Data AcQuisition And Real-Time Analysis
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The following is from the Daqarta Help system:



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Play Rate Absolute / Relative

Controls: Gen Dlg >> Stream >> Wave >> Play >> Rate
Macro: PlayRate

If the Play file was recorded at a sample rate different from that currently in use, this control allows you to select whether the Rate control should show Absolute rate, where 1.0000 means that the effective playback is the same as recorded, or Relative, where 1.0000 means that each output sample uses the next Play sample exactly.

For example, suppose the file was recorded at a sample rate of 20000 Hz but the current sample rate is 44100 Hz. If you set this control to Rel and set the main Rate to 1.0000, the file will play back faster by a ratio of 44100 / 20000 or 2.205 times faster. You would have to set Rate to 20000 / 44100 or 0.4535 in order to get the same effective playback rate as recorded.

Alternatively, if you set this control to Abs, then the above conversion is applied automatically and you get the original playback when Rate is 1.0000.

But note that it's not truly the "original" playback, since Daqarta must interpolate between samples to compensate, so there will be some distortion due to the linear interpolation. On the other hand, playing exactly one file sample for each output sample eliminates waveform distortion, but all the frequencies will be higher by a factor of 2.205 and the duration will only be 0.4535 as long.

Note also that when you change sample rate, the effective playback speed is changed proportionally. (This is different from ordinary repetitive waveforms, which are automatically adjusted to maintain their same output frequencies.) If Rate Relative is set, then the displayed Rate will not change because it shows the number of Play samples per output sample. If Rate Absolute is set, then Play Rate will be proportional to sample rate.

Macro Notes:

This control is only enabled when a Play file has been loaded.

L.1.PlayRate=Abs or L.1.PlayRate=1 sets Absolute Play Rate, PlayRate=Rel or PlayRate=0 sets Relative, and PlayRate=x toggles between the two.

See also Wave Dialog, Play Wave.


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