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semi virtual sax

A real mouthpiece connected to a virtual instrument body
  [vote for,

Digital musical instruments tend to be very limited in expressiveness compared to real physical ones. This is because only a few control signals are used, like key on/off, as opposed to the continuum of ways that a musician can interact with a real instrument - like guitars, violins, brass. On the other hand acoustic instrument design is very much limited by practical issues that don't exist in the digital world. I propose a new kind of instrument where the main resonating body itself is composed of real and virtual parts.

Imagine a saxophone where most of the body is cut off and replaced with a system of electroacoustic transducers (microphones and actuators), such that it behaves identically to a real saxophone body. This should be possible in theory because that behavior can be described as a linear time-invariant (LTI) system, which is almost trivial to implement in DSP.

There are a few big problems to solve. In the following, "incoming" means from the mouthpiece towards the end, and "outgoing" the opposite.

1.) The natural reflection from the end of the tube must be eliminated so that it can be replaced with a virtual reflection.

2.) Any pressure or velocity signal measured along the length of the tube is a mixture of both incoming and outgoing waves. These must be separated, as only the incoming wave should be fed to the DSP. Otherwise the system would just self-oscillate.

3.) The incoming wave has a significant "DC component". Air is not simply vibrating, but there's the more or less steady flow. This must be let through without too much resistance.

There's an alternative way to simulate the body, which might be easier to make but sounds dubious in theory. Instead of creating a "virtual" reflection wave, just pick up the incoming one, and feed the outgoing signal directly to the reed via some setup of magnets. The reed itself could be ferromagnetic, and a strong solenoid with a permanent magnet core needs to be embedded in the mouthpiece. At the very least this should create a controllable feedback loop, but I'm worried that mouth resonances which are important in playing especially high notes and bends might not work if the reflected wave isn't fed into the player's mouth through the mouthpiece.

orbik, Jun 12 2016


       Hmm. It sounds simpler to simulate the saxophone using a saxophone.
MaxwellBuchanan, Jun 12 2016

       // linear time-invariant (LTI) system // Not really, the elasticity of the air around the horn is quite non-linear (or so I've been told).   

       If your goal is only to produce an electric sax, why not go analog rather than DSP? I have quite an interest in electric wind instruments, and I've found that sampling the signals (and certainly trying to squeeze it through MIDI) is never good enough to feel right. For this you'd need to sample the air pressure, velocity, reed pressure and position all at greater than 44kHz, which is a lot of data. And then the DSP needs to run with sufficiently low latency to be unnoticable, even two or three milliseconds can make it feel disjointed.
mitxela, Jun 12 2016

       Ohhhh, *sax*. Sorry, it's getting late. Never mind me.
zen_tom, Jun 12 2016

       That reminds me, I’ve got a Yamaha VL70m I no longer use and really should sell. That was a superb physical modelling synth when I used to use it.
Ian Tindale, Jun 12 2016

       Six years between postings [orbik].   

       Welcome back.   

       The idea is to make a real physical instrument, not a synthesizer, just that it could be partially controlled and tuned like one. When the sound is generated by an actual reed and mouthpiece, the player can directly and naturally play overtones, bends, growls, multiphonics...   

       The main differences to a real sax would be having unlimited pitch range, customizable response (strength, phase, harmonicity), electronic key switches, and of course being a lot more quiet.   

       Oh and isn't the non-linearity of air mainly relevant at the narrow end where pressure amplitude is greatest?
orbik, Jun 17 2016


       // Digital musical instruments tend to be very limited in expressiveness compared to real physical ones. //   

notexactly, Jul 14 2016


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