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Re: [Qemu-devel] wav output sounds good - what does this mean?
From: |
Programmingkid |
Subject: |
Re: [Qemu-devel] wav output sounds good - what does this mean? |
Date: |
Wed, 9 Sep 2015 10:37:03 -0400 |
On Sep 9, 2015, at 5:17 AM, Stefan Hajnoczi wrote:
> On Sun, Sep 06, 2015 at 04:53:29PM -0400, Programmingkid wrote:
>> I have been working on making the sound output from the USB sound card
>> actually sound good. When the audio is sent to CoreAudio, the sound is not
>> very good. But when I use the wav file output option, the sound in the wave
>> file sounds perfect. What does this mean?
What I meant by doesn't sound very good is that the audio has a lot of static
in it. It kind of sounds like a vinyl record being played back. There is also
this deformed audio sound. Hard to describe in words. I could send you a sample
of the audio, but I think it might be easier for you to try it yourself. If you
are on Linux, use this command to build QEMU:
./configure --target-list=i386-softmmu --audio-drv-list=alsa --enable-sdl &&
make
To test the wav output option, use this command before starting QEMU:
export QEMU_AUDIO_DRV=wav
To test out live playback, use this command before starting QEMU:
export QEMU_AUDIO_DRV=alsa
Then to use the usb audio card, just add this to the command options you send
to QEMU:
-usb -device usb-audio
or
"device_add usb-audio" in QEMU's monitor
I use qemu-system-ppc, but this problem is also present on qemu-system-i386. I
have used Windows XP, Debian Linux, and Mac OS 10.2 as a guest, and they all
have problems playing back audio using the usb sound card. So anyone of these
operating systems can be used in the guest for testing. Using a Linux guest
would probably yield better results.
My attempts to 'make' QEMU on a Linux host haven't been very good lately, so I
can't test it out right now. I probably need to reinstall Linux. It would be
interesting to see how the usb-audio card sounds for you on Linux. If you do
try, could you let us know how it sounds?
> You didn't describe or post an example of the "not very good" sound via
> CoreAudio.
>
> Perhaps QEMU is not filling playback buffers quickly enough, causing
> underruns? These are drop-outs in the audio and are caused by missing
> the real-time deadlines for filling playback audio buffers.
I was thinking it was a buffer issue also. :) Maybe increasing the size of the
buffer
would help.
>
> The wav output wouldn't have that problem since data is appended while
> QEMU is running but you only listen to it later. So the timing doesn't
> matter and it will sound fine.
>
> Another possibility is that QEMU isn't writing audio samples in the
> format that CoreAudio expects, so you hear weird artifacts.
I have tried every other format I could find. By that I mean these:
AUD_FMT_U8
AUD_FMT_S8
AUD_FMT_S16
AUD_FMT_U16
AUD_FMT_U32
AUD_FMT_S32
The best sounding one is the one that is currently being used: AUD_FMT_S16.
>
> More info is needed...
>
> Stefan
On second thought, I will send you audio samples of both live playback and wav
output in a second email.