FIG. 1: Rane's C4 Quad Compressor offers four channels with independent compressor, limiter, and de-esser controls and stereo linking.
Rane Corporation has created a unique combination of technologies with its new family of analog-controlled digital processors. The company's new addition to the family — the C4 Quad Compressor — is, like its G4 Quad Gate sibling, a 4-channel device with all-analog I/O and analog-style controls. (For a review of Rane's G4 Quad Gate, see the July 2004 issue of EM, available online at www.emusician.com.) The unit's internal processing, however, takes place in the digital domain.
The C4's front panel (see Fig. 1) contains four identical sets of independent compressor, limiter, and de-esser controls. All four channels can be used independently, and channel pairs 1-2 and 3-4 can be linked for stereo operation.
When two channels are linked, an LED above the Link toggle switch glows green, and the left channel (1 or 3) functions as the master. Compression results are based on the summed input of both channels. Limiting results are based on the hotter of the two linked signals.
A multifunction LED array at the top of each channel section indicates gain reduction levels and levels below the set threshold. When the signal level is below the threshold, the green LEDs light up, indicating values between -12 and -1 dBr. When the signal reaches the selected threshold value, a central amber LED lights up. During compression or de-essing, the red LEDs light up for gain reduction values between 18 and 1 dB.
Each panel quadrant contains three rows of three knobs. All knobs are plastic with a raised pointer clearly outlined in white, and all parameter values are continuously adjustable. The top row of gray knobs governs basic compression settings. On the left is a large threshold knob. Ratio and makeup gain controls follow.
Below that are three black knobs that cover secondary compressor functions such as attack, release, and variable knee. When the release dial is rotated fully clockwise, a green LED indicates that Rane's auto-attack/auto-release program mode is engaged.
The C4 grants users a great deal of control over the sidechain signal. Few affordable compressors have the C4's combination of external sidechain input, built-in de-essing, and complete parametric equalization of the sidechain signal.
Parametric EQ settings for the sidechain control circuit — dubbed PEQ by Rane — are located on each channel's bottom row of black knobs. Bandwidth (0.5 octave to 10 octaves) is on the left, followed by frequency (20 Hz to 20 kHz) and gain (-12 to +12 dB with a center detent at 0 dB) controls.
A three-position toggle switch to the right of that row determines the channel's meter status and output mode: compressor, sidechain listen, or de-esser. Accompanying LEDs glow green, amber, or red, respectively. When the Listen mode is selected, the amber light blinks as a steady reminder that the sidechain signal is being auditioned.
Sidechain EQ can be used to boost or cut particular frequencies, thereby making the compressor's broadband response more or less sensitive to a specific frequency range. That technique can be used to reduce the low end on a drum track or rhythm section, so that strong bass signals don't trigger extreme attenuation or pumping.
In the De-essing mode, bandwidth, frequency, and compression threshold settings are adjusted to compress only the desired EQ range in the C4's audio output. That dynamic EQ process not only suppresses vocal sibilance, but it also attenuates an unwanted frequency peak in any type of instrument or signal.
With Sidechain-listen selected, external sidechain signals or any changes to the EQ of the triggering circuit can be auditioned through the channel's audio output.
FIG 2: For each of its four channels, the C4''s rear panel has analog inputs and outputs on both XLR and 1⁄4" TRS jacks and 1⁄4" TRS external sidechain inputs.
An additional gray knob controls the limiter threshold (-40 to +22 dBu). The limiter is a digital brickwall type and is set with an instantaneous attack time, a 25 ms hold time, and a 6-dB-per-second release time. A five-position LED meter indicates headroom before limiting (24, 12, 6, and 3 dB) and active limiting (0 dB). The meter does not display the amount of limiting gain reduction.
An active-bypass toggle switch in the upper-right-hand corner controls the compressor/de-esser circuitry. The bypass does not affect limiting or metering and must be switched individually on both master and slave channels when stereo linking is selected.
The C4's rear panel (see Fig. 2) has analog input and output for each channel at a +4 dBu reference level. External sidechain inputs for each channel are grouped on the right. A standard IEC AC power-cord connector is also on the back panel. The unit has no digital audio I/O, a provision for analog -10 dBV audio levels, or an on-off switch.
The C4's two-rackspace all-metal case has adequate ventilation. The C4 uses 24-bit, 48 kHz A/D/A converters. Latency is low (1.2 ms), distortion and noise are negligible, and headroom is satisfactory at a +22 dBu maximum output.
The manual is outstanding. It provides thorough information for users at all levels. It also includes the company's expert manual on sound-system interconnection and wiring.
