by Steve Cunningham
The current crop of high-end voice processors are mostly analog units that combine a microphone preamp, a compressor, some EQ, and perhaps a de-esser. But when Danish audio manufacturer TC Electronic decided to design a voice processor, they took a completely different approach. After all, TC is known for their hardware Digital Signal Processing products, and for software plug-ins that mimic their hardware products. All of these perform their magic using ones and zeros, so why not build a voice processor that also uses ones and zeros? The result is the Gold Channel Digitally Enhanced Mic Preamp.
The Gold Channel is a single space rack unit that combines two independent, high-end solid-state analog mic preamplifiers with a wide variety of digital processing blocks, including expanders, compressors, equalizers, gates, and more. The DSP blocks, many of which are from TC’s other award-winning products, are fully programmable and take full advantage of TC Electronic’s expertise in coding for digital audio applications.
The mic preamps come complete with pads, phantom power, and lots of other goodies. Each preamp directly feeds a 24-bit A/D converter, and all audio processing is digital from there on. The A/D converters in turn feed a chain of up to four processing blocks each. You can insert DSP functions into the chain in whatever order you wish, and the functions can be different per channel. There’s lots of flexibility here.
The unit’s analog input and output converters are all 24-bit as are its internal data paths, and it has I/O connections for just about any digital format you could want, including AES/EBU, S/PDIF (on either RCA or optical TOS link connectors), and ADAT Light Pipe.
The Gold Channel’s internal clock nominally runs at 44.1 and 48 kHz, but it will handle digital audio with sampling rates up to 96 kHz via the digital inputs with a couple of restrictions. When working with 88.2 kHz or 96 kHz digital audio, you can have either one processing block on each channel, or three processing blocks on channel one only, and digital word clock must come from the external source.
THE FRONT PANEL
The front panel is attractive but busy. Each of the two channels is served by a gain knob and a collection of buttons that control phantom power, phase, mute, pad, and other traditional preamp parameters. There are also four buttons per channel for switching in the various kinds of processing, and a nice horizontal fourteen-segment LED meter with clip indicator that can monitor either the input or the output.
Almost every button has one or more green LEDs associated with it, so it’s easy to tell at a glance what’s turned on. However, the buttons themselves and the legends are small, and those of us with less-than-perfect vision have to get close to see all the options.
But there are many options offered here, including pads at values of 20, 40, and 60 dB, low cut filters at 60, 80, and 120 Hz, and a digital “Softlimiter” that appears between the input selector and the low cut filter. This really is a “soft” limiter that appears to kick in at about -4 on the input meter, and in use its effect is transparent.
The right side of the Gold Channel has the black-on-green backlit LCD display, FUNCTION select buttons, and the large PARAMETER and VALUE knobs. These comprise the main programming interface for the Gold Channel. The four dedicated FUNCTION buttons to the right of the display let you work with and edit programs, set the master input and output levels, and set user preferences. Each of these pages has an onscreen menu bar with options you can select using the left and right MENU buttons.
GOZINTAS AND GOZOUTAS
Starting from the right side, the Gold Channel’s rear panel contains the mains power switch and IEC socket for the built-in auto sensing power supply, two channels of balanced analog input and output on XLRs, an optical input and output for either ADAT or S/PDIF digital audio, and an RCA connector for word clock input. The manual incorrectly identifies this word clock connector as a BNC, which is a more standard connector for word clock, although it works just fine with the RCA connector.
Digital audio is also serviced by two XLRs and two RCAs for AES/EBU and S/PDIF in and out respectively. Next to these are MIDI In, Out, and Thru connectors, and a 1/4" jack labeled External Control In. This jack accommodates TC’s Master Fader product, and is used to control the Master Output Level.
The Gold Channel takes best advantage of all these connectors by allowing you to configure unused ins and outs as an insert. If your microphones are connected to the analog inputs, and the analog line outputs are feeding your console, then you can use the S/PDIF or AES/EBU connectors to patch your digital reverb into the preamp. Or you can bounce ADAT tracks through the Gold Channel using the Light Pipe interface, and use the analog ins and outs to insert an analog compressor. When using the Light Pipe, you can specify which two ADAT channels will be processed through the Gold Channel.
GETTING AROUND
The ample LCD screen uses a clever combination of text and graphical elements to illustrate the various functions. Furthermore, the screen responds to your commands. For example, if you grab the gain knob for channel one and turn it, the display automatically switches to the SETUP-GAIN page and shows you the dB value of that knob. Let go of the
knob, and in a few seconds the screen goes back to its previous display. You can prevent the display from switching back via a User Preference.
