AUTOTUNE for everyone

[analogmonster]

Hello everyone,

some keyboard synthesizers like the Memorymoog and some Oberheim synths offer an autotune feature for their (analogue) oscillators. This allows the instrument to tune itself. A certain keyboard or note range is scanned and compared with internal frequency tables to determine a set of control voltage offsets which are used to compensate environmental temperature changes and other reasons for changes in tune or scale.
AFAIK no separate external or module based circuit for modular analogue synthesizers exists up to now to be post-installed as a circuit extension or separate module. Especially the older analogue modulars like the Moog System 55, 35, 15, IIP, IIIP and their reissues have to be retuned due to instrument warm-up, circuit age, environmental changes etc. which can be an annoying process as it is a repetitive and iterative process. But this can happen to each and every analogue VCO.

I ran into this problem with my 901ABBB VCO bank clone of my Moog System 55 project, as I cloned it close to the original, especially the exponentiator with all its problems. So I asked myself whether it is possible to gain digital control over the oscillator if you want to play tonal to automatically compensate all those drift effects due to warm-up, age, etc.

So I decided to develop an AUTOTUNE module as stand-alone device to be added to a modular synthesizer as a separate module to take over control over analogue oscillators, to keep them in tune and / or scale automatically without permanent effort of manual re-tuning or re-scaling. AUTOTUNE for everyone, not only for some players of some special keyboards.

Basically it is a kind of control and feedback loop, or better to say a kind of regulator circuit. It is able to send and receive MIDI sequences as well as sending and receiving control voltages.

Please find a description of the human interface and an integration example for modulars below.

Youtube: T908 Demo

More information on the module web site.

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T908_Kit.jpg
Description:	Special offer: Board and programmed microcontroller Euro 50.00 - Please contact me offlist via carsten@analog-monster.de if interested
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T908_Integration.jpg
Description:	T908 integration example:
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T908_Front.jpg
Description:	The T908:
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[analogmonster]

New firmware version 1.06 for the T908 AUTOTUNE released. The module provides two additional program functions now:

"P4": SAVE EEPROM: The control voltage offset list which is currently in use can be saved in the module permanent storage EEPROM.

"P5": LOAD EEPROM: The control voltage offset list to be used can be loaded from the module permanent storage EEPROM.

With these functions another AUTOTUNE FULL run after a module RESET or POWER DOWN can be avoided.

Complete list of module functions up to now:

1.) "P1": AUTOTUNE Full Run:
That's what you see in the demo. 5 Octaves (c0 - c5) are scanned and compared to the internal frequency table, a CV offset is derived from the deviation and stored in a program-internal note list.

2.) "P2": AUTOTUNE Online:
Auto correction is done during your play, and each note you play is rescanned and checked again, the CV offset list is adapted and the correction is corrected In this mode the warm-up phase of an analogue VCO like the 901 or your studio door suddenly being opened by your little daughter who wants to tell you that she ate two pieces of cheese cake does not have to be compensated by doing another full run.

3.) "P3": AUTOTUNE Offline:
Auto correction is done during your play according to the CV offset list of the full run. No rescan is performed. Needed for e.g. usage of PORTAMENTO. This is the way the Memorymoog and some Oberheim synths work, AFAIK.

4.) "P4": SAVE EEPROM:
As described above

5.) "P5": LOAD EEPROM:
As described above

[analogmonster]

New firmware version 1.08 for the T908 AUTOTUNE released. I use all 12 bit of the DAC now. Now you can (theoretically) catch VCOs which are +/- 2.5 octaves out of tune and out of scale - but this is rather academic, I'd say. No VCO is that much out of tune and out of scale in a modular environment. But the question is: How far can I go with it.