Resampling a soundfile

You can use this utility to alter the sampling rate of the digital recording. Since all CD players "read" audio signals with a 44.1 kHz speed you have to convert all audio files to this standard rate prior to putting it on a CD. The other standard output rates are, among others, 48 kHz (the rate used in a DAT equipment) and 32 kHz (the radio frequency). The procedure for sample rate conversion implemented in DART XP Pro has two important features:

Blad! Nieznany argument przelacznika.It provides truly professional resampling quality and, at the same time, is extremely fast (we bet you will not find a faster one elsewhere)

Blad! Nieznany argument przelacznika.It is not constrained to standard sampling rates, i.e. it can be used to convert any input rate to any output rate

When the output/input resampling ratio r is greater than one (upsampling) the output audio file is r times longer than the input one. If r is smaller than one (downsampling) the output file is r times shorter than the input file. For obvious reasons downsampling is faster than upsampling (think of the number of input/output operations in each case).

When downsampling is performed the bandwidth of the signal is reduced accordingly, that is, some high-frequency signal components are removed. This means that downsampling an audio signal r times and then upsampling it r times will not restore the original recording (downsampling is not a reversible operation). Since bandwidth reduction may result in audible sound distortions you should use this tool with caution.

NOTICE

The bandwidth of many old recordings is limited to 10 kHz, which means they can be "safely" sampled at the rate of 22 kHz. In cases like this consider recording and restoring the audio signal at a lower rate of 22 kHz prior to upsampling it to a CD rate of 44 kHz. There are at least two advantages of doing this:

1. Declicking is usually more effective at low sampling rates - at high rates clicks are less sharp and hence more difficult to detect and isolate. The same, to some extent, concerns denoising - since noise dominates the high-frequency portion of the signal spectrum, fast sampling decreases the overall signal-to-noise (SNR) ratio, which makes the restoration task more difficult.

2. Since resampling is less time consuming than declicking or denoising (dehissing) the "restore at lower rate and upsample" scheme works considerably faster than the "restore at higher rate" scheme.

Time synchronization

Comparing the resampled audio signal with its original version is a bit tricky - since both files differ in length the 'ordinary' synchronization, which does not take into account the sampling rates of displayed files, will fail to locate fragments of the recordings with identical contents. To help you compare several variants of the recording with different sampling rates a special time synchronization feature was added to the Preferences dialog available from the Options menu. When the Time sync box is checked and synchronization is switched on the cursors in all displayed windows are automatically time-aligned. This means that if the Play local command is used the same portion of the audio material will be played back irrespective of the corresponding sampling rates. Similarly, when a block of samples is selected in an active window the appropriately scaled (contracted or extended) blocks will be marked in the remaining windows.

NOTICE

When time synchronization is on and the compared files have different sampling rates, the time-aligned cursors have different relative positions within each window (unless placed exactly in the center of an active window). To put them exactly one over another, i.e. along the same vertical line, press the TAB key.