I ran some more Audacity latency tests today, this time using two Raspberry Pi 4s with the latest Raspbian (no tuning). Long story short is the results were not much different from OSX:
|Focusrite 2i2 gen2||7ms (2ms buffer)|
|Focusrite 2i2 gen3||7ms (2ms buffer)|
|Sabrent USB||12ms (5ms buffer)|
|Ugreen USB||12ms (5ms buffer)|
|Corsair Headset||43ms (10ms buffer)|
I used lsusb to confirm that the Sabrent and Ugreen devices do use the same chipset: both reported “C-Media Electronics, Inc. Audio Adapter (Unitek Y-247a)”.
I also tried running a few round-trip tests over network using Mumble. I configured two identical Pi’s, connected via ethernet to the same LAN. One of them had a 3.5mm loopback cable connecting its input to output. I used the built-in recording capability of the Mumble client on the other Pi to create recording tracks which I analyzed using Audacity. I used the minimum (10ms) buffer with the highest quality settings.
I tested with both Pis using Sabrent USB devices, and then with both Pis hooked up to Focusrite 2i2’s (gen2 and gen3). I tested each of these combinations using both a Murmur server on my LAN, and using a Murmur server on an EC2 VM in the us-west-1 region. I have a 10-20ms round-trip ping to this server from my home network via Comcast.
Here are the results:
|Sabrent USB (identical)||LAN (<1ms ping)||92ms|
|Focusrite 2i2 (gen2, gen3)||LAN (<1ms ping)||125ms|
|Sabrent USB (identical)||EC2 (10-20ms ping)||125ms|
|Focusrite 2i2 (gen2, gen3)||EC2 (10-20ms ping)||196ms|
Note this was a full round-trip test, so the one-way latency would be roughly half these measurements. Even so, these were pretty disappointing results given our target of less than 50ms. In case you are wondering what this latency sounds like, here are the corresponding WAV files:
One thing you’ll notice is that the Focusrite recordings seem to sound much better than the Sabrent. I thought this might be because of the $90+ price difference, but it didn’t sound nearly as bad just recording and playing back directly using Audacity. It’s quite possible that the 3.5mm loopback cable I have is bad, or some other randomness is at play here.
Long story short, this seems to confirm that even Mumble’s “ultra-low latency” is not an option for live performances. Next I’ll be trying out JackTrip, which seems a lot more promising.