Re: [Qemu-devel] [PATCH] hw/usb/dev-audio.c: make USB audio card sound perfect

[Programmingkid <programmingkidx@gmail.com>]

On Oct 16, 2015, at 8:15 AM, Stefan Hajnoczi wrote:

> On Tue, Sep 22, 2015 at 07:32:01PM -0400, Programmingkid wrote:
>> The USB audio card would not play audio well because its buffer was too small. 
>> Increasing it made it play perfectly. All the crackling and dropouts are gone.  
>> 
>> Signed-off-by: John Arbuckle <programmingkidx@gmail.com>
>> 
>> ---
>> This patch was tested on qemu-system-ppc running Linux and qemu-system-i386
>> running Windows XP. Windows XP sound output thru the USB audio card sounded
>> perfect. Linux did improve in sound quality, but it still wasn't perfect. I
>> think there are problems with the hcd-ohci.c file. The Mac OS 10.2 guest in 
>> qemu-system-ppc did not play sound due to USB issues unrelated to this patch. 
>> 
>> hw/usb/dev-audio.c |    3 ++-
>> 1 files changed, 2 insertions(+), 1 deletions(-)
>> 
>> diff --git a/hw/usb/dev-audio.c b/hw/usb/dev-audio.c
>> index f092bb8..e4e4989 100644
>> --- a/hw/usb/dev-audio.c
>> +++ b/hw/usb/dev-audio.c
>> @@ -88,6 +88,7 @@ static const USBDescStrings usb_audio_stringtable = {
>> #define USBAUDIO_PACKET_SIZE     192
>> #define USBAUDIO_SAMPLE_RATE     48000
>> #define USBAUDIO_PACKET_INTERVAL 1
>> +#define BUFFER_MULTIPLIER        32
>> 
>> static const USBDescIface desc_iface[] = {
>>     {
>> @@ -664,7 +665,7 @@ static const VMStateDescription vmstate_usb_audio = {
>> static Property usb_audio_properties[] = {
>>     DEFINE_PROP_UINT32("debug", USBAudioState, debug, 0),
>>     DEFINE_PROP_UINT32("buffer", USBAudioState, buffer,
>> -                       8 * USBAUDIO_PACKET_SIZE),
>> +                       BUFFER_MULTIPLIER * USBAUDIO_PACKET_SIZE),
> 
> I'm not familiar with the code but I guess this also increases audio
> latency by a factor of 4 (8 -> 32).

Didn't hear any problems. When I tried it out. 

> Gerd might have an opinion on whether that is okay or not.

I doubt it. I don't even think he is with QEMU anymore. He doesn't
even answer simple emails. He probably stopped working on
QEMU. I do think it is time to add another USB maintainer.