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Re: [Sc-devel] scsynth -L option


quite frankly, I dont know exactly what the parameter does. As portaudio is a platform independent API it is up to the various implementation to put this value into context. It is, however, not the hardware buffer size (which can be assigened separately).

The proposed -L switch would provide access to the PaTime PaStreamParameters::suggestedLatency (from the docs):

The desired latency in seconds. Where practical, implementations should configure their latency based on these parameters, otherwise they may choose the closest viable latency instead. ... Actual latency values for an open stream may be retrieved using the inputLatency and outputLatency fields of the PaStreamInfo structure returned by Pa_GetStreamInfo().

For Windows MME drivers the default suggested latency is up to 0.2 sec while the buffer size is still 64 samples. Maybe Ross can shed some light on this.


ronald kuivila wrote:
Hi all,

Maybe a little explanation is in order. There are several different issues parameters involved in system latency:

	blockSize				-z option
	hardware buffer size 		-Z option
	Server object latency		language side parameter that can be tuned

Right now, if the hardware buffer size is bigger than blockSize, untimestamped messages are processed on the next hardware buffer rather than the next sample block. (This is the issue Alberto mentioned on the list a while ago.)

The Server object latency imposes a delay that should be larger than the largest delay associated with hardware buffer size and UDP transmission. This will guarantee accurate timing. It can be altered without rebooting the server.


On Mar 4, 2008, at 5:01 AM, Stefan Kersten wrote:

On 29.02.2008, at 14:59, Christopher Frauenberger wrote:
now that version 3.2 is launched, I would commit the change proposed.
It essentially introduces a -L switch to scsynth when compiled with
port-audio to specify a preferred latency. This is important as the
suggested latency (especially on Windows) is sometimes really high
(0.2 sec) and could be reduced by the user for time-critical things
through the server options.
shouldn't the hardware buffer size -Z option be used for specifying
the latency? scsynth seems to be competing already with csound in
terms of command line options ;)


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