Mic processing & On-air processing


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Periodically, it's good to review the current state of audio processing technology. The manufacturers that we are all familiar with, and some that are new to the business, are rapidly meeting our needs with respect to data-reduced (or simply low bit rate) transmission pathways. In addition to those changes in functionality there are more and more examples of updated input and output protocols.

There is nothing new about the technique of adding separate audio processors for studio microphones. What started off as a way to give jocks a bit of boost in certain characteristics of their voices (most notably low frequency equalization) has evolved slowly over the years and now includes not only EQ, but also compression, gating and downward expansion. Other changes in broadcast technology are reflected in modern microphone processors as well, such as the addition of digital outputs and word-clock inputs.

Aphex has recently introduced the 230, the latest in its long line of mic preamp/processor boxes. This is a single channel, 1RU device that has a vacuum tube (12AT7) mic preamp, parametric EQ, compression, gating, de-essing, +4dBu and -10dBV analog outputs, along with digital outputs (AES, S/PDIF and optical formats) with 24-bit resolution (96kHz sample rate).

Mic processors have evolved into highly configurable devices, such as the Aphex 230, the dual-channel Air Tools 6200, or the Yellowtec VIP/Digital with built-in card reader.

Airtools by Symetrix offers the 6200 digital voice processor. This is a two-channel, 1RU device containing two processing chains that will work at mic or line level, in a stereo mode or independently. Standard processing features, such as high-pass and low-pass filters, compressor/limiter, four-band parametric EQ and downward expansion are included. Processing settings are configured from the front panel or from 6200 Designer, a Windows application. After the unit has been programmed, real-time control of the device is available by PC via RS-232, USB or Ethernet. Symetrix also offers the 528E.

TC Electronic manufactures the Gold Channel, a 1RU, two-channel mic preamp and audio processor. The mic preamp in this unit is immediately followed by an A/D converter, which allows for all processing functions, such as compression, expansion, equalization and de-essing to be done in the digital domain. The user can save settings in any one of 100 memory locations, and the unit comes with 100 factory presets as well. Aside from balanced analog outputs, there are digital outputs (AES, S/PDIF and optical (TOS-link) formats).

Focusrite offers the VMPRO channel strip, a 2RU single channel mic preamp and processor. This unit boasts a (solid state) class-A mic pre, along with the following processor sections available on the front panel: expander; vintage harmonics; compressor; tube sound; and voice-optimized EQ. Analog outputs are standard, digital outputs are optional.

DBX has been in the processing business for years and has recently manufactured the 376 (with digital outputs). This 1RU mic preamp/processor begins with a vacuum tube microphone preamp followed by a (semi-parametric) EQ, compressor and de-esser. The digital output has selectable sample rates (44.1-, 48-, 88.2- or 96kHz) and adjustable word length (16-, 20- or 24-bit) in the AES or S/PDIF formats. Word clock input and output is via BNC connectors.

Aircorp offers the 500PH, which is a single channel, 1RU mic preamp and processor with three channels of graphic EQ; phase rotation; compression and expansion; an insert point; de-essing; mic and line level outs, and a headphone out that allows the engineer to set up the unit without having it actually on air.

Yellowtec manufactures the VIP/Digital, a 1RU device that stores its settings to Smartcards so each user can establish his own presets. It includes mic and line inputs, analog and AES3 inputs, 24-bit A/D-D/A converters, 100 internal presets, an FFT-based de-esser and reverb.



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