Re: Audio I/O parameters

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On Sat, Jul 6, 2013 at 9:39 PM, James Stone <jamesmstone@xxxxxxxxx> wrote:
> On Sat, Jul 6, 2013 at 9:36 PM, James Stone <jamesmstone@xxxxxxxxx> wrote:
>> On Sat, Jul 6, 2013 at 3:41 PM, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote:
>>> On Sat, 6 Jul 2013, James Stone wrote:
>>>
>>>> The output when I try to start jack with 128 frames/period is:
>>>>
>>>> /usr/bin/jackd -dalsa -r44100 -p128 -n2 -D -Chw:USB,0 -Phw:USB,0 -I512 -O512 -S
>>>> jackdmp 1.9.9.5
>>>> Copyright 2001-2005 Paul Davis and others.
>>>> Copyright 2004-2012 Grame.
>>>> jackdmp comes with ABSOLUTELY NO WARRANTY
>>>> This is free software, and you are welcome to redistribute it
>>>> under certain conditions; see the file COPYING for details
>>>> no message buffer overruns
>>>> no message buffer overruns
>>>> no message buffer overruns
>>>> JACK server starting in realtime mode with priority 10
>>>> audio_reservation_init
>>>> Acquire audio card Audio0
>>>> creating alsa driver ... hw:USB,0|hw:USB,0|128|2|44100|0|0|nomon|swmeter|-|16bit
>>>> Using ALSA driver USB-Audio running on card 0 - Focusrite Scarlett 2i4
>>>> USB at usb-0000:00:12.2-3, high speed
>>>> configuring for 44100Hz, period = 128 frames (2.9 ms), buffer = 2 periods
>>>> ALSA: final selected sample format for capture: 32bit integer little-endian
>>>> ALSA: use 2 periods for capture
>>>> ALSA: final selected sample format for playback: 32bit integer little-endian
>>>> ALSA: use 2 periods for playback
>>>> ^CJack main caught signal 2
>>>>
>>>> ..the device is unusable with the lights flashing on and off. Jack
>>>> then shuts down as seen above.
>>>>
>>>> At 256 frames/period it starts OK.
>>>
>>> What happens if you run JACK with input only, no audio out?
>>>
>>> Alan Stern
>>>
>>
>> It works fine with both input only or output only - down to 16
>> frames/period. At 8 frames/period it shows the same behaviour as at
>> 256 frames/period in duplex - but that is a ridiculously low latency
>> of 0.2ms, so hardly surprising it won't work.
>>
>> I have now got an error message when jack fails to start in duplex mode:
>>
>> ALSA: prepare error for playback on "hw:USB,0" (Protocol error)
>> JackAudioDriver::ProcessAsync: read error, stopping...
>>
>> James
>
> Sorry - slight misinformation there. I can go down to 16 frames/period
> for capture only, but for playback only, it will only go down to 128
> frames/period. Anything lower:
>
> /usr/bin/jackd -dalsa -r44100 -p64 -n2 -Phw:USB,0 -I512 -O512 -S
> jackdmp 1.9.9.5
> Copyright 2001-2005 Paul Davis and others.
> Copyright 2004-2012 Grame.
> jackdmp comes with ABSOLUTELY NO WARRANTY
> This is free software, and you are welcome to redistribute it
> under certain conditions; see the file COPYING for details
> no message buffer overruns
> no message buffer overruns
> no message buffer overruns
> JACK server starting in realtime mode with priority 10
> audio_reservation_init
> Acquire audio card Audio0
> creating alsa driver ... hw:USB,0|-|64|2|44100|0|0|nomon|swmeter|-|16bit
> Using ALSA driver USB-Audio running on card 0 - Focusrite Scarlett 2i4
> USB at usb-0000:00:12.2-3, high speed
> configuring for 44100Hz, period = 64 frames (1.5 ms), buffer = 2 periods
> ALSA: final selected sample format for playback: 32bit integer little-endian
> ALSA: use 2 periods for playback
> ALSA: poll time out, polled for 2176094 usecs
> JackAudioDriver::ProcessAsync: read error, stopping...
>
> This is a definite reduction in performance compared to earlier kernels.
>

Some further info - on 3.5.0-28, I can start jackd in playback only
with 8 frames/period, and capture only at 16 frames/period.

James
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