Old 01-01-2010, 01:28 PM   #1
Fabian
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Default 512 samples buffer, is that 17 ms or 36 ms?

Following Lokasennas great thread on measuring and compensating for interface latency (http://forum.cockos.com/showthread.php?t=48884) I decided to measure my own interface. I have a Lexicon Lambda interface that I usually drive with ASIO4ALL, but there is also a native Lambda ASIO driver. When comparing these two drivers I stumbled on something that I cannot get my mind around. Hopefully someone here can help out...

Reaper reports in the top right corner, asio buffer and approximate latency times. I cannot get to really understand those numbers. Here is what it shows me for different buffer settings:

44.1 kHz, 24 bit wav

ASIO4ALL
128 samples buffer, ~8.6/8.6 ms
256 samples buffer, ~11/11 ms
512 samples buffer, ~17/17 ms

Lambda ASIO
128 samples buffer, ~9.9/9.9 ms
256 samples buffer, ~18/18 ms
512 samples buffer, ~36/36 ms

So, 512 samples buffer is either 17 ms latency or 36 ms... which is it?

Even more... if I do the calculations... for 44.1kHz sampling, there are 44.1 samples/ms, so 512 samples would correspond to (512/44.1 = ) 11.6 ms! Now I'm even more confused...

Furthermore, that double buffer would give double latency time, as in the Lambda ASIO case, seems reasonable. But why would this not be the case with ASIO4ALL?
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Old 01-01-2010, 01:47 PM   #2
Diogenes
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Many manufacturers build in additional buffering for their interfaces/drivers. Especially the USB/FW interfaces. Maybe that's what you see with the Lambda's native driver?

D

PS Try a loopback test and see what it REALLY is...
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Old 01-01-2010, 01:53 PM   #3
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I'd suspect this is because a native ASIO driver can hand some of the work to be done to the hardware it is written for, whereas ASIO4all has to use what windows has to offer. On my system e.g. I get 13/13 ms with native ASIO drivers, but 11/11 with ASIO4all (@44,1 kHz/512), which seems to negate what I just wrote, but ASIO4all doesn't work here very well. I've got dropouts (pauses) of, say 1/10 of a second once or twice a minute.




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Old 01-02-2010, 03:15 AM   #4
Fabian
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Thanks for the replys, guys.

I think I see now where I err... I thought Reaper calculated the ms latency from the buffer size (and I guess I wasn't clear on that being my problem). But as I understand it from what you say, the driver informs Reaper of both the ms latency and the buffer size, and these two need not match in the way I calculated, since internal buffers and what-nots may come into play.

Yes, I did loop-back tests (as per Lokaseenas thread) and I got the following results.

ASIO4ALL:
128 samples buffer, 774 samples latency, 18 ms
256 samples buffer, 1030 samples latency, 23 ms
512 samples buffer, 1542 samples latency, 35 ms

Lambda ASIO:
10 ms buffer (128 spls), 933 samples latency, 21 ms
18.7 ms buffer (256 spls), 1700 samples latency, 38 ms
36.1 ms buffer (512 spls), 4296 samples latency, 97 ms

For Lambda ASIO the buffer is set in ms, and the sample count within parenthesis is as reported from Reaper.

One thing to note, the "samples latency" numbers for ASIO4ALL are related to the set buffer size as (2 x "samples buffer" + 518). No such relation can be (easily) found for the numbers reported for the Lamda ASIO driver.

And BTW, this makes me understand why I like the ASIO4ALL driver better than the Lambda ASIO...
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