Digital Ins and Outs

The miniDSP 2x4 kit, miniDigi and cheap Chinese Hifiberry Digi+ knock-off have arrived. Hurray! Let's see if any of this works...

The first thing is to get the Digi+ SPDIF/Toslink interface going on an RPi. I happen to have a spare one (of course!), so I've cloned the SD card from one that works, popped the Digi+ hat on top, and wound it up. Oops - no sign of the Digi+ in the MPD config menu... So time for a quick SSH onto the RPi, vi /boot/config.txt, edit the dtoverlay param so that it includes the hifiberry_digiplus, and now it's recognised. Hurray. You might think the smart money would be on trying something known to work first, like my Focusrite Firewire audio interface with SPDIF out, but hey.

miniDSP 4-way Advanced application

Now for the miniDigi and 2x4. The miniDSP documentation is a bit dodgy, and needs careful reading. I rigged up the miniDigi and 2x4 using the provided 30-way headers, connectors and ribbon cables - there are two sets of connections, only one of which is documented much. This is the I2S interface, I assume the other is about power connections and so on. Time to select 1) input - Toslink initially because they gave me a cable! 2) output - looks like it's ok. I powered it all up from the Mac USB connection, and cranked up the 4-way Advanced configuration application. Bleuch - nothing!

Check the manual - oops, need to ensure I2S Master and Slave relationships set correctly. Set miniDigi to Master. Now there's sound, but a horrendous crackling that drowns out music, and it's constant. 

Check the manual again - check 2x4 MCLK master/slave setting, which is currently Master. Poo - should be Slave (this is not intuitive, but hey... what use is intuition in these matters?). Switch to slave, re-stack boards. Hurray!! Sound, clean, no noise, expected selection of Left/Right on 4-way Advanced interface.

RPi SPDIF i'face, stacked miniDigi/2x4

miniDigi (top) and 2x4 stacked (SD card over bright blue LED!)

Summary

1. RTFM properly!
2. miniDigi - I2S Slave
3. 2x4 - MCLK in Slave position (I2S signals coming from miniDigi)

See what I mean about it being non-intuitive? I guess the difference is between MCLK - the signalling rate indicator, and I2S Slave - who's boss on the interface.

Next Step

Make up the custom connectors, since the provided ones only allow for a single 2x4 to be connected to a miniDigi. More on this to come...