Hannu Savolainen wrote:
>Zakhar Levchenko wrote:
>> Now when a device is opened with open() call OSS driver automatically
>> sets some default sample rate (usually 48000). I think it is good to have
an option to disable setting default sample rate when opening a device.
>> This may be some compile option or an
>> option from some configuration file (I don't insist that this should
>> be done by default, it should be done for those who absolutely need
>> it). It may be useful sometimes.
>> For example, on my sound card (ESI Juli@) changing sample rate causes an
audible click (I believe it is not an OSS driver fault but some hardware
limitation, the same effect is observable on WinXP by the way).
>> This effect may be noticeable when a series of audio file is
>> played. Suppose all files are in 44100, and
>> an audio player opens a device for each file (most common situation), so
for each file sample rate is set two times (48000 and 44100 then). So when
each file is started a click is audible.
>> But actually there is no much sense to switch sample rate when a
>> device is opened.
>> In this case just previously set sample rate will be used, and it is
desirable sometimes. The idea is that changing sample rate should be done
only when it is absolutely necesserily.
>> Anyway, audio applications need to set sample rate explicitly with
SNDCTL_DSP_SPEED call. I myself use OSS
>> compiled
>> with my own modification of audio_core.c where line that sets a default
sample rate when
>> a device is opened
>> is removed, and everything works fine. So it is not problem for me.
>> I just think that this may be useful for other people (for example for
>> other owners of ESI Juli@ card) who may experience similar problems.
>> Does anybody else think that it is worthy idea?
>Nothing is supposed to get changed in the hardware registers at the
>moment when open() or SNDCTL_DSP_SPEED is called. The hardware will be
>programmed to the selected sampling rate just before the moment when
>playback/recording is actually started. So if several 44100 files are
>played in row then the device should stay at 44100 even open() changes
>the rate to 48000.
>
>If the hardware gets reprogrammed to 48000 between the files then there
>is a bug in the driver.
>
>Best regards,
>
>Hannu
I see. Hardware is directly reprogrammed in
envy24ht_set_rate which is called from oss_audio_set_rate. So this
should be done in envy24ht_prepare_for_input and
envy24ht_prepare_for_output
instead? Am I correct?
Regards,
Zakhar Levchenko
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