LA Audio Classic II Dual Compressor
By Barry Rudolph
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Mix Magazine "Compression And Compressors"
Living up to the name "classic" is no easy task considering that today only a handful of old recording equipment is revered enough to be called classic. The LA Audio Classic range of audio products, manufactured by SCV Electronics in London, aims to recapture the sound, spirit and whole design attitude exemplified by those few select vintage pieces. This philosophy may not be outwardly apparent at first glance, but after my first session with the Classic Compressor II, I found myself as comfortable with its dependable performance as with any "good ol'" UREI 1176 or Teletronix LA-2 compressor.
To begin, the Classic Compressor II is a 2-channel compressor in a road-worthy, 2-rackspace steel cabinet. Cosmetically, the unit's blue anodized aluminum front panel is all business with its brushed silver-gray silk-screening, full-sized controls and standard, lighted VU meters. This is easy on the eyes and refreshingly demure considering the current fad of garishly painted and oddly named outboard equipment. Audio connections on the rear panel are via gold-plated XLRs (pin 2 hot). The rear panel also has a single switch for +4dBu or -10dBV operation, but no unbalanced 1/4-inch jacks. The schematic reveals that this single switch changes both the input and output levels together. There are two TRS jacks for insert send and return paths for external connection to each channel's sidechain.
Both of the Classic's channels may be used as two individual mono compressors or linked for stereo operation. The unit has two complete sets of controls for each channel. They are located one above the other just like an analog 2-track tape deck. I like being able to adjust the two channels separately; I find that ganged stereo output pots are never spot-on together. You can individually adjust input trim level, output level, and interesting to me, the compression ratio.
The Classic Compressor II uses a discrete, FET (Field Effect Transistor) gain control circuit, just like the famed UREI 1176LN peak limiter/compressor. IC operational amplifiers type 5532 are used throughout otherwise. The Input Trim Level control provides a range of +20dBu and -20dBu with a center detent position of 0dB. It is like the input control on the 1176, adjusting the amount of compression and the throughput gain of the compressor at the same time. On the Classic, the input trim can be used in the same way when you set the Threshold at 0dB. Increasing the input trim control pushes more level into the detector and therefore more compression occurs. At +18 dB you will start to overload and a small red LED clip indicator will glow. Maximum input level is +20 dBu. More typically, the Input Trim Level control is used to match the output of the preceding device to the input needs of the Classic II. I usually left it on the 0dB detent position for optimum headroom and signal-to-noise ratio. I like and understand the interaction between the Input Trim control and the Threshold control because this is the point where you can alter the compressor's process and the nature of the compressed sound by "artistically" juggling the input level with the threshold control setting. In the context of certain record production styles, the record level is set by input level/threshold settings for the amount of overcompression du jour.
Probably the "correct" way to set the onset of compression is to use the large Threshold knob with its range of -40 to +20 dBu at fully CW. This is a smooth-feeling pot with a large white pointer. The Ratio knob is similar, but instead of a pot, a six-position rotary switch is used. The available compression ratios are: 1.5:1, 2:1, 3:1, 5:1, 10:1 and 20:1. I like the switch for resettability, and it covers all the ratios anyone could want. Next are the Attack and Release controls. Both are marked the same way, with Fast at fully CCW and Slow at fully CW; the attack ranges from 0.4 ms (fastest) to 40 ms (slowest but still kinda fast for certain applications), while the release times are from 40 ms to 4 secs. The final control is output level, a make up gain control with a good center detent position of 0 dB and an operating range of -20 to +20 dB. Maximum output level from the fully balanced transformer output stage is +20 dBu into a 30-ohm load impedance. Total harmonic distortion is measured at less than 0.5% when the Classic is under 6 dB of compression. Frequency response is specified to +/-1 dB from 20 to 20k Hz, while noise is measured at less than -83 dB.
The Bypass button, when pushed in, connects the input XLR to the output XLR connector and lights up a red LED. This relay-controlled hardwired Bypass circuit is also used when the Classic is first turned on. A turn-on delay time is initiated before the compressor passes audio to prevent any nasty thumps getting to your monitor speakers. Americans may find it odd that the Bypass button is pushed inward instead of outward. We Yanks are used to pushing a button in for Process On and releasing it back out for Process Off. (We also drive on the "right" side of the street.) There are separate Bypass buttons for each channel as well as separate gain reduction/output meter switches. The GR/Output switches toggle the medium-sized analog VU meters between the reading output level and the RMS amount of gain reduction. I would suggest substituting a three-way switch here to include measurement of the input level to the detector as well. Incidently, all of the Classic's controls and functions operate while the unit is in Bypass mode. This is good for making ballpark settings before insertion.
A link switch unites the two channels' detectors, with Channel 1 becoming the Master and slaving the Channel 2 compressor. I would suggest that both Bypass and GR/Output switches for Channel 2 also be grouped together with Channel 1's Bypass and GR/Output switches when in stereo link mode. Overriding whatever previous switch positions on Channel 2 would avoid confusion as to whether one channel is bypassed or if its meter is indicating output or GR.
Included within the Classic II is a broadband de-esser, with 12 dB of attenuation at the center frequency of 8 kHz. The manual states that "all frequencies are compressed in response to sibilant frequency detection" and advises using high threshold and ratio settings along with a fast attack for proper de-essing. These settings would affect the rest of the audio envelope as well, which may or may not work for you. Ultimately for best de-essing, the manual suggests connecting an equalizer in the sidechain insert and "tuning" it to the exact `ess' frequencies. I found the de-ess function to be great for a squashy cymbal sound when I strapped the Classic across a pair of drum overhead microphones. That 8kHz boost caused the compressor to clamp more on cymbal crashes than the tom-toms and rest of the kit. Cool drum sound!
I also used the Classic on vocals, guitars and bass guitars. I liked the way it pushed backing vocals right up close, even with a minimum (3 dB RMS) of compression. This is a good limiter for sample processing where you would digitally transfer your samples directly to your sampler or DAW. Using a heavy amount of compression on electric guitars achieved a density that was perfect in the mix. I also tried some wacky extreme settings for compressed room mics and drum sound treatments, and the Classic did what I wanted without too much distortion and noise.
I liked the fact that both sets of peak indicators have a large amount of hysteresis or lag time before the LED goes out after detecting a peak. Usually I'm not looking directly at the meters when I might hear a possible overloading peak. There is enough time here to catch the LEDs fading out.
The Classic Compressor II was shipped to me with an optional 20-bit analog-to-digital converter. The A/D converter is dealer-installed, and SCV Electronics has promised to make it an end-user-installed item soon so you can add it later on at any time. The current chip set used is a Crystal Semiconductor 20-bit stereo converter and two LED peak indicators, mounted between the VU meters, that monitor the analog peak input to the converter.
Combining a stereo compressor and A/D converter is a smart choice for project/home studios where the Classic II acts as an important link between console and semi-pro DAT deck. There are few places in the recording/mixing/mastering chain where a single piece of new equipment would make more of an improvement in the overall, final sound quality of your recordings.
The Classic Compressor II retails at $1,399, and the A/D converter option is $639 extra.
LA Audio is distributed in North America by Audionova, 2083 Chartier Ave., Dorval, Quebec, Canada H9P 1H3; 514/631-5787 or (toll-free) 888/247-8580; fax 514/631-5789. Web site: www.scvlondon.co.uk.
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