[oss-devel] Just an idea

[Hannu Savolainen]

Zakhar Levchenko kirjoitti:
> 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?
Correct.

Best regards,

Hannu