Trying to figure out how the below code works. Everything is straight forward. The code works as I ran it in qbasic in dos emulator.

But for the life of me I cannot figure out wth cap1 and cap2 are. I debugged the code and saw values being set, but I cannot figure out where the data is coming from. I assume it is somehow related to the function declarations. Been 20 years since I did anything with qbasic. Maybe some other old fogie can tell me what is going on here:

DECLARE FUNCTION integrate (sample, cap, tc)
DECLARE FUNCTION differentiate (sample, cap, tc)
COMMON SHARED accumulator
CONST pi = 3.14159
SCREEN 9: CLS

FOR timeConstant = 10 TO 600 STEP 100
accumulator = 0

FOR a = 0 TO 22 STEP .01
wave = 0
FOR h = 1 TO 10
wave = wave + SIN(a * h) / h
NEXT h

lopass = integrate(wave, cap1, timeConstant)

IF wave > lopass THEN
trigger = 1
ELSE
trigger = 0
END IF

hipass = differentiate(trigger, cap2, 20)

PSET (a * 30, 50 - wave * 20), 15
PSET (a * 30, 50 - lopass * 20), 14
PSET (a * 30, 100 + timeConstant / 4 - trigger * 15), 2
PSET (a * 30, 270 - hipass * 20), 15

NEXT a
NEXT timeConstant

END

FUNCTION differentiate (sample, accumulator, tc) STATIC
fsample = tc
leakage = 1 - EXP(-2 * pi * 1 / fsample)
capAvg = leakage * accumulator
accumulator = accumulator - capAvg + sample
differentiate = sample - capAvg
END FUNCTION

FUNCTION integrate (sample, accumulator, tc) STATIC
fsample = tc
leakage = 1 - EXP(-2 * pi * 1 / fsample)
capAvg = leakage * accumulator
accumulator = accumulator - capAvg + sample
integrate = capAvg
END FUNCTION

The output looks like the image.