You are here

TC Electronic Gold Channel

Stereo Signal Conditioner By Hugh Robjohns
Published March 1999

TC Electronic Gold Channel

TC Electronic's latest innovation is a dual‑channel mic amp with comprehensive digital processing. 

Best known for their elaborate range of digital signal‑processing products, including industry‑standard delay lines, multi‑band dynamics controllers and state‑of‑the‑art effects units, TC Electronic have recently turned their attention towards the front end of the recording chain and have addressed the 'tweaky' area of microphone preamplification. But, as might be expected, they have not forsaken their beloved digital technology!

The Gold Channel contains two high‑quality analogue input stages (capable of handling either microphone or line‑level signals) with all the usual facilities, such as pads, polarity reversal, high‑pass filtering and phantom power. After the appropriate signal conditioning, however, the inputs are converted to 24‑bit digital audio signals for all further processing. In true TC fashion, every parameter of the machine can be stored in the 100 user memories and recalled at the press of a button, including all the analogue input settings (gain, pad, filters, phantom power and so forth). There are also 100 factory presets to get you started, with a usable assortment of generic and specific configurations to suit most applications (including many identified by specific classic microphone model numbers!).

The digital signal processing is both comprehensive and familiar. The machine provides an impressive range of selectable facilities, including an expander, a compressor, a de‑esser, a dynamic equaliser, TC's own 'Digital Radiance Generator', an RIAA replay equaliser, a pair of MS matrix encoder/decoders, and useful time‑alignment/delay facilities. The elaborate multi‑band dynamics facilities of TC's Finalizer models are missing, but little else is! The best bit of all is that although the A‑D and D‑A stages are restricted to 44.1 or 48kHz operation, the rest of the digital signal path is capable of supporting 88.2 and 96kHz processing (albeit with a reduction in overall DSP resources), with all the expected sonic advantages.

Guided Tour

The front panel of the Gold Channel is very characteristic of the TC product line. The 1U rackmounting metal case is painted in a silvery grey colour (not gold!) with a combination of clear black and white‑on‑black legends. The controls and facilities are grouped in five distinct areas. Starting on the left is an illuminated push‑button to activate the unit or put it into standby mode, together with TC's standard PCMCIA card slot supporting an optional 999 user‑memory removable RAM card.

The next two blocks provide independent input controls for the two channels, which I'll return to in a moment. These are followed by the usual TC‑style backlit LCD screen, and finally a pair of rotary encoders and associated buttons to navigate the screen menus and alter processor settings.

Unfortunately the review machine was dispatched without a user manual, but it is a testament to the usability of the machine that I was able to discover all of its facilities and operations very quickly. I am in the fortunate position of being pretty familiar with several other TC products, all of which share a very similar operating regime, but, even complete TC novices should be able to figure the machine out without too much trouble, and I expect the Gold Channel's manual to be every bit as well written and helpful as those supplied with their other products.

The Details

The input‑stage controls occupy a large proportion of the panel real‑estate but, despite the number of facilities, retain good ergonomics and are easy to use. Each channel is equipped with a single knob, eight small buttons, four large ones and three bar‑graph meters. The knob determines input sensitivity (as would be expected), but there are no scale markings around it at all. Instead, when either knob is moved the LCD automatically shows a pair of virtual knobs with pointers equating to the position of the real controls, together with numeric readouts of the gain applied to each channel. (This page can also be accessed by selecting the 'Setup' display mode with a button to the right of the LCD panel.) Input source selection is determined by a small push‑button below the gain knob, repeated presses cycling through the three options of Mic, Line and Digital, the choice being indicated on green LEDs.

For microphone inputs the gain spans +40 to +70dB, with selectable pads of 20 or 40dB. The input pad is controlled by another small button to the right of the input selector and a menu option enables a further step of 60dB if required (illuminating both the 20 and 40dB LEDs). With a line input selected the gain range extends between ‑22 and ‑2dB, and the pad circuit is disabled. In both cases an automatic gain‑setting mode is available, with the user simply choosing the amount of headroom required (between 0 and 12dB in 3dB steps) and which channels are to be adjusted — the machine takes care of the rest!

The next button on the bottom row selects a high‑pass filter and its turn‑over frequency. With no LEDs illuminated the filter is bypassed, but on each press of the button the filter is engaged, with sensible turnover frequencies of 60, 80 or 120Hz. The last of the bottom four buttons introduces a soft limiter to reduce the likelihood of nasty noises from an overdriven A‑D converter stage. A green LED shows when the limiter is in circuit and an orange one flashes when it is forced to act. Personally, I preferred the sound of the machine with the soft‑limiter disabled.

The four buttons in the top row have only a single option each, with status indicated by adjacent LEDs. The first button activates 48V phantom power, the next introduces a polarity reversal, the third mutes the signal, and the last reallocates the input bar‑graph metering to the output. This metering consists of a horizontal row of miniature LEDs spanning a 60dB range, the top half providing 2dB increments down to ‑12dBFS.

