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"The Sequential Circuits Six-Trak was released in 1984 at a list price of $1295. It is 28’’ wide, 11 ¾’ deep, 4 ¼ high, weighing in at 18 pounds. It features a 4 octave, non touch sensitive, keyboard with non spring loaded pitch and modulation wheels located on the left hand side above the keyboard. My initial impression of the wheel location was negative but after using the board for about a week, I become accustomed to reaching above the keyboard for the wheels. The pitch wheel’s range is a third and is not adjustable. I prefer a spring loaded pitch wheel but this made up in the fact that the six-trak will send and receive pitch and modulation wheel data via midi. The six-trak is a six voice, multi-timbred unit that features an 800 note sequencer, arpegiator, and 100 patch locations. The back panel features and a single audio out (six would have been great and was later implemented in SCI’s multi-trak), midi in and out ports (where’s the thru?), and a control foot switch which can be used to scroll through programs and advance the arpegiator one step at a time.
Multi-Tambral/Keybord modes/Sequencer/Apregiator
The unit can be used in number of keyboard modes which will alter how the voices are assigned. When powered up, the unit is a six voice, homophonic synthesizer. You can program the patch to operate in unison mode which will play all six voice at once (lowest note priority), or normal which assigns one voice to each key press. Triggering may be single or multiple. What is amazing is something SCI calls stack mode, which allows you to assign six separate patches (SIX separate timbres) to one key. When in stack mode you can turn off voices by simply setting their the ‘trak’ volume to zero for the particular voice. The unit can remember two of these stacks in the units memory. Additionally using its internal sequencer, you can assign six separate monophonic voices to each of the one six sequencer tracks. And you can play along with the sequencer using as many of the remaining voices that aren’t being used by the sequence. Once a sequence is recorded you can go back and change the applicable sequence’s patch and volume.
The unit offers a simple arpegiator which only uses the sixth voice. It can be assigned to play in an up/down mode or in the order the notes are played. The arepgiator may be latched and the remaining five voices may be used to play on top of the arpegiator. Unfortunately to get the unit to realize you want to change the arpegiation you have to take it out of the latch mode. Additionally the sequencer can not be used at the same time as the arepgiator - Probably to much work for the central processor.
The six track has an 800 note sequencer that is divided into two banks. Its a bit on the slim slide and I really don’t use it much. Once a sequence is recorded you can speed up or slow down the sequence from its initial recording speed. You can change the patch it will use to play the sequence but you can insert patch changes in the middle of the sequence. By turning the sequencer’s speed knob all the way to the left, the sequencer will sync to incoming midi clock. (Note: The arpegiator will not sync to incoming midi clock - this should have been implemented in the o/s ver .11 (final release) but wasn’t)
The VoiceEach voice is contained on a single CEM 3394 chip which includes a single VCO, VCA, and VCF. The LFO and three envelopes per voice are software generated. The VCO offers saw, triange, vairable pulse width waveforms, and more than one waveform may be selected at a time. The pulse width may be controlled by the LFO. The VCO may be modulated by its own dedicated ADSR which may be inverted and portmento (glide) is included at the patch level (much better than global i.e. Roland JX8P). The LFO offers either a square or triangle waveforms and can modulate the filter, VCA, and the pulse width. However the amount applied to each of these destinations is set using one LFO parameter and you can only choice if you want this amount to affect each of the three destination. There is no delay for the LFO either. The filter is great it can sound real dirty or pretty clean. The filter offers the cutoff, resonance (self oscillating), three levels of keyboard tracking (on, half, off), LFO on/off, and a dedicated ADSR which may be inverted. Additionally the filter may modulated by the oscillator’s triangle wave which is excellent and offers some really cool sounding effects. Last but not least the filter offers a mixer to mix the level of the oscillator and a dedicated noise source. The VCA has its owned dedicated ADSR and the VCA output level is programmable. Included at the patch level is a parameter to select normal or unison mode (see above).
Editing is done by using a 10 digit (0-9) numeric key pad to dial up the applicable parameter you wish to adjust. Parameter values are adjusted by a single knob. For some reason the evelopes only offer a range of 15 values for each parameter which is to restrictive for my liking. Almost all other parameters offer plenty of values. The two digit LED will display the patch number, or the parameter number or parameter value. Clearly knobs for each parameter would have been great but would have increased costs. This method is reasonably simple and easy to get used to especially once you become familiar with parameter numbers which is listed on the front of the synth for easy reference. The only draw back is that you can't see what parameter you are editing and its value at the same time. On the Multi-trak, Sequential devised a grid for selecting paramters which is quite good.
So how does it sound? Let me first say that is no OBXa or Memory Moog when it comes to obesity and lushness. Having said that though, I still think it sounds great. Its sounds analog and it excels at making synth sounds. While a second osc would have been nice - it was obviously not included to keep the cost down and not to directly compete with the Prophet 600. However having the ability to modulate the filter with the oscillator and having three separate envelopes in tremendous. And the ability to layer six different sounds on one key will provide you with massive fatness at the expense of polyphony.
MIDIThe six trak has a midi in and out ports but no thru port. The unit may operate in onmi, poly, or mono mode. In mono mode each monophonic voice is assigned a midi channel so the unit can be used in a multi-tambral fashion via a midi. It would have been nice if the unit used a voice allocation scheme (preferably dynamic allocation scheme) so you could have played more than one voice on each channel if there were unused voices.-but I dont think any manufacturer had implemented this feature back in 1984. The unit can perform system exclusive dumps of its sequences, stacks, 100 programs, or single programs. The unit will send and receive program changes, pitch and modulation wheel movements. Additionally the unit will respond to parameter changes but not send them. (Does anyone know if the ability to send them was implemented on later operating systems). Local on/off is also provided which allows you to turn off the six trak’s keyboard. The best midi feature of the six track is that each paramter will respond to a specific midi continious controller number (cc#). Paramter 0 will respond to message sent by cc #2, parameter 1 will respond to messages sent by cc#3 and so. Essentially, just add 2 to the parameter # and you have identified the CC# that affects the parameter. One word of caution, the cpu of the six trak is not that fast and if send the unit more than 4 or 5 of these cc commands at one the unit will lock up. However for most practical uses it works fine and realy lets you control the unit via midi."
. If anyone knows if it's any good feel free to comment. The following is the description on Amazon. I also added it to my 
