cr1901 changed the topic of ##yamahasynths to: Channel dedicated to questions and discussion of Yamaha FM Synthesizer internals and corresponding REing. Discussion of synthesis methods similar to the Yamaha line of chips, Sound Blasters + clones, PCM chips like RF5C68, and CD theory of operation are also on-topic. Channel logs: https://libera.irclog.whitequark.org/~h~yamahasynths
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<andlabs>
it's more a legacy option
<andlabs>
SysEx is fully supported here
<andlabs>
I assume the filter circuitry is responsible for decoding the 0s and 1s there?
<qu1j0t3>
andlabs: No, the output of the comparator would be
<qu1j0t3>
andlabs: the filtering presumably just removes HF noise (i'm not looking at the schematic)
<qu1j0t3>
andlabs: if this is the same circuit we looked at the other day, the comparator (op amp) is effectively a single bit ADC (thresholds iirc at 2.5v)
<andlabs>
oh we were talking about a specific part of that schematic
<andlabs>
yes that's just a bigger verison of what i linked a while ago and already misplaced
<andlabs>
I was calling this whole thing a "filter"
<andlabs>
if the network of resistors and capacitors before the opamp are a filter that have no bearing on what is considered a 1 or a 0 then ok
<andlabs>
okay so +5>(470 + 2.2K) / 2.7K>0 - I assume that thing connected to the + terminal of the op-amp at / is what determines the bounds
<andlabs>
and that just happens to be 2.5V since both sides would be equivalent
<andlabs>
unless the connection to the output line being after the 470ohm is significant
<andlabs>
but wait, why would KCS be based on a comparator
<andlabs>
and would that be 2.5V of 5V scaled to +0.0 in [-1.0 ... 1.0] for sample value or do I need to do some RMS stuff
<andlabs>
hmm
<qu1j0t3>
andlabs: an op amp configured as a comparator will hit one rail or the other
<qu1j0t3>
andlabs: and yes, it only cares whether the threshold is met or not
<qu1j0t3>
andlabs: (and some hysteresis if that's set up, which i think from our last conversation, it is)
<andlabs>
which helped clear some thing up I must have misunderstood last time
<andlabs>
I assume the 15k resistor that's between the reference and the output line is the hysteresis?
<qu1j0t3>
yeah that sounds correct
<qu1j0t3>
you can work out the actual effect of the hysteresis from op amp theory
<qu1j0t3>
it does affect the parameters of the conversion
<andlabs>
so beta would be 2.5 / (2.5*15) (with the kΩ canceling out)
<andlabs>
*2.5+15
<andlabs>
2*that*Vcc which is 5V is ... 1.43 V or so
<andlabs>
I guess???
<andlabs>
actually I should instead look at the two trip points
<andlabs>
-0.71V and +0.71V
<andlabs>
yeah I don't know what ot do with that info
<andlabs>
if I take beta and double it then I get 0.38 which I *think* was used in the MAME source for some drivers as the copmaarison of the raw sample value?
<andlabs>
(there has to be a better way to leanr this =P)
<andlabs>
also if it turns out this is doing the actual tape data decoding in software I'll be very surprised
<andlabs>
but I guess it can afford to do that since it's just voice banks
<andlabs>
no point in doing sysnthesis while the voices are changed
<cr1901>
I first watch this vid over 11 years ago and it still holds up
<cr1901>
I think it would be fun to teach electronics, but it really is NOT amenable to IRC :(
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<andlabs>
OK
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<andlabs>
and looking at casettes birefly again actually does MAME not support cassette interfaces that *don't* use remote control
<fseidel>
cr1901: thank you for that tangent, TIL: "[The Schmitt Trigger] was a direct result of Schmitt's study of the neural impulse propagation in squid nerves."