Sunday, June 03, 2007

I'm inventing a music synthesizer!

For those of you who don't know, and for the further edification of those who do, I am applying for two patents in the field of music synthesis. The first patent is very general and relates to Digital Signal Processing (DSP). The second is probably more interesting from a musical point of view.

Highlights from the second patent:


An input analog signal is first digitized and then processed by a DSP whose clock frequency is an integer multiple of the fundamental frequency of the analog signal. The signal is then decomposed into its individual harmonic components. Each harmonic is subjected to a selected gain or attenuation, and then the modified harmonic components are summed to reconstitute an output signal with a different harmonic profile than that of the input. The final result is converted back to an analog signal with a D/A converter."

"It is expected that creative selection of a signal source, and of the values of the [gain coefficient]'s, will yield interesting results. For example, if the input source is a human voice, and the harmonics are modified to resemble those of a violin, the output signal will have the attack and decay, in other words, the dynamics and agility/versatility of the human voice, but the harmonic timbre of a violin. It is evident that this method can be applied to transform the sound of any instrument into any other, or actually into the sound of fictitious instruments that don’t actually exist in material form."

I am working on a prototype of the synthesizer which will allow it to be demonstrated in real-time. What happens next will depend on how much interest I can generate via demonstrations at trade shows, etc.

I am really excited, because I came up with this idea about ten years ago but I had no idea how to implement it. Thanks to working as an analog design engineer in the real world for eight years, I have finally solved all the implementation details.

My first prototype boards for my synthesizer arrived on Friday, June 2, and I assembled one board and verified that it works! This circuit is just the analog portion of the synth, and doesn't really convey what the full synth will do. I created two sound clips demonstrating what the circuit does. I recorded myself playing trombone (badly) to see whether the synth will be capable of processing the trombone sound. Here is the first clip:

The original, unaltered trombone is on the left channel and the synth output is on the right channel. Use your balance controls to alternate between the two channels so you can see what it's doing. Essentially, the synth is stripping out all of the harmonic content of the sound above the fundamental and converting the fundamental into a square wave. In order to do this, the circuit uses an adaptive tracking filter which self-adjusts its cutoff frequency until it passes only the fundamental. The circuit also has a test mode to disable this adaptive tracking filter. This second sound clip has the tracking filter disabled:

You can hear that in this clip, the synth output sounds "dirtier" than in the first clip. This is because the higher frequencies are passing through to the output. The synth in this test mode behaves more like a classical "distortion" effect, and while it might sound "interesting" at this early stage, this mode won't be useful in the final synth implementation.

The next step could take several months, but I will continue to work on it after I move to Europe -- in fact, I may have even more time to do it over there, so it could be completed earlier than expected!

The test board is shown in the photo. Now accepting pre-orders! Ha!