0.840896415 DOWN 1 semitones 0.890898718 DOWN 1/2 semitone 0.943874312 ORIGINAL_PITCH 1.0 /* rootnote's pitch */ UP 1/2 semitone 1.059463094 UP 1 semitones 1.122562048 UP 1 1/2 semitones 1.189207115 UP 2 semitones 1.259921050 UP 2 1/2 semitones 1.334839854 UP 3 semitones 1.414213562 UP 3 1/2 semitones 1.498307077 UP 4 semitones 1.587401052 UP 4 1/2 semitones 1.681792830 UP 5 semitones 1.781797436 UP 5 1/2 semitones 1.887748625 UP 6 semitones 2 For example, if the wave's Rate is 18000 hz, and you wish to play the wave UP 1 semitone, then the playback rate is: 18000 x 1.122562048 = 20206.11686 hz The sampling period for the Amiga is therefore: (1/20206.11686)/.279365 = .000177151 and to send it to the Audio Device, it is rounded and expressed in micro- seconds: 177 Obviously, this involves floating point math which can be time consuming and impractical for outputing sound in real-time. A better method is to con- struct a transpose table that contains the actual periods already calculated for every semitone. The drawback of this method is that you need a table for EVERY DIFFERENT Rate in the SAMP file. If all the Rates in the file happened to be the same, then only one table would be needed. Let's assume that this is the case, and that the Rate = 18000 hz. Here is a table containing enough entries to transpose the waves +/- 6 semitones. Pitch in relation to the Root The Amiga Period (assuming rate = 18000 hz) ------------------------------- ------------------------------ Transposition_table[TRANS_TABLE_SIZE]={ /* DOWN 6 semitones */ 398, /* DOWN 5 1/2 semitones */ 375, /* DOWN 5 semitones */ 354, /* DOWN 4 1/2 semitones */ 334, /* DOWN 4 semitones */ 316, /* DOWN 3 1/2 semitones */ 298, /* DOWN 3 semitones */ 281, /* DOWN 2 1/2 semitones */ 265, /* DOWN 2 semitones */ 251, /* DOWN 1 1/2 semitones */ 236, /* DOWN 1 semitones */ 223, /* DOWN 1/2 semitone */ 211, /* ORIGINAL_PITCH */ 199, /* rootnote's pitch */ /* UP 1/2 semitone */ 187, /* UP 1 semitones */ 177, /* UP 1 1/2 semitones */ 167, /* UP 2 semitones */ 157, /* UP 2 1/2 semitones */ 148, /* UP 3 semitones */ 141, /* UP 3 1/2 semitones */ 133, /* Since the minimum Amiga period = 127 the following are actually out of range. */ /* UP 4 semitones */ 125, /* UP 4 1/2 semitones */ 118, /* UP 5 semitones */ 112, /* UP 5 1/2 semitones */ 105, /* UP 6 semitones */ 99 }; Let's assume that (according to the PlayMap) midi note #40 is set to play wave number 3. Upon examining wave 3's structure, we discover that the Rate = 18000, and the RootNote = 38. Here is how the Amiga sampling period is calulated using the above 18000hz "transpose chart" in C: /* MidiNoteNumber is the received midi note's number (here 40) */ #define ORIGINAL_PITCH TRANS_TABLE_SIZE/2 + 1 /* TRANS_TABLE_SIZE is the number of entries in the transposition table (dynamic, ie this can change with the application) */ transposeAmount = (LONG) (MidiNoteNumber - rootNote); /* make it a SIGNED LONG */ amigaPeriod = Transposition_table[ORIGINAL_PITCH + transposeAmount]; In assembly, the 18000hz transpose chart and above example would be: Table dc.w 398 dc.w 375 dc.w 354 dc.w 334 dc.w 316 dc.w 298 dc.w 281 dc.w 265 dc.w 251 dc.w 236 dc.w 223 dc.w 211 ORIGINAL_PITCH dc.w 199 ; rootnote's pitch dc.w 187 dc.w 177 dc.w 167 dc.w 157 dc.w 148 dc.w 141 dc.w 133 ; Since the minimum Amiga period = 127, the following ; are actually out of range. dc.w 125 dc.w 118 dc.w 112 dc.w 105 dc.w 99 lea ORIGINAL_PITCH,a0 move.b MidiNoteNumber,d0 ;the received note number sub.b RootNote,d0 ;subtract the wave's root note ext.w d0 ext.l d0 ;make it a signed LONG add.l d0,d0 ;x 2 in order to fetch a WORD adda.l d0,a0 move.w (a0),d0 ;the Amiga Period (WORD) Note that these examples don't check to see if the transpose amount is beyond the number of entries in the transpose table. Nor do they check if the periods in the table are out of range of the Amiga hardware. ===================== MAKING THE VELOCITY TABLE ====================== The 16 entries in the velocity table should be within the oneShot portion of the sample (ie not in the looping portion). THe first offset, VelTable[0] should be set to zero (in order to play back from the beginning of the data). The subsequent values should be increasing numbers. If you are using a graphic editor, try