for my custom Zynthian I am evaluating to replace the current audio hat with an USB audio card with 5pin MIDI connectors
as I read a comment of Jofemodo that latency could increase with USB cards,
I ask you if you could suggest me items that keep the latency low, based on your use
There isn’t a substantial issue with USB soundcards. The very cheap ones with small hardware buffers require large buffer settings which increases latency but most reasonable quality USB soundcards are fine for most users. There are some that have more support in zynthian. (Check the list of configuration options in webconf HARDWARE → Audio.
Focusite are good and I like my Tascam US-1608 but Behringer are quite a good option too.
like Behringer U-Phoria UMC204HD?
Indeed! I have the UMC1820 which works well. I also have the Tascam US-1820 which I prefer. (It has DSP with compression and 4-band EQ on every input.) Others have liked the Behringer U-Phoria UMC204HD with its 4 outputs. I prefer to increase the quantity of inputs but that really depends on your use case. (I use mine as a mixer and multitrack audio recorder.)
Yep the umc204hd isn’t bad at all, especially considering the price. Though for my use case I ran into input drought quickly (by now I need to connect 3 stereo inputs and a 4th is on the horizon once I travel to France this summer) so I had to upgrade (I chose a focusrite 16i16).
It’s worth considering if you plan to aquire some equipment that needs its own inputs (eg no USB audio or USB audio noisy) so you don’t make my error and buy something that quickly becomes underequipped for your needs. I use the umc204hd as a pure 1 stereo in so it’s not completely wasted. I’m also already eyeing the Behringer 1820 because it can be used to add 8 inputs to the focusrite…
USB latency for audio depends directly on the way the manufacturer has implemented the USB communication stack, processor model, etc…
Many chinese low-cost products use a very old design, based on Cypress (or equivalent) USB chip, with a 8-bit CPU core… And as @Riban says, the problem is that require extremely large buffers if you want to avoid any buffer underrun (impacting negatively the latency
USB sound cards using XMOS XU216 processors are generally very good (but with a price on the higher end…)
A few years ago, I made a custom USB sound card based on TI PCM2901 chip, and I was simply baffled by the performances, as I was able to reduce the buffer size to very small value without audio glitches. My assumption was that the PCM2901 does not use an internal processor to decode the USB audio stream, it does it with a dedicated circuitry so the latency is kept to the strict mimimum
Benoit
I run my Tascam US-1608 with 11ms (software) latency which works well for my rock and blues guitar style.