I have a question regarding the iMac: could the processed audio be recorded on the MBP itself, or is a separate recording device vital? Is it because the output is also monitored? And since both the iMac and MBP seem to support S/PDIF, would a lossless digital audio connection between them be possible?
These are good questions.
In the current setup, the iMac handles the recording of audio for two reasons.
First is it’s less load, as the iMac, using Sound Studio (Audacity could also work here) is recording the Audio Hijack-processed “broadcast output”. That is: the Audio Hijack filtering stack I’ve set up on the MBP is what gives the output the sound of analogue broadcast radio.
Meanwhile, the DJing console, Algoriddim djay, is
also recording (with its built-in set-record feature) what I can the “raw” recording, pre-Hijack (like an in-studio recording at the source, typically for archival reasons). Having this “raw” source is handy in the rare case something needs to be re-sourced during post-production. I
could have the MBP handle two different recordings simultaneously, in addition to Hijack processing and also the djay front-end itself, and I think it would probably handle just fine. But this brings up the other reason…
…which is, I do want to actively monitor the broadcast output visually and in real time, to make sure I give the “broadcast” output adequate raw headroom so to stay well clear of clipping. Were this analogue, it would be less an issue, but digital, of course, is very unforgiving around clipping.
As for S/PDIF, this was actually the very first thing I tried, since it made sense to try that first.
Unfortunately, I ran into intractable problems with software-based/system-based routing: analogue audio RCA input ported from the Behringer midi controller’s audio output to the MBP (which is RCA analogue only, as I believe the dual, discrete sound cards inside the Behringer are wired solelyfor analogue audio output, via single RCA set) refused to re-route outbound as S/PDIF output. This was, when first setting it up, the problem against which I kept banging my head without finding a way around it.
I even tried using my 17-inch MBP, which also has two, discrete S/PDIF ports, as I ran djay from it. Of course, the audio input from the mixer is still analogue, which seemed to be a problem for OS X to then re-transmit that input as a digital, S/PDIF output stream. (The same, I found, when using the iMac directly to input analogue audio and to send digital optical signal to the S/PDIF input on my preamp, as the preamp and its monitors are
the montoring device for what the “broadcast” actually sounds like: it didn’t work.)
It seems the only way I’ve ever managed to get a Mac to output digital optical audio when is when: A) the digital audio being generated is on the device itself (e.g., running iTunes); or B) the input source from another device, to be routed as digital optical output, is
also digital optical audio. This digital-in/digital-out setup is, in fact, how I’ve configured my G5 in the past, with success.
But hybridizing analogue in/digital out? It seems OS X does not like that very much. Maybe there’s a workaround, but after nearly two days of troubleshooting, I finally settled on the analogue/copper wire audio setup, where the only digital involved was in the recording software itself. Ultimately, for this particular project (which, by design, invites imperfection!), this works out just fine.