Setting up multichannel soundcard

I’m trying to use a multichannel soundcard but no matter what I try only the first two channels seem to be usable.

In the boot process I can see the soundcard getting selected and all channels seem recognised:

Booting server ‘localhost’ on address
Number of Devices: 13
0 : “Built-in Microph”
1 : “Built-in Input”
2 : “Built-in Output”
3 : “Scarlett 18i20 USB”
4 : “BlackHole 16ch”
5 : “Microsoft Teams Audio”
6 : “Screenflick Loopback”
7 : “Loopback Audio 2”
8 : “Loopback Audio 3”
9 : “Surround 5.1”
10 : “Quad enhet 2”
11 : “Quad M4&404”
12 : “M4 - 2”

“Scarlett 18i20 USB” Input Device
Streams: 1
0 channels 20

“Scarlett 18i20 USB” Output Device
Streams: 1
0 channels 20

But when opening the meter only two channels show up. And trying to send audio to channel 3 or 4 doesn’t work. Giving the command Server.default.options.device_(“Scarlett 18i20 USB”); before of after booting the server doesn’t make any difference.

The sound card channel 1-4 do work from Reaper.

I’m on MacOS 10.13.6/iMac 2011.
I’ve tried my other Mac min M1/MacOS 12.4 and soundcard MOTU M4 but get exactly the same - only 2 channels show up in the meter window.
SuperCollider 3.13 used on both computers.

run this before booting the server:


Or 4 or 6 or 56 or whatever number of outputs you have

Place that line of code in your startup.scd file (edit it by going to File->open startup file) and then restart SC. Then you will have 8 channel output forever without having to worry.


Thank you very much - you made my day!