To the right of these controls, four larger buttons activate the various signal‑processing facilities — Expander, Compressor, EQ and Tools. The first three are self‑explanatory, but the last includes functions such as the de‑esser, dynamic equaliser, Digital Radiance Generator, and RIAA equaliser. There are two options for each of the other processes too: the expander provides an 'Easy Gate' or 'Advanced Expander', there are 'soft' and 'vintage' compressors, and the equaliser is available in 'Easy' and 'Advanced' modes! Double‑clicking on the relevant button recalls a menu page with all the parameters and their values listed. These may then be edited with the two rotary encoders on the right of the machine — the first to navigate the list and the second to alter the value of the highlighted parameter.

Metering is a strong point of the Gold Channel, as this close‑up of channel 1's light show indicates.Metering is a strong point of the Gold Channel, as this close‑up of channel 1's light show indicates.

I am pleased to report that the Gold Channel provides permanent gain‑reduction metering associated with each channel, unlike far too many digital signal processors currently on the market. Two meters are provided, in fact, one for the expander (orange LEDs) and a second for the compressor (red), and these are located just to the left of the processing selector buttons on each of the channel input controls. The meters are crude, offering only four LEDs each to show when the gain reduction reaches 3, 6, 10 or 18dB, but extremely useful nevertheless.

The controls to the right of the LCD panel are dedicated to the business of setting the machine up. Four wide black buttons select the operating function: Program, Edit, Setup or Utility. Program is the normal operating mode, Edit allows the signal processing blocks to be configured, Setup determines the input gain, output gain, signal routing and clocking options, and Utility accesses parameters such as the LCD viewing angle, input pad range, memory protection, a range of subtle user‑interface options, and the comprehensive MIDI utilities.

The first of the two rotary encoders (both of which have a detented action) scrolls around the various options displayed on each menu page, while the second alters the highlighted parameter. Above the two knobs are three more small buttons plus another wide one. The first two small buttons are cursor controls to select sub‑pages in the menus. Each of the four prime functions listed above has three or four menu pages in all, and each of these can have up to about 12 parameters. This may sound daunting, but it is actually very well thought out and easy to find your way around, and uses a friendly combination of simple graphics and text. The last two buttons are labelled Exit and Enter: the former leaves a menu level and the latter confirms requested actions.

The Back End

The rear panel is as busy as that of most TC products. Starting on the left, a miniature rocker switch provides mains power isolation and is accompanied by a standard IEC mains inlet. There are no accessible fuses or voltage switching — the unit incorporates a switched‑mode power supply capable of operating on voltages between 100 and 240V, drawing a modest 20 Watts.

The Gold Channel's back panel features comprehensive analogue and digital interfacing, with the bonus that whichever is not serving as the main I/O can be used to provide an insert point.The Gold Channel's back panel features comprehensive analogue and digital interfacing, with the bonus that whichever is not serving as the main I/O can be used to provide an insert point.

Next along are four XLRs, two female for the balanced analogue inputs and two males for the outputs. In the centre of the panel a pair of TOSlink connectors provide S/PDIF optical digital inputs and outputs (these ports can also be reconfigured via the menu system to send and receive data as channels 1&2 in ADAT format). A lone phono socket provides a word‑clock input and is sited between the optical and wired digital ports. Next are a pair of XLRs providing AES‑EBU input and output and a pair of phono sockets for S/PDIF connections. The usual trio of DIN sockets will keep the MIDI fraternity happy, and the panel is rounded off with a quarter‑inch jack socket for an external output fader control signal.

Internally, the unit is a work of art. The power module is carefully screened to one side, with the large motherboard covering the majority of the remaining floor area. Surface‑mount components are used extensively, and the overall build quality is exemplary.

Signal Processing

The Gold Channel offers a wide range of signal processing, as already mentioned, which makes it a very useful general‑purpose tool to have in the rack. The big advantage of digital signal processing, of course, is that the arrangement of individual processing blocks is virtual rather than physical, and so these notional processing blocks can be re‑ordered as required — allowing EQ pre‑ or post‑compression, for example.

When the Gold Channel is in basic operating mode at 44.1 or 48kHz, up to four processing blocks can be chained for each channel, with the order of expansion, compression, EQ and miscellaneous Tools being left to the user to determine. If required, the input from channel 1 can also be routed to channel 2 as well, either pre or post channel 1's signal processing — a useful facility allowing parallel or serial processing configurations.

When the machine is switched to operate at 88.2 or 96kHz (valid for appropriate digital input signals only) the limited DSP resource can be arranged to provide two channels with a single process in each or, alternatively, up to three processes for a single channel.

