Now what about an HQ chirp/sweep?

[Michael Kazmierski]

Hello,
I know I've been asking for so much lately, but I have yet to find a Screen-reader-accessible plugin that generates a sweep or chirp while still having a duration edit box. So due to both accessibility and being auditorily picky, I think people might benefit from an "HQ Sweep" or "HQ Chirp" Nyquist plugin. Unfortunately, given that I am not too familiar with Nyquist, I can explain what the controls would be.

"Waveform:" the same choices as in the HQ tone plugin
"Frequency Hertz start", "Frequency Hertz end", "Amplitude start", "Amplitude end", whatever the control label would be with choices "Linear" and "Logarithmic", and finally "Duration", edit box (rather than a series of read-only stuff that Jaws can't handle as in the standard chirp plugin). Only now, this plugin will make it so that the waveforms that use higher harmonics are bandlimited, exactly how it is in the HQ tone plugin. I don't think this would take too much effort to make, though if I knew Nyquist, I'd use the "HQ Tone" plugin as a place to base the HQ sweep on. Is it possible that anyone could attempt to try this? I'd love to have such a plugin, but for two reasons, I am not the biggest fan of the standard chirp. 1) At least with a screen reader, you can't type a duration, which needs to be accessible (the HQ tone duration box does work with screen reader), and 2) This ridiculous distortion effect I can't handle, just like the warping on old bagpipe records which I have. Thanks, sorry for the inconvenience, and good luck.



Michael

PS. After this, I seriously can't think of any more plugins to suggest.

[steve]

I don't think this would take too much effort to make,

Actually it would be quite a lot of work. In order to produce a high quality waveform, "HQ tone" creates a wavetable from the maximum number of harmonics possible below the Nyquist frequency (the Nyquist frequency is half the sample rate). The number of harmonics thus depends on both the root frequency and the sample rate. For a given sample rate, the higher the root frequency (the "fundamental" frequency), the smaller the number of harmonics. Thus for a chirp, the number of harmonics for the lower frequency end is greater than at the high frequency end. This means that a pre-calculated wavetable cannot be used unless accompanied by sufficient oversampling to prevent aliasing at the high end of the chirp, which could be up to 500 times oversampling if the available frequency range is retained, which could make the effect up to 500 times slower. So quite a lot of work, and a very slow effect at the end.

I wasn't aware that Audacity's built-in Chirp effect isn't accessible. Have you tried asking about that on the audacity4blind mailing list?

[Robert J. H.]

The standard Chirp works perfectly with NVDA.

[6mbi6nt]

Pardon my ignorance, I have just used Audacity the first time today.
I was trying to make a sine sweep, so I used Generate --> Chirp.
The problem is that there is some kind of noise, is it normal?
Is this noise related to the need of a high quality sweep (i.e. getting rid of the noise?)

[steve]

The problem is that there is some kind of noise, is it normal?

What kind of noise?