adventures in DIY music

Saturday, 13 May 2017

Akai AX-60/S612 synth/sampler combo

I wasn't initially very excited when an Akai S612 sampler was bundled in with a second-hand deal I was doing. A whole one second of sampling time at 32kHz - woo hoo!! And then I read in the manual about the multi-voice output and it's use with the Akai synths of the day, and got curious.
When I finally found an AX-60 (they were rare even back then in the early 1990's) to partner up with it, I discovered the way these two units work together over midi and the proprietary voice interface was quirky and unique.

As a midi synth of it’s time (1986) the AX-60 had a pretty limited spec - no sys-ex, no velocity or aftertouch, response to CC#s 1 , 7 , and 64 only, and pitch bend. Yes, it had an arpeggiator, but this didn’t clock to midi, it required an old-fashioned voltage trigger for external sync. However, there was a big plus. It was bi-timbral, with a programmable split point, and separate (adjacent) midi channels for each timbre. You could allocate voices either side of the split in several defined ways. You could save the whole set-up - split/voice allocation/patch numbers/midi channels/unison and chorus settings - to one of eight “SPLIT PRESETS” for instant recall.

But it was when you hooked up midi, and the 13 pin DIN cable, to the Akai sampler that things got really interesting.
The multi-way connector allows the 6 voices of the sampler to enter the 6 voice channels of the synth individually. Hitting the “SAMPLER” button on the synth then does two things: it sends a midi mode change message CC# 126 to the sampler, putting it in midi mono mode, and it likewise puts the synth into (a kind of) mono mode. Now, note values generated by the synth CPU will be allocated to one of the six voice channels, and that note will be transmitted on a midi channel 1 to 6, that corresponds to the voice number. Thus, when a synth note is generated on midi ch. 1, Voice 1 on the sampler is triggered and sent to the synth’s voice channel 1 to be affected by the VCF, VCA and chorus circuits. This works for the arpeggiator as well - in fact, this is the only way to get the arpeggiator to transmit its notes from the midi out. (That last fact in itself gives you some interesting options when interfacing other synths with the AX.)

So what happens to this combo when you apply some of the other features?

In Unison mode, it works as expected, pressing a key generates 6 notes on 6 midi channels to the sampler to be processed by the synth. With chorus on, this can be quite a thick sound, but perhaps you wouldn't call it lush.
In Unison + Arpeggio mode, again as you would expect, each arpeggio note is transmitted in 6 note unison.
In Split mode (so says the manual), you can't use the sampler interface. Er... except you can! Although the S612 is not bi-timbral like the AX (it can only hold one sample in memory), the sampler voices each side of the split are treated according to the separate patch settings for the filter, EGs and chorus, so it's kinda bi-timbral in this scenario. The special split voice allocation settings where there are 6 voices one side and zero voices on the other (so the "zero" side of the split can control an external unit) will not work here, because bizarrely there is no midi transmission from that half of the keyboard until you switch the Sampler button off.
In Split+Unison+Arp modes combined, things can get a little hard to keep track of. In the 2/4  voice allocations, you can have Unison on one or both sides, and Arpeggio on just one, and the samples will follow along.

All in all, a powerful and fun combination. So, of course, you would like to control this duo and their interactions from your sequencer, wouldn't you? Well, there is another quirk of the AX-60 that will mess this up if you're not aware. When the Sampler mode is engaged, the AX transmits the mode change to mono mode, but in itself, it only becomes a transmitter in mono mode, not a receiver! It will receive external midi commands, but only on the channels designated while it was in Poly mode. Even more bizarrely, it transmits only notes in mono mode, not pitch bend or mod wheel. Those CCs get transmitted on the Poly channel (or both channels if in Split mode). Phew! 
But hang on, the S612 responds to both pitch bend and mod wheel in mono mode, doesn't it?... in fact, it seems to respond to those CCs on any channel between 1 and 6. 
So, reliable sequencer control of the combo is going to require some thought. I'll grapple with this topic in a future post.

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