Limping back into life...

Doesn't look all that exciting but the Hellfire Modulator is slowly limping back to life. The old sticky panel has been peeled off -- quite a task! and the holes re-drilled for two of the pots with switches and the larger hole for the PWM range switch made smaller -- quite a task II! and now we are getting back to being able to where we should have been 3 years ago...

Asthetic has Knobs on....

This is a bit of an experiment in a number of ways. I have started on an 8 channel Envelope Generator that is based upon an enhanced DX7 style envelope control. I am also considering that really Forbin is going to be a bit big... I know that I am getting ancient and that large chicken head knobs are easy to see and that it all looks a bit Emerson circa 1974 but 40 years later I don't really have the space! Come what may the OctoEnvGen will be useful however it is packaged. It was a bit interesting to see though, how small a Euro synth actually is! I need to finds some knobs without markers on them though... These aren't pots but continuously rotating switches which control a TFT display which draws the waveform...

Cloudy

Well a bit more daydreaming and have been experimenting with a few ideas. I have always been fascinated by the MOTM 520 Cloud Generator VCO. It is a bit of an expensive beastie having an original price of $500 and no DIY option. That has become a bit easier with a DIY option for the E340 being offered but still $270 + postage and the $US Vs $AU is not in my favor at the moment... Anyway the aesthetic behind Forbin is not to spend much money, just to be unique and learn a bit so this represents my experiment with similar ideas. I have no real idea how they do it internally but I have prototyped up 4 sine wave oscillators with separate Brownian noise sources that modulate the 4 oscillators. The Brownian rate of change (well frequency I suppose -- Chaos Bandwidth in E340 parlance) and amount that it is tweaking each of the oscillators (Spread on E340) seem to all work fine. I want to make the number of oscillators also continuously variable rather than just stepped. I also need to do some thinking about a soft clipping arrangement Vs a an amplitude compression technique. I plan to rework this in Assembler after some of the prototype parts in C have been bashed out. The nice thing about the CortexM4F is that there are truckloads of floating point registers -- actually 32! so it is possible to leave a lot of the parameters in the CPU rather than loading them in and out of memory all the time... The sample frequency of this thing should be around ~150kHz to 200kHz so hopefully not too many artifacts will get through. It is pretty impressive what you can get out of a $7.99 evaluation board + a simple DAC!

Wavolver ii+

Made a PCB for Ian Fritz's Wavolver II but have made the Pulse Mix and the Fold Mix voltage controlled as well. I am now contemplating an 8 channel Envelope Generator to allow me to control all these elements at once... Haven't quite got it all going yet but certainly en'route to success...

VS Voice

A bit more prodding and pummeling and for a bit of a laugh I loaded up a sample from the Sequential Circuits VS Synthesizer. This is allegedly waveform #20 from the wavetable. I have no idea if it is correct or not but there is an interesting interview with one of the chaps, Chris Mayer, that helped designed the VS and he mentioned that he wanted the interpolated sound of a short samples. Worked out that I can get all of the factory waveforms of the VS into one 48pin QFP... Thinking maybe a 7 segment display and a digital pot to choose the waveforms. Could do the joystick thing... could also do two control voltages for up/down and left/right. Might just start out with two waveform selections and a digital mix and see how we go from there...

sin(sin(x))

Well into a little bit of DX VCO... The DAC works, the FPU works, the SPI works, some fairly basic code works and we end up with this! Did cheat a little and end up using a lookup table rather than a Taylor series. Since I really don't need the resolution and when you start scratching the surface the Taylor Series is a reasonable amount more mucking around than it appears and to try and run this as fast as possible I pinched some table generation stuff that I used for the LFO a while ago and re-jigged it a little bit. This is about 400Hz and the sample rate is up around 176kHz with a 16 bit resolution. Now need to get the ADC going...

The spider...

Oh well... What could Possibly go wrong now?
Actually looks like it might work...

Small...

Hmmm... this is the 16 bit DAC that I bought... it is hiding in the shadow of the Evaluation board and as you can see from the 0.1" spacing of the standard DIL pitch are going to make this a challenging bit of work to wire it up... hopefully more successful than earlier in the week...

Cortex M4

New project! yep another one... Looking at building a Digital VCO, there are a couple of options here; Texas Instruments, Atmel & STMicroelectronics. I am also getting a different TI part that has the the Cortex M4F core which has floating point! Pros & Cons? Well the Atmel board has 1Mbyte of external RAM, which will be really good for my wavetable VCO. The ST chip can boot along at 168MHz. The TI one I am probably the most familiar with... There are other options out there as well, the Frescale parts (was Motorola) have a more accurate ADC but it is still really only about 14 bits really (the trouble with having sensitive analog parts on a digital substrate), the NXP parts are also quite neat in that they can come with multiple cores so one core can be monitoring the ADC values whilst the main core can be doing the calculations... What I hope to end up with is a couple of different VCO's. The wavetable one that gets the samples from an SD Card. A DX Voice one that uses FM and looks like a single voice of my DX7 but the frequency is 1V/octave. A harmonic oscillator that looks a bit like a cross between a Farlight Page 5 and a Buchla 148 Harmonic Oscillator, well at least Mark Verbos's take on it here. I would also like to do another Buchla favorite, the 259, with the whole gamut of dual modulation of phase, frequency, amplitude and timbre... All I need is a little more time...