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Arbitrary signal math with Perl functions
Variables available for your function:
$ch1 channel 1 input
$ch2 channel 2 input
$out output: '$out = ' is assumed before your function; don't use $out
@ch1 channel 1 "memory", $ch1[0] = previous sample, $ch1[1] = one before that
@ch2 channel 2 "memory", ... all the way to sample length
@out output "memory", $out[0] = previous function output calculation, ...
$t sample number, or "time", 0=left edge or trigger point
$pi a constant: 3.14159265359, for your trigonometric convenience
Example functions
Functions of channel 1 (would also work for channel 2):
abs($ch1) # rectify (absolute value)
-$ch1 # negate (invert)
$ch1 - $ch1[0] # integral or rate of change since last sample
$ch1 - $ch1[2] # same but over more time (3 sample periods)
$ch1 + 32 # add a "DC offset" of 32 sample units
$t > 43 ? $ch1[43] : 0 # delay by 1 msec @ 44000 S/s = 44th sample
Functions of both channel 1 and channel 2:
$ch1 * $ch2 # multiply 1 * 2
$ch1 / ($ch2 || 1) # divide 1 / 2, avoiding divide by 0 error
$ch2 / ($ch1 || 1) # divide 2 / 1
$ch1 > $ch2 ? $ch1 : $ch2 # max(1, 2)
$ch1 < $ch2 ? $ch1 : $ch2 # min(1, 2)
$ch1 + $ch2 # sum, like the oscope builtin
$ch1 - $ch2 # diff, like the oscope builtin
($ch1 + $ch2) / 2 # average, like the oscope builtin
Time position ($t) functions, independent of channel 1 and 2 inputs:
$t / 88 % 2 ? 64 : -64 # 250 Hz square wave (88 = 44000 / 2 / 250)
sin($t * $pi / 44) * 64 # 500 Hz sin wave (44 = 44000 / 2 / 500)
cos($t * $pi / 22) * 64 # 1000 Hz cosine wave (22 = 44000 / 2 / 1000)
Low-pass filter: a difference equation of previous input and output:
1.899105 * $out[0] - .901531 * $out[1] + .001213 * ($ch1 + $ch1[1] + 2 * $ch1[0])
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