choosing offsets that will keep you within the initial attack portion of the wave. In practice, these values will be relatively close together within the wave. Always set the offsets so that when they are added to the sample start point, the resulting address points to a sample value of zero (a zero crossing point). This will eliminate pops and clicks at the beginning of the playback. In addition, the start of the wave should be on a sample with a value of zero. The last sample of the oneShot portion and the first sample of the looping portion should be approximately equal, (or zero points). The same is true of the first and last samples of the looping portion. Finally, try to keep the slopes of the end of the oneShot, the beginning of the looping, and the end of the looping section, approximately equal. All this will eliminate noise on the audio output and provide "seamless" looping. ======================== THE INSTRUMENT TYPE ========================== Many SMUS players search for certain instruments by name. Not only is this slow (comparing strings), but if the exact name can't be found, then it is very difficult and time-consuming to search for a suitable replacement. For this reason, many SMUS players resort to "default" instruments even if these are nothing like the desired instruments. The InsType byte in each waveHeader is meant to be a numeric code which will tell an SMUS player exactly what the instrument is. In this way, the SMUS player can search for the correct "type" of instrument if it can't find the desired name. The type byte is divided into 2 nibbles (4 bits for you C programmers) with the low 4 bits representing the instrument "family" as follows: 1 = STRING, 2 = WOODWIND, 3 = KEYBOARD, 4 = GUITAR, 5 = VOICE, 6 = DRUM1, 7 = DRUM2, 8 = PERCUSSION1, 9 = BRASS1, A = BRASS2, B = CYMBAL, C = EFFECT1, D = EFFECT2, E = SYNTH, F is undefined at this time Now, the high nibble describes the particular type within that family. For the STRING family, the high nibble is as follows: 1 = VIOLIN BOW, 2 = VIOLIN PLUCK, 3 = VIOLIN GLISSANDO, 4 = VIOLIN TREMULO, 5 = VIOLA BOW, 6 = VIOLA PLUCK, 7 = VIOLA GLIS, 8 = VIOLA TREM, 9 = CELLO BOW, A = CELLO PLUCK, B = CELLO GLIS, C = CELLO TREM, D = BASS BOW, E = BASS PLUCK (jazz bass), F = BASS TREM For the BRASS1 family, the high nibble is as follows: 1 = BARITONE SAX, 2 = BARI GROWL, 3 = TENOR SAX, 4 = TENOR GROWL, 5 = ALTO SAX, 6 = ALTO GROWL, 7 = SOPRANO SAX, 8 = SOPRANO GROWL, 9 = TRUMPET, A = MUTED TRUMPET, B = TRUMPET DROP, C = TROMBONE, D = TROMBONE SLIDE, E = TROMBONE MUTE For the BRASS2 family, the high nibble is as follows: 1 = FRENCH HORN, 2 = TUBA, 3 = FLUGAL HORN, 4 = ENGLISH HORN For the WOODWIND family, the high nibble is as follows: 1 = CLARINET, 2 = FLUTE, 3 = PAN FLUTE, 4 = OBOE, 5 = PICCOLO, 6 = RECORDER, 7 = BASSOON, 8 = BASS CLARINET, 9 = HARMONICA For the KEYBOARD family, the high nibble is as follows: 1 = GRAND PIANO, 2 = ELEC. PIANO, 3 = HONKYTONK PIANO, 4 = TOY PIANO, 5 = HARPSICHORD, 6 = CLAVINET, 7 = PIPE ORGAN, 8 = HAMMOND B-3, 9 = FARFISA ORGAN, A = HARP For the DRUM1 family, the high nibble is as follows: 1 = KICK, 2 = SNARE, 3 = TOM, 4 = TIMBALES, 5 = CONGA HIT, 6 = CONGA SLAP, 7 = BRUSH SNARE, 8 = ELEC SNARE, 9 = ELEC KICK, A = ELEC TOM, B = RIMSHOT, C = CROSS STICK, D = BONGO, E = STEEL DRUM, F = DOUBLE TOM For the DRUM2 family, the high nibble is as follows: 1 = TIMPANI, 2 = TIMPANI ROLL, 3 = LOG DRUM For the PERCUSSION1 family, the high nibble is as follows: 1 = BLOCK, 2 = COWBELL, 3 = TRIANGLE, 4 = TAMBOURINE, 5 = WHISTLE, 6 = MARACAS, 7 = BELL, 8 = VIBES, 9 = MARIMBA, A = XYLOPHONE, B = TUBULAR BELLS, C = GLOCKENSPEIL For the CYMBAL family, the high nibble is as follows: 1 = CLOSED HIHAT, 2 = OPEN HIHAT, 3 = STEP HIHAT, 4 = RIDE, 5 = BELL CYMBAL, 6 = CRASH, 7 = CHOKE CRASH, 8 = GONG, 9 = BELL TREE, A = CYMBAL ROLL For the GUITAR family, the high nibble is as follows: 1 = ELECTRIC, 2 = MUTED ELECTRIC, 3 = DISTORTED, 4 = ACOUSTIC, 5 = 12-STRING, 6 = NYLON STRING, 7 = POWER CHORD, 8 = HARMONICS, 9 = CHORD STRUM, A = BANJO, B = ELEC. BASS, C = SLAPPED BASS, D = POPPED BASS, E = SITAR, F = MANDOLIN (Note that an acoustic picked bass is found in the STRINGS - Bass Pluck) For the VOICE family, the high nibble is as follows: 1 = MALE AHH, 2 = FEMALE