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Zelenka Music Press
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Signal ProcessingThis page is about signal processing on a nylon-string guitar using piezo pickups.There are only three pickup technologies. (1) Microphone - senses vibrations in the air. (2) Magnetic - only works on steel strings. (3) Piezo - senses mechanical vibrations in the wooden top. Only the third of these is appropriate for nylon strings. Although the combination of microphone and piezo pickup is used by many players, I don't use this. A raw piezo pickup has a horrible sound and requires considerable electronic signal processing to be usable. I misunderstood this for many years: I didn't want any "signal processing" because I wanted a "natural sound". Unfortunately the piezo pickup is not a natural sound, because it takes vibrations from the wood, not from the air. It produces an entirely different sound profile than does a microphone. This sound profile must be "processed" into a more acceptable and "natural" sound. A microphone, if it is of good quality, theoretically requires no signal processing - it is indeed the "natural sound", and good quality mics do give an acceptably "natural" sound. But this is possible only in a pristine sound environment, and a commercial musician does not have that luxury. A microphone picks up and amplifies everything in the room, and in a crowded restaurant this creates feedback so that the crowd noise increases - people can't hear themselves and so they talk louder - and the signal-to-noise ratio gets pretty bad. We (Jack and Frances) used microphones for about two years, and then switched back to piezos. The piezo pickup's response has a huge spike at the beginning and tapers off rapidly, whereas what we want to hear is a smooth attack and a long sustain. Also, the piezo material itself, a ceramic, puts out a signal at 2 million ohms of impedance, and until this frequency is stepped down, it is not compatible with standard sound equipment. The piezo pickup requires several stages of processing: (1) step down the impedance (2) "equalize" the frequencies to sweeten the sound (3) compress the signal to eliminate the spike and increase the sustain (4) add "reverb" to imitate the echo of a natural sound in a room. Information on all of this will be posted here... soon... or someday! |
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More Information to be posted...! |
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