plgDavid discovers glitches in NES triangle

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tepples
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plgDavid discovers glitches in NES triangle

Post by tepples » Tue Dec 10, 2019 9:19 am

In the FamiTracker users' Discord server, it was reported that plgDavid took a 100 MHz scope to the TND audio output pin of a 2A03 playing a high-frequency ($400A=$400B=#$00) triangle wave and discovered glitches on the rising portion of each wave, halfway up and all the way up.
plgDavid_triangle_glitches.png
My guess: The XNOR gate changes the state of the output sent to the DAC before the carry has had a chance to fully ripple through the counter.

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dougeff
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Re: plgDavid discovers glitches in NES triangle

Post by dougeff » Tue Dec 10, 2019 12:19 pm

Question.

This is the signal directly from the 2a03, right?

Would the TV speakers transmit this error? Speakers are mechanical. They have to move from point A to point B and back.

Perhaps, you wouldn't be able to hear the error, like it would be mostly smoothed out, due to the very short time it drops and goes back.
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lidnariq
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Re: plgDavid discovers glitches in NES triangle

Post by lidnariq » Tue Dec 10, 2019 12:31 pm

At most, there'll be some faint impulse train sound mixed in with the stairstep distortion. In practice, I bet the glitch is on the order of 30ns long (maybe shorter) and would be too quiet to be audible.

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Bregalad
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Re: plgDavid discovers glitches in NES triangle

Post by Bregalad » Wed Dec 11, 2019 12:32 am

dougeff wrote:
Tue Dec 10, 2019 12:19 pm
Question.

This is the signal directly from the 2a03, right?

Would the TV speakers transmit this error? Speakers are mechanical. They have to move from point A to point B and back.

Perhaps, you wouldn't be able to hear the error, like it would be mostly smoothed out, due to the very short time it drops and goes back.
If this is really with $400A=$00 $400B=$00 then you wouldn't even be able to hear the signal which would already be ultrasonic.

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