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Registered Member #1143
Joined: Sun Nov 25 2007, 04:55PM
Location: Vilnius, Lithuania
Posts: 721
Hello, since i need ability to play any song on my DRSSTC, i decided to make universal MIDI controller. Idea: open song with Labview, convert it to spectrum , and use maximum energy frequency for PWM frequency. So PWM frequency will be calculated based on frequency, and compare register value (or duty cycle) will be based on power of that frequency.
I already developed FT2232D to SPI interface, that can send small packets at 5-7KHz repetition rate, so no wories here
Sounds good ? Well, no, this approach works on well defined single tone song parts, but is complete mess for normal songs. Any one have ideas, or maybe want to help develop it ? if some one helps, i will make 3 copies of this interrupter, and i can fully assemble it prior shipping to you.
Tomorrow i will make video to show how it works, and maybe you can help to make it better. Also it will be easy to mix two or more PWM signals to generate polytone interrupter signal, for even better result !
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
The flaw in this idea is that if you send, say, 400Hz to the coil, it produces 400Hz plus all of its harmonics. The harmonics are very loud and can't be got rid of, so if the original music signal didn't contain them, you are screwed.
Some sort of cepstrum approach might help to identify harmonic series in the original music signal and choose a few fundamental break rates that would reconstruct them. This might reduce the distortion somewhat but it's never going to make a DRSSTC sound like a flute.
An alternative approach is to treat each DRSSTC bang as a delta function, then the sampling theorem says you can reconstruct an arbitrary signal from a train of them. But this requires an extremely high break rate, as the break rate is the sampling rate. Good luck making a DRSSTC that can run at 44100 bps.
My personal solution is to plug an electric guitar into it. The distortion introduced by the DRSSTC is quite similar to a fuzz box so it looks like I did it on purpose. I had plans to process each string separately, but I'm told that this makes the guitar sound like an accordion. The heavy intermodulation between the strings is actually a vital part of the rock and metal guitar sound.
Registered Member #1143
Joined: Sun Nov 25 2007, 04:55PM
Location: Vilnius, Lithuania
Posts: 721
I am facing few problems. If song only has one nice sharp tone, interrupter does reproduce that right. Problem arise as you stated from harmonics, since low frequency for humans will create less impression, and harmonics will have distortion that will degrade sound dramatically, but also one of main problems is that main beat or sound that will be asociated with that song does not always sit in highest power frequency
In other words, we care more in shades than in colors.
Second problem is even if i can send data from labview at 5-10kHz with all information for PWM circuit, song is played by chunks, and i get speed reduction down to 500Hz repetition rate...
This interrupter is only good if song is played in background, at this point humans will associate song sound with Tesla coil
But hey, is only few hours of real work ( well, more, but that only because i am still new with labview, and extracting data from clusters, arrays take some time)
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Music driver for DRSSTC based on labview and STM32F4
