[pulseaudio-discuss] Merging soxr

[Alexander E. Patrakov]

07.01.2015 15:14, Alexander E. Patrakov wrote:
> I will retest with qemu (via its alsa backend) later today.

Done, both for "pa" and "alsa" backends. I must say that soxr-based 
resamplers break a configuration that worked fine (except the initial 
period of several seconds) with speex-float-5. Namely, after some 
seconds of initial crackling (which is a KVM limitation), speex-float-5 
produces clear sound for at least 5 minutes. soxr-based resamplers 
produce a constant stream of underruns.

The (insane) configuration below is the one required to get 
somewhat-nonbroken audio from KVM running a Mac OS X guest. You cannot 
increase latency here, because we need to emulate the sound card driven 
by Mac OS X in their equivalent of tsched mode (which cannot be switched 
off) with quite strict scheduling safety margin (which cannot be 
configured). I.e., increasing latency would lead to qemu-level underruns 
where it fails to copy the sound data from the memory belonging to the 
emulated device in time and copies a piece of silence instead.

Inside the guest, an mp3 file (44100 Hz stereo) was played using afplay 
through the VoodooHDA driver. On the host (which has an onboard 
snd-hda-intel card), pulseaudio was restricted to 48000 Hz using 
daemon.conf to force resampling.

#!/bin/sh

export QEMU_AUDIO_DRV=pa
export QEMU_PA_SAMPLES=440
export PULSE_LATENCY_MSEC=8  # gets clamped to 2 ms for unknown reason
export QEMU_AUDIO_TIMER_PERIOD=1000

nohup \
flock -n hda.dsk \
         qemu-system-x86_64 -enable-kvm -m 2048 -cpu core2duo -smp 2 \
         -machine q35 \
         -vga std -sdl \
         -soundhw hda \
         -usb -device usb-kbd -device usb-mouse \
         -device isa-applesmc,osk="...(c)AppleComputerInc" \
         -smbios type=2 \
         -device ide-drive,bus=ide.2,drive=MacHDD \
         -drive id=MacHDD,if=none,file=hda.dsk \
         -netdev user,id=hub0port0 \
         -device virtio-net,netdev=hub0port0,id=mac_vnet0 \
         -monitor stdio \
</dev/null >/dev/null 2>&1 &

(search Google for OSK0 and OSK1, the command line was mostly 
copy-pasted from 
http://blog.ostanin.org/2014/02/11/playing-with-mac-os-x-on-kvm/ )

Also, with PulseAudio forced to 44.1 kHz, FooBar2000 v1.2 (which uses 
DirectSound and thus, by default, resamples everything to 48 kHz) just 
plays silence (with a neverending stream of underruns in pulseaudio log) 
over soxr-vhq and works fine over speex-float-5. soxr-hq and soxr-mq 
also work fine with wine.

If you don't have Mac OS X, you can also reproduce the first bug (which, 
BTW, also applies to -mq and -hq) with paplay:

paplay --latency-msec=8 any-44100hz-stereo-file.flac

Note again: there are constant underruns in this case in the pulseaudio 
log, which are not present with speex-based resamplers.

Or you can just dismiss the issue, because the testcases just request 
latency that cannot be satisfied with soxr.

-- 
Alexander E. Patrakov