ASR Loop Glitches

[David Battino]

Hello. Seems like ASR looping stopped working in the beta VCA firmware. Loop points didn't persist in the editor. They changed to 1 and 2. 

Reverting to 3.8.3 fixed that, but pitch-interpolating an ASR loop isn't working. The root note loops cleanly, but the interpolated ones glitch. I'm using a 44.1kHz, 24-bit stereo WAV file (attached) set to loop between the middle and very end.

C3 pitch

13708 start

28708 end

Also, the Read Me says shift-command-click, but for me it was shift-option-click.

Thanks!

[WVR Audio]

Thank you David, I will address this ASAP.

I made some changes recently when someone reported that it was too easy to enter glitchy loop points (ex. 0) and its possible I messed some stuff up.

[WVR Audio]

Just to confirm, this VCA behaviour does not apply to ASR loops, because the ASR loop already has this built in, and also because it would be incredibly hard to code haha.

[David Battino]

Thanks, Andrew. Interestingly, the WAV file I attached was a commercial one and had loop points set in the metadata. When I opened it in Zynaptiq Loop Editor 2, I saw the start and end points filled in.

[WVR Audio]

Ok there is a patch available that I think addresses both bugs.
https://github.com/marchingband/wvr_binaries/blob/main/wvr_vca/wvr_usb_patch.ino.bin

[David Battino]

Finally had a chance to try 3.8.4; the loop point is interpolating now. Thanks! I still hear a faint click on some transposed notes. In earlier looping tests, I noticed Ogg files looped more cleanly than WAVs or MP3s. Might try Ogging some of these sustain loops.

[WVR Audio]

I am worried that pitch shifting loop points is mathematically imperfect ... I can imagine that after a shift, there may no longer be a zero crossing that falls on a sample boundary. After a pitch shift, the algo usually has to round the sample position for the loop points, it is rarely a whole integer. It seems to me that this indicates that it would no longer fall on a zero crossing, and in the worst cases (rounding from N.4 to N.0 for the loop-start, and N.6 to (N+1).0 for the loop-end, for example) perhaps this imperfection is producing a click. If this is the case I'm not sure a fix would exist.

[David Battino]

FWIW, I tried Ogg versions of the loops and they were glitchier than my WAVs. But I think the interpolation works well enough. In most cases, there were tiny clicks; only a few thuds. I've found zero crossings alone aren't enough to guarantee a smooth loop; you sometimes have to add crossfading. For super-smooth sustained sounds, I'll probably loop the whole file or use one sample per note. 

Thanks again for the quick turnaround. I'm planning to perform with my WVR at Knobcon next weekend.

[WVR Audio]

Interesting ... I am honestly not sure why there would be a difference using wav or ogg ... both get converted to WAV in the browser before any modifications occur.

I am not familiar with Knobcon but that is so exciting!! good luck! and please share some videos if you can!!!

[David Battino]

Huh. If they’re both WAVs, I wonder if one file had different metadata. The Sparkfun Tsunami won't even play WAVs that contain metadata; I have to strip it with a special program. It loops beautifully, though! ;-)

I've interpolate-loaded a number of ASR files now. (Back on the 3.8.4 VCA firmware because I wanted the attack control for my performance.) Sometimes individual interpolated notes will get corrupted or forget their loop points. I'll try loading WAVs with the metadata removed.

The difference I hear between Ogg and WAV is subtle — a tiny click on the WAVs, and if I trigger both at once, they eventually drift apart. As a comparison, I tried the same loop as an MP3 and a Compuphase-padded MP3. Those were quite bumpy. I can send you my test files if you like.

Thanks again! I think the Knobcon performance will be YouTubed. My duo is called The Palindrones. Loading some droney sounds into the WVR now....

[WVR Audio]

The metadata is removed in the browser, so that isn't a factor.

Did you see this firmware? It is VCA firmware with the ASR interpolation patch.

"Sometimes individual interpolated notes will get corrupted or forget their loop points."

Gah I wonder if I have got something wrong in the design ... this should of course not happen ... any way for me to reproduce?

[WVR Audio]

regarding the Compuphase-padded MP3, this may not work for WVR. When any file is loaded into the web UI, it is immediately converted to a PCM wav file. I can't tell exactly what this CompuPhase tool does, but is seems likely that it works with mp3 encoding algo, so it may be counter productive to then convert them back to .wav, it may cancel out the effectiveness of the CompuPhase tool. I can't be sure, but that is my intuition.

[David Battino]

Andrew, you mentioned the browser converts all audio files to WAV before transferring them to WVR. Does it change the bit depth and sample rate? If so, I'd think we could save time by first converting our source files to the native format. (I've gotten used to doing that on the Tsunami, which supports only 16-bit, 44.1kHz input files — and no metadata!)

[WVR Audio]

Yes it converts all files to stereo 44.1 16bit, but it doesn't take any time, it has to do a rendering pass anyhow, so no way to speed anything up that I know of.