Nectarine
Infamous OneLiner
Agemixer
(02:40:20)
wire that result back to some PC or C64 port's input line, so that can notice when this input is toggled, then this triangle signal sample sent to the port is the actual sample value reached the same value 
OPAMP just does the comparison
Agemixer
(02:35:11)
the output of this opamp gives the result, at "exactly at time" the value rised higher compared to o reference signal, giving out 0;or 5volts, "0" or "1" bit.
Agemixer
(02:32:24)
add a simple OPAMP chip to your card board. Give the (+) pin the audio input signal and the "(-)" pin this reference signal.
Agemixer
(02:29:34)
a very simple ADC converter: you can make this DAC, then manually drive it a triangle waveform, starting from 0 and adding up to value 15, fast. this gives a reference signal.
Agemixer
(02:27:04)
so that 0000 gives out 0 volts, 1000 (=8) gives out 2,5 volts and 1111 (=15) gives out that almost 5 volts.
Agemixer
(02:25:13)
simplest DAC (audio out) a set of resistors, into user port or such... in a way that each bit does halve the DC offset of the output signal.
Agemixer
(02:22:33)
or, straight out from I/O. Like... disk drive or cassette 1-bit line 
Agemixer
(02:21:22)
Rap and you also asked where to get that sample data from. My dump answer is.... basically, from memory address onwards (using indexer or not, to advance to next sample;anyway)
Agemixer
(02:05:49)
probably some other better ideas, but that's one "easy" approach to explain.
Agemixer
(02:04:51)
lda sample,x , sta SIDsampl, inx, nop*6, lda sample,x , sta SIDsampl , bit $dcod .... or something, double writes during badline. Probably a scanline table lookup to check whether a badline occurs there.