From the chat room tonight, Warren reports:
<Warren_O> some mostly good news to report...
<Warren_O> the boosted file still didn't work, even though it measured 0.220-0.230V... but... if I run the audio through a cassette deck to boost the level, it works great
<Warren_O> I think the measured voltage level is greatly affected by frequencies like the 60 Hz static in analog LD audio, so it isn't giving me an accurate representation
<Warren_O> so I've at least determined that it *is* possible to get a low audio error rate with dexter
<Warren_O> we just need to do some more testing and adjusting to get it right
<Warren_O> I need to make sure I'm getting as much output from the Pi as possible (right now it's using an old raspbian image from CAX, in which the mixer doesn't seem to work right)
<Warren_O> and then need to filter/eq/maximize the mach3 audio to get it as close to original as possible
<Warren_O> if that's not enough, we may need an op-amp stage to boost the level
<Warren_O> but I will worry about that later if it becomes necessary
What he is saying is that the Raspberry Pi seems to be outputting too weak of an audio signal (by itself) for MACH 3's hardware to pick up the target data on the audio channel. There are 3 things we can do to fix this: a) increase the audio to maximum level inside the laserdisc image file itself (he already tried this), b) crank the Pi's audio output to its maximum strength (we don't yet know if we have any mixer that the pi offers cranked up), c) add an audio amplifier to the Dexter board to force the audio to the correct level.
We will prefer to avoid 'c' if we can help it since it will add to the cost and complexity of the board. But we'll do it if that's what it takes. The good news is he verified that with the correct audio level, MACH 3 can read the target data properly which is a huge win for MACH 3 owners everywhere :)
Warren also tested with the VBI Injector board to see if MACH 3 could pick up the frame numbers. Unfortunately, I had a bug in the latest firmware which caused the "white flag" to always be drawn and it turns out that MACH 3's hardware relies on the white flag _never_ being drawn. I've done a quickie fix but can't test it from my present location.
All in all, things are looking very promising.