Buzz Audio Essence

The  Buzz Audio Essence is a True Class A Optical Compressor designed to fit the API* 500 VPR Series rack frames offering a great feature set in a compact package. The essence will find application with those seeking a musically transparent compressor for all tracking and mixing tasks, and it sounds particulary outstanding when processing voice and bass tracks. The essence - the Heart 'n' Soul of your next recording!
The essence control circuit design is based on the Buzz Audio SOC-1.1 Stereo Optical Compressor but the main audio path utilises our BE40 and BE50 True Class A amplifiers along with high spec Lundahl* input and output transformers. The input transformer is directly coupled to the Buzz proprietary Opto gain reduction element (completely passive input), amplified and then balanced via the output transformer - a very simple but gutsy signal path!

The essence control circuitry utilizes the Differential Drive Side Chain (DDSC) topology that was developed for the SOC-1.1. This system, which processes positive and negative audio waveform in seperate paths, provides the incredibly musical characteristic you will hear with this unit. The DDSC design also provides for a much faster attack time compared to most other LDR based optical compressors.

Simple side chain equalizers have been provided to allow the user to adjust the sensitivity of the compressor at high and low frequencies. In addition, a side chain insert point is provided for more complex EQ and compressor "keying".

The essence consumes 2 slots within a 500 Series rack. The input/output (I/O) connectors associated with the first slot carry the main audio path. The I/O connectors associated with the second slot are used for a side chain insert point (send and return). The insert can be switched in/out of circuit and monitored via front panel switches.

Rack Compatibility
The essence power consumption of 120mA is higher than other 500 series modules, but because this demand is spread over two slots (60mA each) it should work fine in all available racks. For more information on linking two essence units, please read this.

features

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      API* 500VPR Series rack module format - plug in and play!
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      Advanced analogue technology - not a clone or copy of products from the past.
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      Powerful fully discrete hi-bias, wide bandwidth, differential Class A amplifiers.
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      Passive transformer coupled input, transformer coupled output
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      Side chain insert point
    * Side chain monitor selector
    * On board side chain EQ
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      Unique Differential Drive Side Chain design
    * May be linked to multiple essence units within one rack, more info
    * Switchable 10 segment VU meter

specifications

Frequency Response with no gain reduction = 14Hz to 107kHz, +/- 1.5dB
Maximum Input Level = +25dBu
Maximum Output Level = +27dBu
Total Harmonic Distortion
Measured at 0dBu input, no gain reduction, make up Gain 0dB
100Hz = 0.1%, 1kHz = 0.015%, 10kHz = 0.002%
Measured at +10dBu input, 20dB gain reduction, make up Gain +15dB, Attack AUTO, Release 16
100Hz = 0.1%, 1kHz = 0.015%, 10kHz = 0.005%
Residual Noise = -95dB A wtg, 150ohm source Z, make up Gain 0dB
Make up Gain Range = 0dB to +15dB
Maximum Available Gain Reduction = 25dB
S/C HI EQ Boost/Cut = 8dB @ 10kHz
S/C LO EQ Boost/Cut = 8dB @ 100Hz
Main Audio Input Impedance = 20k ohms, bal or unbal
Main Output Impedance = 100 ohms bal or unbal
Sidechain Send Output Impedance = 100 ohms unbal
Sidechain Return Input Impedance = 44k ohms bal or unbal
Sidechain Max Input/Output Levels = +22dBu
Size = (3"Wx5.25"H). Fits 2 spaces in API* 500VPR Series rack format
Power requirements = 120mA +/- 15-18 volts DC, as supplied by rack power supply

NOT A LIGHTWEIGHT UNIT

The densely packed front panel has a large 10-segment LED VU meter, seven toggle switches and five human-sized control knobs that are larger and feel better than the typical knobs used on API modules. Essence's operational precision is evident by the complete set of clearly marked front panel control knobs, including drive (threshold), ratio, output gain, attack and release.

There are switches for hardwire bypass, stereo or surround linking, sidechain insert I/O, sidechain monitor select, high- and/or lowpass filter insert to the sidechain path, and input/output/gain-reduction source select for the level VU meter. The VU can be internally set to read either standard +4 dBu or +14 dBu, with the latter better suited for use with a DAW.

The high- and lowpass sidechain filters have a "B" (boost) position and a "C" (cut) position. These are shelving filters with 8 dB of maximum boost/cut at 100 Hz and 10 kHz, with their corner frequencies both starting at 600 Hz, which is the classic Baxandall topology used in many EQ circuits.

A HARDWARE PLUG-IN

Essence went to work as soon as I plugged it into the studio's API rack. It went right in with no problems; you will have to secure it with screws so that the rear-edge connectors stay firmly seated. Essence pulls a total of 120 mA — 60 mA for each slot — which is well within spec for modern API racks.

My first tests were on individual drum tracks recorded flat into Pro Tools. Normally, I would not use an opto compressor on percussion because usually the attack times (if they are available) are too slow. Essence has a 1ms attack time that was actually too fast! At 1 ms with a 20:1 ratio and the drive control set halfway or higher, the snare hit's "stick" portion was completely removed. This type of special effect is usually associated with compressors that use VCAs or FETs.

The 15ms attack position was more realistic-sounding, producing a nice "pop" with each strike on the drum. Between the drive control setting and the excellent range of release times, you can dial in as much drum ring out as you want. I used the 200, 400 or 800ms positions, depending on tempo and whether the drummer played grace notes or fills between back beats.

On vocals, cleanliness is important, especially if you use a lot of compression. Essence's sound sparkles even using a 10:1 ratio and 10 dB or more of gain reduction. No compressor is transparent, but when I selected proper attack and release times, there were no noticeable bad-sounding artifacts. I used the "C" position on the sidechain's LPF to lessen the amount of compression caused by intermittent plosives and the subsonic low frequencies from my male singer.

Electric guitars sounded good when compressed by the Essence. I'm not generally into "auto" positions, but the auto-release time position worked fabulously on a funky rhythm guitar track. With the attack time set to 15 ms, there is very little dulling, even under about 6 dB of gain reduction. On guitars, primarily a midrange instrument, I used the "C" positions on both the low and high sidechain filters to narrow the frequency bandwidth available to Essence's opto element. This setup produced a dense guitar sound without sounding overly clamped.

For bass guitars, I switched to the "B" mode in the sidechain's lowpass filter to make the unit more sensitive to low frequencies. The result was increased precision: You can fine-tune essence to exactly meet the needs of a bass guitar. Using a 2:1 ratio, 70ms attack and 800ms release, the ultraclean opto sound kept the Fender P bass sounding full and natural.

THE ESSENCE OF UTILITY

Essence packs a lot of easy-to-control power into just two API 500 slot spaces. At first, I had two immediate impressions: It is very clean-sounding and extremely fast for an opto-based compressor. I also liked the solid feel of the switches and knobs, along with the large VU meter that always indicates level and gain reduction, even in bypass. It functions cleanly for smooth and fast compression, making this US$920 unit a first choice for any dynamic processing — from subtle to severe.

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