PSP MixSaturator

Construction and operation of the PSP MixSaturator

 

 

The analog saturation simulation algorithm

The analog saturation simulation algorithm is used for the treatment of a processed signal as a whole. It enables the user to use one of the seven nonlinearity curves.

There are six curves available, representing the nonlinearity of analog valve processing (Valve1, Valve2, Valve3) and tape saturation (Tape1, Tape2, Tape3), as well as a digital clipping curve.

Each nonlinearity curve gives a different sound for the material processed, as they differ in the arrangement and content of harmonics, as well as the threshold above which distortion becomes audible. The 'drive' slider enables the user to place the input signal on the nonlinearity curve with precision.

Below are descriptions of particular nonlinearity curves with diagrams of their characteristics. The diagram on the left shows the level of the output signal (output) in relation to the level of the input signal (input); the one on the right shows the increase in the basic compound content (marked in turquoise) and the harmonics (3h - magenta, 5h - red, 7h - blue, 9h - yellow) in relation to the sinusoidal level of the input signal (green).

The first three characteristics of the nonlinearity curve represent the way in which valve devices operate at different levels of saturation.

"Valve 1" is a characteristic which introduces very delicate distortion and enables the user to raise the recording level minimally. Its operation leads to an increased clarity in the processed sound and the depth of the sound recording. Thanks to these properties, it is possible to give single tracks, such as vocals or single instruments, or the whole recording, the sound quality of a high-class valve preamp.

 

"Valve 2" enables the user to achieve a greater amplification than "Valve 1" with the introduction of audible distortion. For this reason it is primarily intended for use in the processing of tracks with marked transients and high peak levels, characteristic of percussion instruments, drums and loops.

 

"Valve 3" has been designed to produce the sound of overdriven valve circuits. The use of this kind of sound is dependent on the processed material.

 

The next three characteristics of the nonlinearity curve are similar to the phenomena produced during the registration and playback of sound signals when using magnetic analog tape. They can be successfully used both for the simulation of slightly saturated sound and the simulation of strongly overdriven tape. Because of the shape of the curves, all three characteristics can raise the recording level by a similar degree. If the overdrive of the algorithm exceeds the maximum level (0db on the indicators and +14db on the meter) the level of the signal will be held or reduced according to further increases in the input signal.

"Tape 1" introduces gentle, barely audible distortion to high input level values. A distinct increase in the distortion content is noticeable in the -6 to 0dB range. The effect of the distortion is concentrated mainly on the third harmonic, which is why "Tape 1" is very good for processing signals with lesser harmonic values, as well as whole mixes.

 

The action of "Tape 2" is more aggressive. Audible distortion is introduced over a greater dynamic range. The effect of the distortion is gently spread over all of the harmonics. A high input-signal level of 3h above 0dB is characteristic of "Tape 2" and this is why it is perfect for processing percussion and drum sound, by significantly brightening the transients.

 

"Tape 3" is characterised by the introduction of distortion only as third and fifth harmonics up to the input level of 0dB. The signal is cut off above this value, due to the increase of all odd harmonics.

 

"Digital" is a typical example of digital clipping, which appears, for example, during the overdrive of analog-digital converters (ADC) or a signal recorded on digital media. No distortion is introduced up to the 0dB level, but above this level the distortion increases rapidly and spreads across all of the odd harmonics. The "digital" curve, in distinction from those previously mentioned, does not retain the possibility of increasing the signal level.

 

The correct adjustment of the algorithm parameters (settings of the shape and drive sliders) to the processed material makes it possible to obtain a full, clear sound and to modify the signal peaks which are short or too high, similar to the way in which high-quality analog equipment works. It is also possible to obtain purposefully audible distortion thanks to a wide range of settings.

Inappropriate use of the analog saturation simulation algorithm may lead to an undesired and audible reduction of transients and the loss of definition, due to a considerable increase in the level of distortion.

 

The bass frequencies processing algorithm

The aim of this algorithm is to add warmth to the sound within the bass frequencies range through adding harmonics and increasing the bass in a recording. The way in which this algorithm affects the sound resembles the action of analog tape, which introduces additional distortion to both even and odd bass frequencies. A wide range of settings makes it possible to obtain a considerably greater range of 'colour'. Technically, this algorithm is a combination of processing with the use of a nonlinearity curve similar to "Valve 2" (which, however, works at higher drive levels) with a special circuit which turns the signal's energy into even harmonic distortion. Below are diagrams which describe the operation of this circuit.
In the diagram on the right, the signal levels are marked with colours in the following way: green - input signal; turquoise - basic compound signal; magenta - second harmonics; red - third harmonics; blue - fourth harmonics; yellow - fifth harmonics.
The measurement of the harmonics content has been made at the signal level of 0dBFS and the setting of the warmth knob at 100%.

 

The treble frequencies processing algorithm

The processing of treble frequencies in the PSP MixSaturator is based on soft-knee compression. The shape of the compression curve is similar to the shape of nonlinearity curve "Valve 1", however, a very high drive level is possible here, due to a high degree of attenuation, which may even exceed 12dB.

Temporary characteristics are automatically selected, based on the set cut-off frequency of the treble frequencies filter. Due to this approach to the processing of treble frequencies, it is possible to simulate the saturation of the tape within this range, without increasing the level of distortion and aliasing.

 

The PSP MixSaturator block diagram

Description of terms used in the block diagram for the PSP MixSaturator processor

   
input plug-in input: regulates the input signal
output plug-in output: regulates the output signal
bass saturation bass frequencies processing algorithm
freq cut-off frequency of the filter
warmth addition of warmth to bass frequencies
adjust content of bass frequencies
bass on turning on the processing of bass frequencies
treble compression treble frequencies processing algorithm
freq cut-off frequency of the filter
comp treble frequencies compression
adjust treble frequencies content
treble on turning on the processing of treble frequencies
main saturation analog saturation simulation algorithm
drive drive level of the saturation simulation algorithm
shape selection of the nonlinearity characteristics
pre metering measuring signal levels after regulation of the input level
drive metering measuring drive levels of the saturation simulation algorithm
post metering measuring of the output signal levels
Process button activates these sections processor elements within the frame are active if the "process" button is on

 


PSP is a trademark of Projekt-CDO. "VST" is a trademark of Steinberg Soft - und Hardware GmbH. All others trademarks are the property of their respective owners.