Cheap Multichannel Audio on OS X


Recently I was looking for inexpensive (< $50) audio interfaces that provide 8 analog outputs for sound art installations and surround mixing in the studio. The search led me to “7.1 channel USB soundcards” based on the C-Media CM6206 chipset. These interfaces provide 2 inputs and 8 outputs and utilize the built-in Mac OS X “class driver”. It works as soon as you plug it in. No need to install any drivers and it should stay compatible with future OS versions. (Note that many marketers like to slap a “7.1 channel surround” label on interfaces that are actually 5.1 or less, touting magical driver voodoo to simulate the missing channels. Count the output jacks in the pictures!)

I bought 2 different CM6206 USB interfaces in 2014, the Sabrent USB-SND8 and the Diamond XS71U. Both seem to be based on a similar reference design and both are now discontinued but you can probably find them or their siblings somewhere online. (The StarTech ICUSBAUDIO7D is based on the same chipset but I haven’t personally tested it.)

Both interfaces share these characteristics:

  • All audio IO is on 1/8″ stereo jacks. They sound fine in my listening tests. There is no digital noise from unfiltered USB power, or audible hiss from the analog outputs.
  • One exception to the above is the mic inputs available on both boxes. They supply low voltage “plug-in power” for condenser mics but the gain is very low and the mic preamps are so hissy that I’d hesitate to use them even for telephony. (line-ins are great though)
  • They default to stereo mode every time they are plugged-in, so you need to open Apple’s Audio MIDI Setup Utility (AMS) to switch to 4, 6, or 8 channel modes.
  • They have an extra output jack that is not an independent output: it mirrors the 1/2 outputs. (It’s labeled “line out” on the Sabrent and has a headphone symbol on the Diamond).
  • All outputs comfortably drive a variety of headphones. If you can live without analog volume control then there’s no need for a headphone amp in most situations.
  • I tried connecting 2 interfaces simultaneously. They both showed up in AMS with the same name. I combined them into an aggregate device and selected it in Reaper, but playback stopped as soon as it started. It seems like it doesn’t work. I haven’t gotten any farther than that.
  • I haven’t tried S/PDIF digital IO, sorry.

Diamond XS71U details:

Diamond XS71U

Diamond XS71U

I heartily recommend this one. It is made of regular shiny plastic, not the Sabrent’s gross sticky smelly stuff, and the channels aren’t routed backwards like the Sabrent (always a plus!)

Mic Input:
It has 1 stereo mic jack with terrible sound quality.

Line Input:
The stereo line input sounds great.

Output Channel mapping: (according to the router in Reaper)

Channel Mode in
Audio MIDI Setup
Labels printed on 1/8″ jacks…
F-out SS-out BS-out C/B
2 Channel 1/2
4 Channel 1/2 3/4
6 Channel 1/2 5/6 3/4
8 Channel 1/2 7/8 5/6 3/4

 

Sabrent USB-SND8 details:

Sabrent USB-SND8

Sabrent USB-SND8

It smells like a dollar store! It’s got that rubberized matte plastic finish that will get sticky and gross after a few years. For me this is reason enough to avoid it.

Mic Input:
It has 2 mono mic jacks with terrible sound quality.  They are labeled backwards (Mic 2 is Left, Mic 1 is Right).

Line Input:
The stereo line input sounds great, but it’s also backwards. (Left and Right are swapped)

Output Channel mapping: (according to the router in Reaper)
** Note the backwards panning on the C/Sub jack! So much backwards stuff on this box!

 Channel Mode in
Audio MIDI Setup
Labels printed on 1/8″ jacks…
Front L/R Side L/R Rear L/R C/Sub
2 Channel  1/2
 4 Channel  1/2  3/4
 6 Channel  1/2 5/6 4/3
 8 Channel  1/2 7/8 5/6 4/3