[Portaudio] Lowest possible latency

[Reid Bishop]

All,

 

My Windows 7 64bit Dell DOES INDEED support 24bit capture in my application
when using WASAPI.  I have a RealTek HD audio chipset, and this supports
192khz sampling at 24 bits, both input and output (full duplex).  Dmitri, I
saw some posts earlier that your fixes to the implementation do not support
Event driven mode?  I beg to differ- that is what you fixed and checked in
to help me get around my problems.

 

The RealTek Audio control panel does seem to indicate that 24 bit is not
"supported" for Line In, so I set it to its max of 16 bit.  My output,
however, is set for 24 bit, as is my application.  Using Event driven shared
interface, I'm having no difficulty using what appears to clearly be 24 bit
(my application makes it easy to tell whether we are only using 16 bit).  I
hope to do some latency tests later this month (I need to re-wire my channel
configuration code to work with this 7+1-channel device to get to a point
where I can actually measure latency).   My gut feel is that this WASAPI
implementation has far lower latency than my M-Audio ASIO implementation- I
just cannot yet take measurements to back that claim up.

 

Let's not make assumptions about how WASAPI behaves quite yet, and go off
making lots of code changes!

 

-Reid-

W0CNN

CNNSDR Development

 

  _____  

From: portaudio-bounces at music.columbia.edu
[mailto:portaudio-bounces at music.columbia.edu] On Behalf Of c319chris at aol.com
Sent: Thursday, June 10, 2010 3:32 AM
To: portaudio at music.columbia.edu
Subject: Re: [Portaudio] Lowest possible latency

 

Well Ross, now I agree with you that ASIO is the superior API. It turns out
that WASAPI does not do 24-bit capture according to Dmitry.

I have an EMU 0404 USB interface which delivers, by actual test, a
signal-to-noise ratio of 110.4 dB A-weighted, BUT it only achieves this
lovely S/N using the EMU ASIO driver. All other Windows drivers deliver
90-some-odd dB of S/N, even in 24-bit mode, leading me to suspect they are
only doing 16-bit samples and padding them to 24 bits. I suspect the EMU
ASIO driver is doing actual 24-bit sampling. At 6 dB per bit, 16 bits are
capable of 96 dB and 24 bits capable of 144 dB.

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