Each of the four PROCESSING buttons associated with the preamp channels has an LED that lets you quickly see what processors are turned on in a given program and channel. Pressing a lit PROCESSING button bypasses that particular processing block. For example it’s very easy to kill the EQ in a program — you just click the button to bypass the EQ.
The Gold Channel also features some very clever shortcuts for navigating to the editing pages. Double-clicking a PROCESSING button makes the LCD screen change to give you access to that processor’s parameters on the edit page. So to edit the EQ you simply double-click the EQ PROCESSING button, and the screen immediately shows you the EQ controls, ready to be tweaked.
The EDIT FUNCTION button reveals a set of screens that let you insert the processor blocks into the audio stream. This is where things get interesting. Using the LAYOUT and ROUTING menus, you decide what processing blocks you wish to insert and in what order. There’s a great deal of flexibility here, and you could conceivably have eight different DSP functions work on a single audio stream by feeding the output of channel one’s audio into the channel two audio stream.
You can store up to 200 of your own programs in a battery-backed User Bank in the Gold Channel, which is in addition to the 100 factory programs stored in permanent ROM. Any or all of your programming masterpieces can be write-protected to prevent the morning guy from trashing them, and you can transfer them to a PCMCIA memory card and take them with you for safekeeping. In any event, it’s important to save your settings regularly in the Gold Channel. There are a lot of things to adjust on this box, and you won’t want to have to recreate programs from scratch.
THE PROCESSOR BLOCKS
There are four categories of processing in the Gold Channel — Expander/Gates, Compressors, Equalizers, and a category they call Tools.
Expander/Gates come in two flavors: the Easy Gate and the Advanced Expander. They are essentially the same processor with different controls. The Easy Gate’s controls are threshold, maximum damping (or attenuation) and mode, which is either fast or slow. No other parameters are available in the Easy Gate. The Advanced Expander has all controls available, including ratio, attack and release times, knee mode, and hold time. It also adds a bandpass filter and sidechain monitor. For cleaning up general background noise, you’ll find the Easy Gate sufficient.
There are two types of Compressors in the Gold Channel that perform in two different ways. The Soft Compressor is a typical design that compresses the signal based on the threshold setting and on the level of the input signal. The Vintage Compressor has a fixed threshold, and you adjust the Input Drive control to make the compression kick in. The result is that the Vintage Compressor is smoother than the Soft Compressor, but the Soft Compressor has more control and is capable of delivering more extreme levels of compression.
Like the Expander/Gates, there are two flavors of EQ in the Gold Channel. The Easy Equalizer is a simple five band EQ with low cut, low shelving, mid peak, high shelving and high cut bands. Gain of the low and high cut filters tops out at +/-12 dB, and the others at +/-18 dB. The Advanced Equalizer is a five band affair with low bell/shelving filters, high
bell/shelving filters, and three fully parametric filters, all with a gain of +/-18 dB. For those of you who like to tweeze your sound with EQ, the Advanced EQ has the juice to do it.
The Gold Channel’s Tools category features a number of processor blocks that just don’t fit elsewhere. Foremost among these is a proper De-Esser with a bit of a twist. The threshold is referenced to the average signal level, so the amount of de-essing stays relatively constant even when the material gets louder. Next is a Dynamic Equalizer, which is basically a de-esser with more parameters and an enlarged frequency range.
Then there is a block that TC calls a Digital Radiance Generator. This particular widget adds a bit of second order harmonic distortion to the signal. The result sounds like slightly overdriven tubes or tape saturation, and in small doses is very pleasant. It’s a little compressed and sparkly. Controls for drive (amount) and curve (tonality) are included.
Finally there’s an RIAA Playback filter for processing the direct output of a turntable and — get this — you can choose between the IEC standard from 1964 or the standard from 1987 that includes a subsonic filter! The code jockeys at TC certainly did their homework on the Gold Channel.
GOLD CHANNEL IN USE
The first assignment for the Gold Channel was to substitute it for my existing tube mic preamp. I connected a Lawson L-47MP microphone to one of the analog inputs and connected an analog output to the line input on the console. I bypassed all the processing blocks, as I wanted to hear just the mic preamp. I then read and recorded several scripts in different styles, from soft narrative to aggressive hard-sell.
The Gold Channel’s preamp is a clean accurate circuit that delivered the signal from the microphone with a minimum of coloration, and with a good frequency response. It has the character one expects from a high-quality solid-state mic preamp, which is to say very little character of its own.
