David Kronemyer

Mixing SPDIF Modules and Samplers to Logic 8

March 10th, 2009 by David Kronemyer · 5 Comments

DAVID KRONEMYER: Over the years the studio where I produce many records has accumulated a variety of MIDI sound modules (“ROMplers,” so called because their sounds typically are stored on a single ROM chip) and samplers. The MIDI sound modules include older ones made by Roland, E-Mu, Yamaha and Alesis, together with others. The newer ones are made by Access Virus, Nord, Novation, Waldorf and others. The samplers are Akai, Kurzweil, E-Mu and Roland. At one point this studio probably had 200 sound modules and samplers in a dozen floor-to-ceiling racks. All of them were/are MIDI-controlled and stereo out.

The last generation of sound modules made right before the advent of VST instruments have SPDIF digital outs. These are intriguing because they suggest the possibility of by-passing a stage of digital-to-analog (“DA”) conversion before introjecting the sound into ProTools or Logic. Most digital converters (such as the Apogee Ensemble and all of the other Apogee converters) have a SPDIF digital in. The problem is there is only one of them, which creates a challenge to mix all of these separate digital sources.

Surprisingly there are not a lot of SPDIF digital mixers. Almost every mixer now made claims to be a “digital mixer” and they are in the sense that they take analog signals, mix them and then convert them to SPDIF or AES-EBU digital. None of them however mix signals in the digital domain, which is what one might think a “digital mixer” does. After exhaustive research we concluded that the best (and possibly the only) solution to mixing actual digital signals is the Roland M-1000. It accepts four (stereo) SPDIF ins and also a (stereo) analog input.

We took 24 modules and connected them to six M-1000s as depicted in the accompanying photo (one M-1000 not shown). We established a limit of 24 modules for this exercise because we devised a way to address each of them separately in Logic (which will be the subject of a separate post). The problem with this set-up was that the Ensemble (like all other Apogee converters) only has one SPDIF in. Thus it was only possible for one M-1000 at a time to address Logic. The other ones had to go through a DA conversion phase out of the M-1000 and then another analog-to-digital (“AD”) conversion phase through the Ensemble. Although these were high-quality conversions it still basically defeated the purpose of remaining exclusively in the digital domain.

m-1000-mixer-system

We experimented with ganging four M-1000s into one M-1000 as a kind of digital summing mixer however this lead to audible jitter and other undesirable digital artifacts. To stay exclusively digital we ended up disconnecting and reconnecting M-1000s so as to address that elusive but desirable single SPDIF port.

After a while we decided that this system was a lot of trouble. So we decided to utilize the on-board DA converters on each of the modules and mix straight into Rane SM82 mixers. These are analog but then went straight into the AD conversion phase of the Ensemble. The results are depicted at the second photo. We also retained one M-1000 so we could continue to use the Ensemble’s sole SPDIF port. The Ranes are stackable and in principle we could have tripled the inputs for this revised system. We retained the 24 module limit however for further interface with Logic’s MIDI control system.

sm82-mixer-system

We were not able to discern any sonic difference between this set-up and the initial one using the M-1000s. We also were able to stay with a single AD-DA conversion cycle. From this we concluded that the DA converters on the last generation of ROMplers and samplers are as good as (or at least indistinguishable from) their respective SPDIF outs through a digital mixer and then into Logic through Apogee converters.

A post on addressing 24 MIDI channels in Logic simultaneously will follow shortly.