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change approach, too much m4

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Wolfgang Hottgenroth
2018-05-08 17:25:41 +02:00
parent 10e888649b
commit 54a933c83a
87 changed files with 256 additions and 2081 deletions
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23
posts/2013-07-01.01/article.html
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@ -1,15 +1,6 @@
<html>
<head>
<title>Projects - just for fun</title>
</head>
<body>
define(`TITLE', `Theremin')
define(`DATE', `2013-07-01')
define(`CONTENT', `
<p>
A <a href="https://en.wikipedia.org/wiki/Theremin" target="_blank" rel="noopener">Theremin</a> is a rather old electronic music instrument, invented in 1928. It is played by approaching hands to two antennas, without touching them. One antenna is used to manipulate the frequeny of the tone, the other one to manipulate the volume.
</p>
@ -57,7 +48,7 @@ This term can be modified using the addition rule for trigonometric functions in
<p>
Due to this transformation, two signals, one with the sum and one with the difference of both input signal frequencies, are accumulated.
When both frequencies are exactly the same, one part of the sum appears as a DC offset, while the other part is the doubled frequency.
If one oscillator is de-tuned by only a few Hzs, one part are this few Hzs (a very low, hearable frequency) and the other part is still (roughly) the doubled frequency (a high frequency). The high frequency part can now be suppressed using a lowpass-filter.
If one oscillator is de-tuned by only a few Hz'`s, one part are this few Hz'`s (a very low, hearable frequency) and the other part is still (roughly) the doubled frequency (a high frequency). The high frequency part can now be suppressed using a lowpass-filter.
Multiplication of two signals can be done using an analog four quadrant multiplier, like the AD633. So, this is the schematic of the mixer+filter block:
</p>
@ -132,8 +123,4 @@ The output signal of this block in turn is the volume-controlled and frequency-c
<p>
<a href="https://www.youtube.com/watch?v=lDld71HI66o&amp;w=420&amp;h=315">Playing the Theremin</a>
</p>
</body>
</html>
')