Subject: low-latency audio I/O for Windows: a report From: "Freed, Dan" <DFreed@xxxxxxxx> Date: Mon, 3 Dec 2007 14:16:16 -0800 List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY>Dear Auditory List Members: In October I posted a request for information about low-latency audio interface devices for use with Windows. I received many helpful responses. Over the last two months I've had the opportunity to acquire several devices and measure their latencies. Since latency information is generally not reported (or is incorrectly reported) in manufacturer specifications, I'm posting my measurement results here. By "latency", I mean the total end-to-end delay imposed by the device and its driver, from analog input to analog output. This doesn't include any additional delay imposed by the software signal processing (filter group delay, FFT blocking delay, etc.). Latency was measured by presenting a pulse train to the analog input, viewing the analog input and output on a dual-trace oscilloscope, comparing the traces, and visually estimating the delay. Tests were performed under Windows XP. The PC was running a simple 1-channel input-to-output copying program that accesses the device through the ASIO driver interface. Each device was tested at multiple sampling rates. At each sampling rate, testing was performed using the shortest buffer length that the device supports for that sampling rate, so the measurements are best-case results. Results are shown below. Sampling rates are in kHz, latencies are in ms. Buffer length in samples is shown in parentheses. Note that latencies under 3 ms are achievable at the higher sampling rates with some devices. EDIROL UA-1EX [USB device, $80] 32 kHz: 14.2 ms (96) 44.1 kHz: 11.5 ms (96) 48 kHz: 12.0 ms (112) M-AUDIO FIREWIRE SOLO [FireWire device, $172] 44.1 kHz: 9.0 ms (64) 48 kHz: 8.2 ms (64) 88.2 kHz: 6.5 ms (64) 96 kHz: 6.1 ms (64) ECHO AUDIOFIRE 4 [FireWire device, $300] 32 kHz: 8.0 ms (32) 44.1 kHz: 6.0 ms (32) 48 kHz: 5.5 ms (32) 88.2 kHz: 3.6 ms (32) 96 kHz: 3.4 ms (32) RME FIREFACE 400 [FireWire device, $1000] [at some sampling rates, 48-sample buffer caused bus errors, so used 64-sample instead] 32 kHz: 10.4 ms (64) 44.1 kHz: 6.6 ms (48) 48 kHz: 6.0 ms (48) 64 kHz: 6.2 ms (64) 88.2 kHz: 4.5 ms (64) 96 kHz: 4.2 ms (64) 128 kHz: 4.2 ms (64) 176.4 kHz: 2.9 ms (64) 192 kHz: 2.5 ms (48) M-AUDIO DELTA 44 [PCI device, $200] 16 kHz: 16.2 ms (64) 22.05 kHz: 11.7 ms (64) 24 kHz: 10.7 ms (64) 32 kHz: 8.1 ms (64) 44.1 kHz: 5.9 ms (64) 48 kHz: 5.5 ms (64) 88.2 kHz: 3.0 ms (64) 96 kHz: 2.7 ms (64) ECHO LAYLA 3G [PCI device, $500] 32 kHz: 8.8 ms (64) 44.1 kHz: 6.4 ms (64) 48 kHz: 5.9 ms (64) 64 kHz: 4.2 ms (64) 88.2 kHz: 3.1 ms (64) 96 kHz: 2.8 ms (64) RME MULTIFACE II + HDSP PCI [PCI device, $1049] 32 kHz: 6.5 ms (32) 44.1 kHz: 4.7 ms (32) 48 kHz: 4.3 ms (32) 64 kHz: 3.8 ms (32) 88.2 kHz: 2.8 ms (32) 96 kHz: 2.5 ms (32) Caveat: running at high sampling rates with short buffer lengths increases the risk of dropouts. I did some limited listening tests in all of the above testing conditions and never heard any dropouts, but I offer no guarantees. I'd be happy to answer any questions about my measurements. I hope this information is useful. Dan Freed Senior Engineer Dept. of Human Communication Sciences & Devices House Ear Institute 2100 W. Third St. Los Angeles, CA 90057 USA Phone: +1-213-353-7084 Fax: +1-213-413-0950 Email: dfreed@xxxxxxxx