Tag Archives: audio engineering

Surround recording techniques: Double M/S and IRT Cross

17 Jan

As part of the tasks to complete for our Digital Studio Production module at the Master in Audio Production in Salford University, we were asked to do two surround location recordings with portable equipment if possible. These recordings would be later mixed into 5.1 Surround format in the studios as part of our assessment… and it’s also good fun too!

The first recording I did in this fashion was not properly “on location” but in our University’s recording studios instead, using their equipment in full. It all happened before the Christmas break, when some of us Master fellows joined there to make a “jam session” (some noise with instruments  such as guitars, bongos, a battered drumset) and record the resulting soundscape. The goal was to set ourselves as far in the corners of the live room as possible so as to create a wide soundscape to recreate via surround recording techniques.

My setup of choice for this surround recording was the Double M/S technique. But not the usual one with two Mid microphones and one Side microphone for both of them, all sharing the same space in place. Instead of that, I decided to use Curt Wittig’s techniquue, shown in ‘Spatial Audio’ book by Francis Rumsey. In this one, two separated MS pairs of mics are used: one of them will give the front signal and the other one will record the rear signal.  According to Mr. Wittig, the rear MS pair should be placed back in the room at a distance from the front pair further than the room’s Critical Distance (DC).

Double MS Diagram

Double MS setup diagram (taken from “Spatial Audio” by Francis Rumsey)

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Compromises in audio (I): Microphones

3 Nov

Since I started my engineering degree, I started to acknowledge (assuming it was way harder) that everything in life is a compromise between a great solution with a high cost and a “just OK” solution that’s much more convenient. Or as his Satanic Majesties The Rolling Stones very wisely said: “You can’t always get what you want/ but if you try, sometimes/ you get what you need“. Pop lyrics are sometimes more than great. Try to express it better and simpler, Yeats!

As I was saying before digressing, there is no perfect solution that covers all of the issues that we might face with no drawbacks at any point. The audio and acoustic world is one of the best exponents of compromises being made to achieve the best possible solution, which is far from perfect but is the best we can get with the technology or knowledge that we have at the present moment.

If we start by the first link in the chain from acoustic source to storage medium, we have the transducer, this is, microphones. And microphones are one of the biggest examples of a compromise solution if we have a look at them. Let’s take the difference between condenser and dynamic mics to start with. Simply put:

  • Condenser mics: Good (fast) time response able to capture accurately transients due to the diaphragm’s low mass, which means great high frequency response… they directivity might be switchable from omnidirectional to cardoid or figure of 8. The drawback? They’re mechanically very delicate and they need a constant voltage between the diaphragm and its backplate (48 V Phantom power or prepolarized electret).

A condenser microphone (Photo by Bill Selak, under CC BY-ND 2.0)

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