Re: Latency Issue
Re: Latency Issue
- Subject: Re: Latency Issue
- From: Jeff Moore <email@hidden>
- Date: Thu, 29 Jan 2004 17:37:09 -0800
I don't know how the electrical connections in your hardware is set up,
but in most devices the hardware play through is a direct pass through
connection from the input to the output that happens before the
converters which yields essentially no latency.
In software play through, the latency (in sample frames) is determined
by the following formula (presuming the play through is happening on
the same device in the same IO proc):
Input Latency + Input Safety Offset + (2* IO buffer Size) + Output
Safety Offset + Output Latency
Even if all these factors but the IO buffer size are 0 (which is
technically impossible), it is still a lot larger than 0. Even if you
card has latency along the playthrough path, this is still probably
larger.
On Jan 29, 2004, at 4:08 PM, email@hidden wrote:
Hi all,
I have a question about the latency issue. Here is the situation:
I am developing an audio input driver for a PCI device. Due to the
hardware limitation, the dma transfer to the audio stream buffer 4K at
a time and the currentSampleFrame will be updated accordingly. I have
the ring buffer 16K large so there would be 4 DMA before reaching end
of the ring buffer. When the last DMA chunk finished by a hardware
interrupt callback, the takeTimeStamp() will be called.
When i do a software playthru test to play back the captured audio
data, i found that there are significant latency happened to the audio
signal when i compare with the hardware playthru output from my input
device. I have looked into one of the archives
http://lists.apple.com/archives/coreaudio-api/2003/Jun/17/
fismixable.017.txt memtioned here, but seems like it didn't solve the
problem. changing the setSampleLatency() value didn't seems to help.
So what's wrong with my setup and which area i should look into to fix
it?
I also found that if i do software playthru using Sequence Grabber
from QT, it would have a much larger latency when playback. Is there
something i missed in the setup? How can i correct this problem?
--
Jeff Moore
Core Audio
Apple
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