The Processing

The 'soft compressor' processing mode provides conventional controls for threshold, ratio, hard‑ or soft‑knee, attack and release times, output gain and the side‑chain input (itself or the other channel). The ability to use the second channel to process the side‑chain signal opens a whole world of possibilities in frequency‑selective compression amongst other weird and wacky ideas! The alternative compressor mode — 'vintage' — is rather simpler and only presents controls for input drive (instead of threshold), output gain, ratio, attack and release times. This makes the Gold Channel generally a much faster and easier device to set up, if somewhat more crude! If the machine is set up with the same processing option in the same place on each channel, the units can be stereo‑linked and adjusted in unison.

The expander options are similarly well specified. The Easy Gate mode provides threshold, 'max damping' (ie. range), 'mode' (fast or slow options which effectively set the ratio between gating or a 1:2 expander), and selection of the side‑chain source. The Advanced Expander option offers parameters for the threshold, ratio, attack, hold, release, hard‑ or soft‑knee, max damping, and side‑chain selection. However, the side‑chain processing goes one better, by including a filter with selectable bandwidth and turnover frequency, as well as a facility to monitor the side‑chain while adjusting it.

There are two equaliser processors available. The first is the 'Easy EQ' designed to mimic the classic valve equalisers of yesteryear. It provides top and bottom filters, swept low and mid bands, and a shelf at the top end. The Advanced Equaliser is a far more complex beast with five parametric bands, each having controls for gain, frequency and bandwidth. The top and bottom bands can also be configured as shelf equalisers with slopes ranging from 3 to 12dB/octave. There is also a global output‑level control and a soft‑clipper function.

In the Tools category, the de‑esser provides facilities for selection of the turnover frequency and threshold, along with the usual side‑chain and monitoring options. The dynamic equaliser provides parameters for the threshold (with relative or absolute settings), frequency, bandwidth (or shelf option), ratio, attack and release times, and the familiar side‑chain facilities once more. The Digital Radiance Generator essentially adds small amounts of second‑ and third‑order distortion, and the only controls provided are a drive level and a positive or negative 'curve' selection (to determine the polarity and audible effect of the induced non‑linearity). The RIAA equaliser has a single parameter to define the response as mimicking the curve defined in 1964, or an updated version laid down in 1987!

With the signal processing selected and ordered, a metering sub‑page on the Edit menu allows the signal levels experienced by each separate processing function to be reviewed as crude horizontal bar graphs within the respective processing blocks, displayed as a graphic. This is an extremely useful facility, as it would otherwise be very difficult to identify the processing module responsible when the machine runs out of headroom!

In Use

The Gold Channel is a dream to use. Once the user is familiar with the TC interface and the way in which the various LCD menus are structured, setting the unit up and editing the processing parameters is child's play. All the information you need is presented clearly and simply — for example, adjusting the EQ is assisted by a plot of the frequency response, and a transfer curve is shown when manipulating the various dynamics functions.

When all the signal‑processing was turned off and the Gold Channel was auditioned as a straight microphone preamplifier, it fared extremely well. It has no discernible character, allowing the sound captured by the microphone to pass directly to the recorder if required. The built‑in A‑D stage seemed to perform very well too, and certainly considerably better than the input stages of the digital console I was comparing it with, although that is hardly surprising given the price.

As a signal processor, this machine has all the quality hallmarks of which TC Electronic are so proud. It's clean and accurate when required, rich and warm with the Digital Radiance Generator, and so amazingly flexible that any possible combination of signal processing can be achieved quickly, easily and effectively. I have always been a fan of TC products, and the Gold Channel has certainly reinforced my view. If you only buy one general‑purpose signal conditioner, I thoroughly recommend you try this one first.

Insert Recycling

A very useful facility, seen on other TC products, is the ability to re‑allocate unused I/O as an insert point. For example, when you're using the digital ports for the main input and output, the analogue interfaces can be configured to provide an insert point pre or post the signal processing. Conversely, with analogue inputs and outputs, the digital I/O can be used as an insert point, or as a direct feed, for example.

Mid Side Story

The Gold Channel's input and output processing is notable in that it offers matrix conversion between two different stereo formats, M‑S and L‑R. For those not familiar with the concept, M‑S (standing for Mid and Side) is an alternative method of capturing or recording stereo signals which offers a number of advantages in certain circumstances over the conventional left‑right format more conventionally used. I was intrigued to find that the Gold channel offers three options: off, M‑S to L‑R, and L‑R to M‑S.

In fact the two matrix conversions are absolutely identical — both involving nothing more than sum and difference combinations to create the alternative signals. With either version of the matrix selected, inputting M‑S signals will result in a decoded L‑R output, and L‑R input signals will generate an M‑S encoded output! Similar matrix facilities are provided on the output and when the two are used in combination, the Gold Channel can be used to process conventional L‑R stereo signals as mid and side, allowing frequency‑conscious stereo width adjustments, for example. The output processing includes panning and time‑delay facilities as well as the M‑S matrix, and a correlator (showing relative phase relationships between the two channels).