A Bit of Tech Talk, Part 2

Technology II:  To continue the story, the microphones deliver a signal to the mixer, more importantly, the mixer’s pre-amplifiers.  Nature recording in the desert presents a tough challenge to sound equipment, because the recorded signal is almost never loud enough.  Those few subjects that produce a loud song, or call, or howl are typically far enough away that their volume is quite low by the time the sound reaches the microphones.  This requires equipment that can amplify a low level signal without generating too much internal self-noise that gets mixed into the intended signal.  When amplifying a low level signal, inferior equipment will produce excessive self-noise, which can be heard as “hiss” when the track is played afterwards.  For my mixer/pre-amp, I find the Sound Devices Mix-pre D, 2-channel mixer to be a solid piece of equipment and a good value.  It has adequate levels of gain and exceptionally quiet pre-amps.

One of the unique features of the Sound Devices mixer is its ability to export a 2-channel AES digital signal.  I take advantage of this feature and connect my SD mixer to a Marantz PMD-661 digital recorder.  The Marantz is one of the few handheld recorders that makes provisions for a digital “input” connection.  Marantz utilizes the S/PIDF format, a consumer format which is still compatible with the AES professional format.  I installed a Canare AES impedance matching transformer between the mixer and the recorder to insure compatibility.  Even though the Marantz has its own built-in pre-amps and XLR microphone inputs, the Sound Devices electronics are superior by an order of magnitude.  This relegates the Marantz to operate simply as a “bit-bucket”, a final destination where the digital signal is recorded onto an SD flash drive.  The Marantz will record the signal in a couple of different formats, and I choose to record in the uncompressed WAV format and set the sampling rate at 48KHz and the bit-depth at 24 bit.  This yields a clean, noiseless file with the integrity to withstand the creation of multiple copies for the purposes of editing and distribution without degradation.

During the last few years digital technology has revolutionized nature recording by allowing small, durable (and affordable) devices to record hours of high-quality sound.  By the previously mentioned settings, I can record about four hours onto a 4-gigabyte SD card.  Gordon Hempton, a leader in the nature recording business, used to define a quiet location by whether it was free of human or mechanical noise for at least 15 continuous minutes during daylight hours.  It sounds simple, but these locations are much more rare than you may realize.  In those days, Mr. Hempton recorded on a Nagra reel-to-reel field recorder.  “Nags” were used extensively in the movie industry and where considered to be the “gold standard” of portable analog recorders.  Each reel of tape on a Nagra allowed for the continuous recoding of … 15 minutes.  So if there was no human or mechanical noise recorded on the entire 15 minute reel of tape, he deemed that location to be very quiet.  By the way, many of Mr. Hempton’s recordings are available on iTunes.  For my money, his tracks are the “gold standard” for nature recording.

Blog Post #8 2 Blog Post #8 1

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