Small technical backgrounder this time.

When recording stereo it is essential to have equal gain settings for the microphones at the risk of the stereo image shifting to either left or right. More gain on the right mic channel will shift the image to the right and the other way around. Equal gain settings are especially important in XY, ORTF or any other spaced or coincident microphone positioning.

With mid-side recording the gain setting for the mid and side channels allow you control the stereo spread. More gain on the side channel compared to mid will widen the stereo image. More gain on the mid channel will narrow the image. Ultimately, no gain on the side channel will leave you with a centered mono signal from the mid mic.

Reading gain or trim pot settings is easy enough but you usually end up with differences in signal strength if you don’t take into account microphone sensitivity even with an equal gain setting on your recorder or mixer. Unless you have a matched pair, microphones have different sensitivity characteristics.

A typical MS setup is the Sennheiser MKH60/ MKH30 microphone pair.

The MKH60 has a sensitivity of 40mV/Pa, the MKH30 has 25mV/Pa. With equal gain you will end up with a much stronger mid signal and consequently a narrow stereo image.

The calculation to compensate for sensitivity is as follows:

±dB = 20 x log(MmV/SmV)

where

MmV = sensitivity of the mid mic in mV/Pa
SmV = sensitivity of the side mic in mV/Pa

In our example we need 4.1dB more gain on the side channel compared to the mid channel to get equal signal strength on both of the recorded channels.

This is easy to realize on mixers such as the Sound Devices 302. With MS stereo linking set trim pots allow you to set gain for the mid and side channels separately. The input 2 fader controls the overall gain for the pair.

Going to Italy next month travelling through Tuscany and then setting up near the small town of Gubbio. I was there last year. So being more familiar with the surroundings should make things easier. 

Being mobile and travelling light is not exactly compatible with trying to make as high as possible quality recordings. The stereo rig will be a Sennheiser mid-side setup but I also plan to do as much hydrophone recordings as possible. Part of the trip will be following the River Arno upstream out of Florence. Let’s see how that goes.  Pelican cases to the rescue.

Gear:

Sennheiser MKH 60
Sennheiser MKH 30
DPA 4060
Aquarian Audio H2a-XLR hydrophone
Sound Devices 302 field mixer
Nagra ARES-PII+ recorder

The DPA’s will find their place in Chris Watson’s tried and tested sonic coathanger setup. One of the things I learned when we were with him last December.

The Nagra continues to amaze me. No other recorder delivers such high quality in so small a package. You can put it in the inside pocket of your jacket. 2-track only but such great preamps, phantom power and 24 bit resolution.

Finally got the Sound Devices 302 field mixer. Got some interesting new recordings done with it. Expect uploads of the sounds soon.