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The Theremin has two very high frequency oscillators (around 350 kHz). One of them is fixed, and the other is varied by the capacitance of your hand: it's the difference between the two frequencies which decides the pitch.
29 Δεκ 2004 · Then when you mix the 500 kHz to 505 kHz oscillator with a fixed 500 kHz one, you would end up with an audiosignal of 0 to 5 kHz. This doesn’t only allows us to play music, but has another advantage: its possible to make an instrument with a range of 3-5 octaves.
Depending on your hand position and the adjustment of the instrument, the beat frequency can be anywhere from around 65 Hz to about 3 kHz (260 kHz minus 257 kHz). These are audio frequencies, and they correspond to a range that spans from about two octaves below middle C to about three-and-a-half octaves above middle C.
Calibrating the Frequency Signal The frequency range for the Theremin should be at least two octaves (220 to 880 Hz). A second LabVIEW subVI called Scale Frequency.vi, as shown in Fig. 5, converts the second photometer signal level into a frequency level. The photometer input (0 to 6 V) is converted into an audio
4 Σεπ 2009 · With pure sine waves it's simple - if the input frequencies are 175kHz and 176kHz then the difference is 1kHz (audible) and the sum is 351kHz - well above the audible range and in the RF range. With other waveforms you have to consider the harmonics as well as the fundamental frequencies.
The mid ranged frequencies, between 5 kHz and 15 kHz, are filtered into the bandpass filter and are responsible for the mid-tone of the signal, and the frequencies above 15 kHz are filtered through the highpass filter and are the treble of the signal.
The resulting signal is a single frequency (plus harmonics) in the audio range. The frequency of the volume oscillator is used to control how much the audio signal is amplified. As you move your hand, the frequency changes, so the amplifier's gain changes, and thus the output volume changes.