AHH, 3 = MALE OOO, 4 = FEMALE OOO, 5 = FEMALE BREATHY, 6 = LAUGH, 7 = WHISTLE For the EFFECTS1 family, the high nibble is as follows: 1 = EXPLOSION, 2 = GUNSHOT, 3 = CREAKING DOOR OPEN, 4 = DOOR SLAM, 5 = DOOR CLOSE, 6 = SPACEGUN, 7 = JET ENGINE, 8 = PROPELLER, 9 = HELOCOPTER, A = BROKEN GLASS, B = THUNDER, C = RAIN, D = BIRDS, E = JUNGLE NOISES, F = FOOTSTEP For the EFFECTS2 family, the high nibble is as follows: 1 = MACHINE GUN, 2 = TELEPHONE, 3 = DOG BARK, 4 = DOG GROWL, 5 = BOAT WHISTLE, 6 = OCEAN, 7 = WIND, 8 = CROWD BOOS, 9 = APPLAUSE, A = ROARING CROWDS, B = SCREAM, C = SWORD CLASH, D = AVALANCE, E = BOUNCING BALL, F = BALL AGAINST BAT OR CLUB For the SYNTH family, the high nibble is as follows: 1 = STRINGS, 2 = SQUARE, 3 = SAWTOOTH, 4 = TRIANGLE, 5 = SINE, 6 = NOISE So, for example if a wave's type byte was 0x26, this would be a SNARE DRUM. If a wave's type byte is 0, then this means "UNKNOWN" instrument. ===================== THE ORDER OF THE CHUNKS ========================= The SAMP header obviously must be first in the file, followed by the MHDR chunk. After this, the ANNO, (c), AUTH and NAME chunks may follow in any order, though none of these need appear in the file at all. The BODY chunk must be last. ================= FILENAME CONVENTIONS ================= For when it becomes necessary to split a SAMP file between floppies using the Continuation feature, the filenames should be related. The method is the following: The "root" file has the name that the user chose to save under. Subsequent files have an ascii number appended to the name to indicate what sublevel the file is in. In this way, a program can reload the files in the proper order. For example, if a user saved a file called "Gurgle", the first continuation file should be named "Gurgle1", etc. ============ WHY DOES ANYONE NEED SUCH A COMPLICATED FILE? ============== (or "What's wrong with 8SVX anyway?") In a nutshell, 8SVX is not adequate for professional music sampling. First of all, it is nearly impossible to use multi-sampling (utilizing several, different samples of any instrument throughout its musical range). This very reason alone makes it impossible to realistically reproduce a musical in- strument, as none in existance (aside from an electronic organ) uses inter- polations of a single wave to create its musical note range. Also, stretching a sample out over an entire octave range does grotesque (and VERY unmusical) things to such elements as the overtone structure, wind/percussive noises, the instrument's amplitude envelope, etc. The 8SVX format is designed to stretch the playback in exactly this manner. 8SVX ignores MIDI which is the de facto standard of musical data transmission. 8SVX does not allow storing data for features that are commonplace to pro- fessional music samplers. Such features are: velocity sample start, separate filter and envelopes for each sample, separate sampling rates, and various playback modes like stereo sampling and panning. SAMP attempts to remedy all of these problems with a format that can be used by a program that simulates these professional features in software. The format was inspired by the capabilities of the following musical products: EMU's EMAX, EMULATOR SEQUENTIAL CIRCUIT's PROPHET 2000, STUDIO 440 ENSONIQ's MIRAGE CASIO's FZ-1 OBERHEIM's DPX YAMAHA TX series So why does the Amiga need the SAMP format? Because professional musician's are buying computers. With the firm establishment of MIDI, musician's are buying and using a variety of sequencers, patch editors, and scoring programs. It is now common knowledge amoung professional musicians that the Amiga lags far behind IBM clones, Macintosh, and Atari ST computers in both music software and hardware support. Both Commodore and the current crop of short- sighted 3rd party Amiga developers are pigeon-holing the Amiga as "a video computer". It is important for music software to exploit whatever capabili- ties the Amiga offers before the paint and animation programs, genlocks, frame-grabbers, and video breadboxes are the only applications selling for the Amiga. Hopefully, this format, with the SAMP disk I/O library will make it possible for Amiga software to attain the level of professionalism that the other machines now boast, and the Amiga lacks.