ALSA backend distorts low frequencies while JACK doesn't (suspect: ALSA to JACK bridge)

[unfa]

Listen to these samples:
http://unfamusic.com/5h1+/samples.zip

I've played the original sample via Sound File Processor. It sounded different - I heard high frequency content that was not present in the original sample.

I've noticed I have ALSA back-end selected. I changed to JACK and re-tried. The distortion was gone.

I was using JACK anyway so the ALSA back-end was bridged back to JACK. And then - the bass sample had additional high frequency content that must have been created by some kind of aliasing or bad interpolation.

I've captured the distorted sample with jack_capture program.

What's strange - the distortion also appears in the rendered project, however it sounds different.

I've tried using ALSA directly (with no JACK running) and the distortion is gone.

So it's probably ALSA-to-JACK bridge that adds this distortion, however - why does it affect the rendered output? THIS is what bothers me most. Why does dummy back-end allow rendering then?
How does the rendering work? Maybe the signal from LMMS to WAV file passes through something unneeded half-way through?

Anyway - we should notify whoever is working on ALSA-JACK bridge about this, maybe it's their bug.

[zonkmachine]

The first thing I think of with distortion is pulseaudio.

I've noticed I have ALSA back-end selected.

Pulseaudio can interfere anyway. Have you specifically stated for LMMS which soundcard to use?
http://lmms.sourceforge.net/wiki/index.php/Troubleshooting#I_get_lots_of_latency_.28lag.29_when_playing_instruments_in_LMMS

[unfa]

I played the same sample with SOX via PulseAudio and LMMS.

LMMS distorts sound, while SOX doesn't.

Same with SDL for LMMS.

What seems like direct ALSA usage (LMMS hangs up for a while on start, and
hangs for good if I want to open the preference dialog so I'm not sure)
don't distort the sound. PA was down, and JACK was down too, and after
launching JACK, LMMS opened much faster and was distorting the sound going
throug PulseAudio with ALSA "default" setting active. So maybe it's the way
LMMS talks to PulseAudio?

2014-02-05 Oskar Wallgren notifications@github.com:

The first thing I think of with distortion is pulseaudio.

I've noticed I have ALSA back-end selected.

Pulseaudio can interfere anyway. Have you specifically stated for LMMS
which soundcard to use?

http://lmms.sourceforge.net/wiki/index.php/Troubleshooting#I_get_lots_of_latency_.28lag.29_when_playing_instruments_in_LMMS

Reply to this email directly or view it on GitHubhttps://github.com//issues/276#issuecomment-34192272
.

Tobiasz unfa

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[diizy]

Does this still happen with the latest version?

[tresf]

Consolidated to #1467, "Better JACK support" issue.

This bug may not be directly related to JACK, but rather to the ALSA-to-JACK bridge. Please reopen if you feel it needs to be split off onto its own bug report again.