measure delay time

Let’s assume a two-channel track was recorded with two microphones with a large distance between them (10m or more). Is it possible to mark a short piece in this sound track (for example one second), and then calculate a correlation between the two channels and measure the best-fit delay time?

Where was the sound source?


The sound source is a bird in a tree. I want to measure the delay time between two (or four) channels and then delay the cannels by exactly the correct amount and then add all channels, so that the signal is enhanced and noise is reduced.

There are some DSP devices coming to market that can do this kind of wizardry.

Have a look at the MiniDSP, fi:

It’s 95$, has 2 or 8 audio channels and the software to do beam forming and noise reduction. The board has 7 on-board MEMS mics and a connector for an eight channel.

I’ve been experimenting with these two for a while and doing it after the fact, without monitoring while you’re recording is a Very Big Problem.

To start, with, you need 4 channels and a very precise mic setup to make it work. Any small mistake and it doesn’t work.

You could do it for this mic setup, but it’s a lot of work. And the next setup is different, meaning you need to redo most of it.

I started with a parabolic mic pointed at the source and a wide cardio to the rear and the idea it would be a simple polarity/reverse and summing thing. It isn’t, because of the difference between the two mics and the phase issues.

It’s not completely useless, but requires a lot of work. And there’s a wealth of software out there for free that uses the Ambisonic 4 channel formats. Less work, but you need a suitable four channel setup.

Everybody tries the cancellation trick when they’re learning how to microphone. There is one variation that works and is recommended by Elecro-Voice.

You sticky-tape two matching microphones (EV, of course) in parallel so their two heads and two connectors are jammed together. You make up a special “Y” cable with one of the two microphones wired backwards. When you turn the system on, very nearly nothing happens—until you speak directly over one of the two microphones. Everything else cancels.

It’s not Boston Symphony, but you can use this technique to do a news piece in some insanely noisy environments.

Most other cancellation techniques fail.