Creating Rectified-Wave Arbs

There are no Wave selections for rectified waveforms, but you can use the Daqarta Generator to create them and save them for use as Arb files.

Consider a rectified sine wave. A half-wave rectified sine has the negative portions clipped to zero; a full-wave rectified sine has the negative portions inverted to positive.

(Actually, for many purposes you can half-wave rectify a sine, or any other wave, by setting Level to 100% and DC Offset to -100%. The large negative Offset will appear on the trace, but since sound cards are AC-coupled it will not appear on the output. The spectrum of the generated signal will be the same, except for a peak at DC due to the offset.)

Half-Wave Rectified Sine:

You can create a half-wave rectified sine with Burst, by setting Rise and Fall to zero, Cycle to the duration of one full cycle, and High to half that value. Set Trigger to Gen Sync for best results. (If the wave does not appear stationary, go to the main Tone Freq dialog and make sure Tone Sync is set.)

This produces a lovely half-wave rectified sine. The problem is, if you want to change the frequency of the wave, you have to change the Burst settings to match. If you only have a few fixed frequencies, this can be handled by Macros. But want if you want to apply FM, or Sweep the frequency?

The solution is to record exactly one cycle of the wave to a file, and then use that as an Arb.

Arb files need to be in sizes of 1024, 2048, 4096, or 8192 samples; you should use 8192 for best resolution. So set Burst Cycle to 8192 samples, and High to 4096, toggling the units button from sec to Smpls as needed.

Now you need to set the main Tone Freq so that one cycle exactly fills 8192 samples. At the typical Sample Rate of 48000 samples/sec, that would be 48000 / 8192 = 5.8594 Hz. You will only see an eighth of the wave on the 1024-sample trace, but that's OK... it's the file that is important.

Now go to the DDisk Controls dialog (thin button under the DDisk button in the main toolbar, above Record) and select Triggered Start. At the bottom set Units to Samples, then set Write Size Preset to 8192. Set Write PreStart to 0. Click on the DDisk button and create a Save As file name, such as HalfSine; you can use the default .DQA file type.

Click Record, and almost immediately you will be prompted to keep the new file. Do that.

Now go back and toggle Burst off. In the Wave dialog, select Arb and click on an unused Arb button. Select the file you have just created. You'll see a half-wave sine, and you can set any frequency you want, and apply FM or Sweep as desired.

Full-Wave Rectified Sine:

This is actually easier than half-wave, since no Burst is needed. The trick is to set the sine frequency so that 8192 samples is only half of a cycle. At 48000 Hz sample rate, that would be 48000 / (2 * 8192) = 2.9297 Hz. Then record it just like the above, maybe calling it FullSine.

Note, however, that the file contains only a half-cycle of the rectified wave. That means that to generate the rectified version of any given frequency, you will need to set Tone Freq to twice that frequency.

See also Creating Arb Files with the Generator, Creating Arb Files From Text, Wave Dialog, Arb Wave.