Notices by Don Romano (alt) (thor@noagendasocial.com), page 46

2) I'm guessing that what your typical ADC does is integrate the PDM signal until the next word clock edge comes along, at which point it places the sum in a shift register and begins to clock it out.

For an ADAT slave device with ADCs that output a PDM signal, I suppose what you need to do is similar. You'd use a PLL to derive your oversampling clock from the word clock, and integrate PDM bits until a word clock comes along.

1) Trying to figure out how professional audio interfaces expect ADAT Lightpipe data to be aligned relative to the BNC word clock output. Your typical ADC takes the word clock as a trigger to begin outputting the next PCM sample. Since you can't begin to output the bits of a PCM sample before you've demodulated the PDM signal from the delta-sigma modulator, this implies a one-sample delay.

@awg https://www.youtube.com/playlist?list=PLHoGZ7nuFTo8VmQBhzZxl-qDEIN7T5Vt8

This guy, a professional microphone designer, explains it well.

@awg I find that I can get surprisingly far with just high school math and drawing what I'm trying to understand, or attempting to visualise the system in motion in my head. I strongly dislike it when the solution to a problem I'm trying to solve is a matrix equation. To me, that's like a black box where you plug in the numbers, and out comes the answer, but you're not sure why...

@awg The polar patterns are actually one of those things you could work out in your head without any calculations. "Okay, so if the waves are coming head on, what is going to add up or cancel out if I imagine this in slow motion?"

@awg The way I deal with it is to look for verbal explanations. *Some* of the math is simple enough that a high schooler could understand it. Sometimes, you don't need the hard math to pull clever things off.

@awg I wish I understood it even better. I struggle with the math behind it.

@awg Well, it's not that hard to find this information. It's the sort of thing you'd find in a book on microphone techniques for professional recording.

@awg And I think you'd get a similar characteristic if you just space two omni mics apart, invert the signal from one, and sum the signals. And if you combine with another omni mic? Well, one side of the figure out will cancel out one side of the omni and you're left with sensitivty on one side only, and that's what a cardoid pattern is, so...

@awg You'd intuitively not expect a figure-eight microphone to vibrate at all since the sound reaches both sides of the diaphragm, but it works because the sound has to travel round the back and the time that takes gives the diaphragm time to move.

@awg 3D pickup pattern for a figure-eight microphone.

@awg

@awg Does this sound right?

@awg Now if you extend this and make an X-shaped array with 5 mics, that would also double as an X-Y pair. The center mic is still omnidirectional but now it does double duty as the omni element that turns the figure-eights crossing it into cardoids.

@awg I'm trying to work out what would be a good 3D arrangement of MEMS microphones to accomplish all the common polar patterns.

I think a figure-eight pattern would result by simply having two mics spaced apart, inverting one microphone and summing the result?

A cardoid pattern is just an omni plus a figure-eight, so I guess you'd just add a third omni microphone in the middle to get that.

I think this would also let you do nice M-S matrix stereo recordings.

@awg With MEMS microphones, they talk a lot about beamforming using arrays.

@awg There is one part of music production that hasn't been democratised: Production skills.

It's funny how many times I've been told the following: "Your stuff sounds great! What software did you use?"

People think the trick is to own the right stuff. What they don't get is how a parametric equaliser works, how you use the side channel on a compressor, what a middle-side matrix is, or how you EQ your channels to avoid a muddy mix.

@awg So anyway, I'm curious about what I could do with some MEMS capsules and a bit of DSP. Maybe I could have 8 of them in some kind of pattern and just convert to ADAT and then experiment with them in a DAW and write a plugin or something. Not sure yet.

@awg So anyway, I'm curious about what I could do with some MEMS capsules and a bit of DSP. Maybe I could have 8 of them in some kind of pattern and just convert to ADAT and then experiment with them in a DAW and write a plugin or something. Not sure yet.

@awg I get the impression that most music today isn't even recorded in a traditional studio. They might go there to lay down vocals, but even that is a bit showy if you ask me. The affordable Focusrite interface and budget large diaphragm microphone I have at my desk is more than capable of making a good recording. If I had world class talent in my living room, I'm sure I'd get very good results.