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I don't know if this question is related to DSP, but I'll give a chance.

Introduction: These days there are a Guitar Synthesizers which allow the guitarist to play another instruments like: brass, drums, strings, pianos and other guitar models from his guitar.

It possible to turn any guitar with the MIDI Pickup, that sends the all data that the synth needs. Now, from what I understand the pickup turns the guitar into MIDI one.

My question is how a signals like those that the guitar makes can be converted into MIDI instructions ?

There is a sampling before this conversion? I think that it should be, because if not. How the Synth will know in which level (volume) or duration to produce the sounds?

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  • $\begingroup$ I advise you to edit your question and remove the references to specific brands/models - what you really want to know is how guitar to MIDI interfaces work, right? $\endgroup$ – pichenettes Dec 12 '13 at 22:20
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There is a sensor for each string which individually records the string vibration. This signal is converted to digital, analyzed for estimating its fundamental frequency and its amplitude (envelope detector). Whenever a sharp increase in amplitude is detected, a MIDI note on message is sent, at the detected frequency. Whenever the amplitude falls below a threshold, a MIDI note off message is sent.

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  • $\begingroup$ I know that all the sounds are stored in the device memory. but they won't store each sounds in a different level of volume,right? I mean when the amplitude of the guitar's signal is low, the device will check if the amplitude is low but it won't search the stored sound with a low level of volume, right? It outputs the stored sound and with DSP changes his amplitude with the amplitude that related to the guitar's signal, right? $\endgroup$ – Elior Dec 12 '13 at 22:50
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    $\begingroup$ The MIDI pickup only outputs MIDI data, not sounds. It is up to a synthesizer/sound module to translate the MIDI messages into sounds. A large palette of synthesis techniques can be deployed there, but volume adjustment is commonly done by applying a gain on the signal (mostly in the digital domain nowadays). There are exceptions, thought - for example a sound module could use multi-sampling so that a different sample is played from ROM when the velocity exceeds a threshold. This is because striking a harder note on an instrument not only impacts amplitude, but also harmonic contents. $\endgroup$ – pichenettes Dec 12 '13 at 22:58
  • $\begingroup$ Thanks :) and just for a personal knowledge, the electronic drums have a module, so you can choose any type of drums and percusssions. those drums are connected to the module with a PL cables for each drum and cymble. So the module just have a recorded sounds of drums and when you drum on some drum, it produces the recorded sound right? the cables are just transfer a data about the hit level and which drum was hitted right? $\endgroup$ – Elior Dec 13 '13 at 8:58
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    $\begingroup$ The cables are just carrying the signal recorded by the force sensor in the drum pads (in the oldest electronic drums, they were just switches). The drum module processes these signals to detect hits and measure the impact strength, and this information is used to start the playback of a pre-recorded sound; or to initiate the generation of a synthetic sound. $\endgroup$ – pichenettes Dec 13 '13 at 9:24

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