ON THE JOB
After a few weeks of testing, I came to fully appreciate the C4's range of features and sonic neutrality. The C4 goes about its work quietly without a characteristic sound or attitude.
While switching between Active and Bypass modes, there was no noticeable difference in the audio. Signal muting, switch clicks, or gain changes were not evident.
On some mixes, when I compared two identical mono signals that ran from a TC Electronics M2000 to the mixing board — with one signal feeding the C4 before the mixer — the C4 exhibited only a slight attenuation of low-bass frequencies.
The C4 stood out at processing rock-drum overhead mics in Stereo-linked mode. With careful adjustment of ratio, attack-release, and knee, the C4 squashed a fast drum track while keeping transients intact and adding a slightly aggressive edge to the sound. PEQ sidechain adjustments to a full drum mix made it possible to emphasize or downplay various parts of the kit.
While stereo linking always worked well, I ran into one latency-related problem when using the C4 on one channel of a stereo guitar amp signal. Because of the slight processing delay, the compressed channel lagged behind and lost presence when the two tracks were hard-panned. That problem and its related phase cancellation were easily remedied by running both guitar tracks through the C4.
The C4's continuously variable knee parameter allows subtle yet effective refinement of the compressor's behavior at and around the threshold point. I generally favor soft-knee characteristics and welcomed the variable knee parameter. During studio testing on a trumpet track, the variable knee control was just as crucial as ratio and attack for fine-tuning the compressor's character and keeping the soloist sounding natural and on top of the mix.
I liked the C4 on kick drum but would prefer an attack time faster than 25 ms for that job. On a direct Fender bass track, the C4 allowed enough control to keep the bass where I wanted it in the mix. But again, a faster attack time — for example, a standard 10 to 15 ms — would help control peaky bass transients.
The C4's sidechain EQ feature came in handy on a female lead vocal. The singer had a wide range but tended to push her head voice far above the level of her lower registers. The C4 was able to hold her voice perfectly in check, as a result of boosting a narrow notch around 3 kHz on its sidechain PEQ. The C4 helped to bring out vocal intelligibility and detail without noticeable coloration on a male vocal track as well.
There was a remarkable lack of coloration or distortion on heavy rock guitar, even at a steady 8 to 12 dB of gain reduction. The C4's limiter circuit also gets a thumbs-up for transparent and undistorted continuous peak limiting of a full-range blues mix. For these extreme applications, the C4 treats audio like a quality computer plug-in, while offering the convenient control of analog gear.
The C4 impressed me as a versatile and consistently solid performer in recording sessions. The unit's A/D/A conversion quality is excellent, and the brickwall limiter works like a charm at moderate settings. My only quibble was with the unit's minimal attack time of 25 ms, which is too long to effectively grab transients on many sources.
The C4 is easy to set up, and its generous set of parameters makes it an ideal problem solver. For $999, anyone who is after the most bang for the buck has to be impressed by what Rane has accomplished with the C4. With its smooth audio quality, bountiful features, and rugged build, the Rane C4 acts like a world-class compressor. The only thing missing is the world-class price tag.
Myles Boisenis head fader jockey at Guerrilla Recording and The Headless Buddha Mastering Lab in Oakland, California.
C4 Quad Compressor
FEATURES5.0EASE OF USE4.5AUDIO QUALITY4.5VALUE5.0RATING PRODUCTS FROM 1 TO 5
PROS: Extensive feature set. Parametric EQ of sidechain signal for compression and de-essing. Very low coloration. Useful brickwall limiter. Internal 24-bit, 48 kHz processing. Informative manual. Competitive pricing.
CONS: 25 ms minimum attack time is slow for some uses. No digital I/O. No provision for -10 dBV level operation.
Analog Inputs (4) balanced ¼" TRS, (4) XLR Analog Outputs (4) balanced ¼" TRS, (4) XLR Sidechain Inputs (4) balanced ¼" TRS Sampling Rate 48 kHz internal, not selectable Word Length 24-bit internal, not selectable Internal Processing 48-bit Makeup Gain Range -12 to +12 dB Frequency Response 15 Hz-20 kHz Gain Reduction 18 dB maximum Threshold -40 to +20 dB Compression Ratio 1:1 to 10:1 Attack Time 25-500 ms Release Time 25 ms-2 sec. Dynamic Range 106 dBA Distortion (THD + Noise) @ 0 dB Input 0.02% (20 Hz-20 kHz), 0.006% (1 kHz) Dimensions 2U × 5.25" (D) Weight 7.3 lbs.