Posts Tagged ‘Gear’

Portable Audio Recorders

May 10, 2010

For a few years now we have seen a wealth of portable audio recorders appear in the market. Most record two tracks at 96 kHz, 24 bit and have integrated stereo microphones.

While the 96 kHz, 24 bit suggests high quality audio recordings it is the integrated microphones that spoil it all.  Unfortunately not many manufacturers document the specs of the microphones on their devices. Even elementary information like whether the mics are cardioid or omni is often lacking. Instead we are left with descriptions like “Internal Stereo Microphone”. No noise performance indications or frequency response information. Clearly a sign most of these devices are not positioned as devices for the professional sound recordist.

Luckily a few websites come to our rescue. Of note here are www.wingfieldaudio.com who provide excellent noise floor samples and www.avisoft.com who provide both noise floor samples for a few models and EIN data for a fairly complete range of portable recorders available in the market today.

In my experience an Equivalent Input Noise number of -120dBu, unweighted and at maximum gain setting is the minimum for the field recordist to be able to make decent recordings. Also, a frequency response of 40Hz through 20kHz is a minimum specification to be met.

On the noise spec that rules out popular recorders such as the M-Audio Micro Track II and the Edirol R-09HR. These might prove effective in high dBFS music recording environments but are pretty useless to record in quiet environments.

Two recorders in my view perform particularly well: the Sony PCM-M10 and the Sony PCM-D1.

The PCM-M10 has very quiet omnidirectional built in microphones. Omnidirectional microphones are less sensitive to handling noise (nice to have on a handheld device) and have extended low frequency response.

The PCM-D1 has Analog Devices pre-amps that are virtually noiseless. The microphones are cardioids mounted in an XY coincident pattern. While this would suggest a narrow stereo field Sony managed somehow to overcome this and give recordings made this device a wide stereo image. Might be a device that is hard to find these days as it seems to have been discontinued in some countries in favor of the PCM-D50.

The microphones on both recorders are high sensitivity so dealing with quiet environments is no problem. The D1 has better high-end response compared to the M10.

Samples of recordings I made:

PCM-M10: JanuarySleet.wav, ThunderandRain.wav

PCM-D1: QuietForestSpringEvening.aif, LakeSide2.wav

Mid-Side recording and Microphone Sensitivity

November 1, 2009

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.

Recording the Umbrian Hills

July 24, 2008

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.

New gear

April 16, 2007

900hz rig

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