[PlanetCCRMA] delay in general

"Alexander Carôt" alexander_carot@gmx.net
Tue Jan 24 03:12:01 2006

> Good luck and let us know if you succeed.

Hi Luis,

thanks for the response ! I followed your link and noticed that you
experience the same in/out-delay (~ 15ms) with USB-soundcards. I'm a little
surprised because Emagic claims to reach delay in the area of 6ms under
Windows (ASIO) but I'm wondering if it's true.

Actually it seems to me that the delay details are a pretty "wishy-washy"
issue - some questions regarding this :

1.) Can anyone recommend literature/links for soundcard DSP and    
    construction ?
2.) summing up the delay types there's 

ADC-delay, blocking-delay, DAC-delay

For the caputure process it's ADC+blocking (for 48kHz, 256 samples/frame = 
1ms (ADC)+ 5.6ms (blocking) = 6,6ms 

Assuming that the captured block would be inserted into the playback buffer
at the right time it wouldn't take any delay for playback process, right but
since it's a problem to get the buffers in sync it typically takes another
6,6ms to play it back, right = so altogether = 2 * 6,6ms = 13,2 ms
in/out-delay. Is that correct ?

3.) Has anyone information about the communication layer USB-audio puts on
top of the PCI-bus and how much delay it takes ? In other words : Can a USB
device ever reach latencies like PCI-devices ? Also : I need an excellent
external device for my laptop. If USB isn't suitable what's the alternative
(Firewire, external PCI-Cards : which ones ?).

Thanks in advance

-- A l e x 

Dipl.-Ing. Alexander Carôt
Email : Alexander@Carot.de
Tel.: +49 (0)177 5719797

phd-candidate at www.isnm.de

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