Re: [LAD] Mixing audio: Noiseless volume changes

On March 18, 2013 06:47:16 PM you wrote: On Mon, Mar 18, 2013 at 5:50 PM, Tim E. Real <termtech(a)rogers.com> wrote: Hi again. Looking for any advice, tips, tricks, anecdotes etc. I want to eliminate or reduce 'zipper' noise on volume changes. So I'm looking at two techniques: Zero-crossing / zero-value signal detection, and slew-rate limiting. Code is almost done, almost ready to start testing each technique. Each technique has some advantages and disadvantages. If I use a slew-rate limiter, I figure for a sudden volume factor change from 0.0 to 1.0, if I limit the slew rate to say 0.01 per sample then after 100 samples the ramp will be done. But even with a fine ramp, this still might introduce artifacts in the audio. You cannot avoid artifacts in the audio. The only question is what is the nature of the artifacts. If I use a zero-crossing/zero-value detector and apply volume changes Zero crossing stuff is a completely bogus idea that needs to be eliminated from the lexicon of audio software. You will not be accomplishing anything trying to use such a technique, other than introduce even more artifacts (and rather horrendous ones at that). Even zero-valued samples are not particularly useful - keep in mind that what defines transducer (read: speaker) behaviour is power, not instantaneous volume. Just use sensibly short ramped changes. For the record, Ardour uses 64 or a JACK period size, whichever is, hmm, larger or smaller, can't recall. --p Wow, surprising answer. Can you elaborate a wee bit on the bogus point? What worse artifacts? Popping noise will be heard if sudden volume change is applied while the signal data value is currently non-zero. Is it not better to apply (register) the changes during zero or near-zero signal data values? After all, some electronic systems employ it: http://en.wikipedia.org/wiki/Zero_crossing http://electronicdesign.com/analog/digital-volume-control-eliminates-zipper- noise Thanks. Tim.