Re: Latency Issue
Re: Latency Issue
- Subject: Re: Latency Issue
- From: Stefan Werner <email@hidden>
- Date: Fri, 30 Jan 2004 10:07:38 +0100
Hi,
On Jan 30, 2004, at 7:00 AM, email@hidden
wrote:
For the software playthrough testing i have done. I used my audio
driver as input device and the build-in audio driver (system speaker)
as an output device. I have found that the audio come out from the
system speaker was around 300 msec behind the audio comes from the
hardware playthrough.
In that case, you also have to consider that the default output adds
latency too. What program did you use to test the latency? Usually,
there's an additional buffer between your application and the HAL, and
I think the default for most built-in sound hardware is 512 frames.
From what i understand, that 300 msec delay would comes from :
Input Latency + Input Safety Offset + (2* IO buffer Size) + Output
Safety Offset + Output Latency
You have to add the applications themselves to that equation. It's the
best to use a test application that lets you adjust the buffer size or
to write your own throughput application.
therefore, most of the delay comes from the IObuffer size then? and
the way to minimize the latency is the adjust IObuffer size only?
That and the safety offset. If you do the math, 2*4096 samples at 48kHz
are about 170ms, so this seems to be where most of your ~300ms come
from.
Also for the input latency parameters specified in the
setInputSampleLatency(), does it means the hardware latency for
passing through the converter and before DMA process?
Yes, with setInputLatency() you tell the HAL what latency your hardware
itself has. Applications can use that to compensate latency, e.g. for
synching audio with video.
hope this helps,
Stefan
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