Adding the Softlimiter in the preamp section did indeed squash the loudest parts a bit, but did so very gently. It’s a well-behaved limiter that does its job without being audible.
From there I began to play with the factory presets. It is clear that the folks at TC had music production in mind when they developed their presets for the Gold Channel. The first two-thirds of the one hundred factory presets have names like “Clean Guitar Fender Amp” and “Bass Amp 4X10.” But many of the other presets are named after microphones, and one supposes they’re designed for those in particular.
I recalled the “U-87 Vintage Compressor” preset and recorded the same scripts using the Lawson. This preset uses the Vintage Compressor with a fairly high 8 to 1 compression ratio, and adds a gentle EQ boost around 3 kHz and cuts everything below 80 Hz. The resulting sound had more edge, and was a bit too squashed for my taste. Lowering the compression ratio to 4 to 1 gave better results.
The unit includes some presets that are extreme — and the Gold Channel is definitely capable of creating some extreme effects. In particular, the “Voice Tweezer” preset is an effect that I found downright unpleasant. I think they were going for a telephone sound, but the result was far too bright and harsh for my taste. No matter, with a bit of EQ tweaking I fixed it right up and stored it to a user preset.
On the other hand, “Lead Vocal Chain” is an example of a complex processor configuration that sounds very good. In this preset, the output of the channel one chain is fed into channel two and processed still further. It employs a total of five processor blocks, and the resulting sound is crisp and in-your-face without being harsh.
There are also factory presets for an AKG 414 and a Shure SM-7, so I put those mics up and recorded the scripts again. Each preset worked well with its intended microphone, although the compression ratios were generally too high for my taste.
Next I tried the Gold Channel’s processing on a live recording from a rock-n-roll club. The performance was recorded in stereo to DAT and the client wanted an edited CD, so I needed to transfer the DAT to my computer for editing and mastering. I connected the Gold Channel to the DAT machine’s optical digital output and to the coaxial digital inputs of the computer’s sound card. I love having all those gozintas and gozoutas!
I auditioned several presets, and ultimately chose one called “FM Radio News” which I then tweaked. This preset exercised all the processing blocks, including the Easy Gate, Vintage Compressor, EQ, and Digital Radiance Generator. The resulting recording was far better than the original, as the processors were able to reduce the crowd noise and boost both the bass for punch and the high mids for clarity. The client was happy, and so was I.
That project also let me exercise a clever feature of the Gold Channel called Auto Gain to set the input levels. To use Auto Gain, you simply select the HEADROOM parameter in the SETUP screen, and dial in the amount of headroom you want from 0 dB to 12 dB. You then select the AUTO GAIN parameter and hit the ENTER button. The Gold Channel monitors the inputs and sets both the pad and channel gain for the maximum level, less the amount of headroom you selected. This process ensures that you get as much level as possible into the machine to utilize all the bits in the A/D converters.
IMPRESSIONS
The Gold Channel is a very powerful voice processor. Like any power tool, it is possible to make some unpleasant noises by using its processors to excess. But used in moderation, the processor blocks sound exceedingly good and decidedly un-digital.
In particular I liked the compressors and the Digital Radiance Generator. The compressors sounded much more analog than most digital compressors I’ve used. The Digital Radiance Generator reminded me of a BBE processor, and used with discretion it added a bit of warmth and sparkle that was most pleasant.
I found it a bit difficult at times to navigate through all the options and controls in the DSP sections. I was sometimes unsure whether to grab the PARAMETER knob or the VALUE knob to tweak a function, and I often grabbed the wrong one. However, there are an amazing number of controls in the processor blocks that have to be available for tweaking, and given the limited space on the front panel I’d say TC has done a reasonable job with the user interface.
The Gold Channel is a product that screams for PC editing software. It would be really nice to be able to connect the Gold Channel to a computer and see a representation of all the processor blocks on one screen. Since the Gold Channel has MIDI, might it be possible to have such a program at some future time?
TC Electronic has done a good job of marrying their DSP expertise with a clean microphone preamp. The result is an excellent and complete microphone-to-recorder signal path. There are some distinct advantages to getting your audio into the digital domain as early as possible and keeping it there. The Gold Channel accomplishes this, and gives you a collection of useful processing tools as well.
The retail price of the Gold Channel is $2,495. For more information in the US, contact TC ELECTRONIC INC., 790-H Hampshire Road, Westlake Village, CA 91361. Phone (805) 373-1828. For more information worldwide, visit www.tcelectronic.com.
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