[Fwd: Re: [PD-dev] pidip/live~]

[Yves Degoyon]

Christian Klippel wrote:

>hi,
>
>Am Sonntag, 23. Februar 2003 19:36 schrieb Yves Degoyon:
>
>>btw, haven't you noticed that the sound
>>is played at a weird speed ( faster that regular
>>but not resampled ?? ), i still wonder where
>>this might come from.... mm .... work ahead.
>>
>
>mostly this is because the soundcard has _not_ exactly the samplerate you 
>request it to have. for example, if you want 44.100 hz, you can get 44.116 hz 
>instead. this is because most soundcards have an independant oscillator.
>it is even possible for two soundcards of the same brand & type to have 
>different samplerates.
>
>that is, btw, the reason why you cant simply get multichannel sound by using 
>multiple soundcards .....
>
mm, i was not thinking of a soundcard problem,
since other way of playing sound files are ok,
palying at the right speed.
it's only the pdp_live~ object which produces
this effect.

>
>
>another reason might be due to the framerate of the video. samples per second 
>divided by frames per second must give a non-fractional result. otherwise you 
>would have a different number of samples each frame. most of the time this 
>doesnt bother, but some weird ntsc timing (with that 29.xxx fps) can cause 
>that too.
>
>
>
>best (and most used) solution is to split one _video_frame_ of audio into 
>several chunks (for example. pd's dsp size) and play them either seamlessy, 
>overlapping or by repeating the last & first sample to fit the needed time 
>(some kind of very cheap granular synthesis)  for one frame in corrospondance 
>with the soundcards samplerate.
>
>with no corrections to audio playback you will _always_ get out of sync to the 
>picture soon.
>

yes, i do agree on these remarks, but as the decoded audio frames
are decoded into a buffer before being played, and not played at once,
this means the audio data __within__ the buffer is already at the wong 
speed ??
how could i debug that is the real question right now....

thanks for your hints anyway,

cheers,

sevy/yves


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