Cadence ALSA-JACK bridge: aliasing & quantization distortion

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unfa
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Cadence ALSA-JACK bridge: aliasing & quantization distortion

Post by unfa »

I've noticed that Cadence's ALSA-JACK bridge introduces bad distortion to the signal.
Screenshot
Screenshot
aloop.png (20.52 KiB) Viewed 552 times
Here's an example of a track in original shape, and played back through the bridge.
There's also some MP3 compression aftifacts (hihat) audible introduced by Soundcloud streaming, but other problems are far more audible:
Aliasing.ogg
Audio example
(120.55 KiB) Downloaded 54 times
I can hear aliasing there.
Also the lowpass-filtered bass part reveals quantization distortion. There's no high frequency content to alias there, so it must be it.

Anybody shares my experience?
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Re: Cadence ALSA-JACK bridge: aliasing & quantization distor

Post by unfa »

Thanks a bunch :D

Yes, a GUI item would be very helpful, I was sure this is a bug.
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Re: Cadence ALSA-JACK bridge: aliasing & quantization distor

Post by bazsound »

To be honest i have never noticed this and i use the alsa bridge fairly often to get karaoke tracks into ardour of youtube for doing vocal covers.

I also play stuff of soundcloud however im using a crappy onboard soundcard which may either hide it or im so used to it i dont notice it.

And not using crappy speakers either though they dont do anything about 15khz.

edit:

changed it to 4 dsp load is 25% and get clicks and glitches....
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Re: Cadence ALSA-JACK bridge: aliasing & quantization distor

Post by unfa »

I get the same clicks and glitches, sound like x-runs, but other JACK audio is free of that.

I think it's because the alsa_in/out processes are run with very high nice value, how can I change that to something normal? I'm looking into the code of the script, but can't find anyhting nice-related there.
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