pro-audio products

resonance mastering equalizer

A high end stereo inductor based mastering parametric equalizer, that operates and sounds like no other!

REQ mastering equalizer

view bigger picture left side view right side view black face version

design features

inductor equalizer

the resonance factor

The REQ-2.2 mastering equalizer utilises parallel resonant circuits in a clever configuration whereby the bandwidth (Q) of the circuit can be adjusted like an active filter, but without any complex relay switching. The inductor/capacitor resonant "tank" eq circuit runs at a low internal signal level which avoids any inductor saturation effects. The overall result is the sound of real choke based filters with a big open sound, but without the limitation of only a few - or no bandwidth selections as found on traditional choke eq's.

class a amplifier

audio path quality

As you would expect, the REQ uses our BE40 True Class A circuits developed for the MA-2.2 microphone amplifier for superlative audio performance. It also utlilizes our BE44 discrete line driver at the output that acts like a transformer and can respond to balanced or unbalanced loads.

But sometimes you might need a bit more color, so we have included a saturation section that introduces measured amounts of low frequency harmonic distortion via a steel audio transformer driven by a single ended transistor amplifier. The High Pass Filter is placed in the beginning of the eq chain and the Low Band eq section is placed last in the chain. This layout produces the best overall equalizer coherency.

operational beauty

The large knobs and positive feel of the switching make the REQ a pleasure to operate and everything is visually clear when mounted into a console. In total there are 72 frequency choices per channel with overlapping selections across the four bands so you can always find the centre frequency you are looking for. A looping line XLR input and two parallel XLR outputs provide flexible connection options in the mastering control room. Finally, low glare rustic silver finish and retro Elma knobs give the REQ an impressive look in your rack!

controls and functions

mastering equalizerEach eq band has a 12 position switch to select the FREQUENCY and another that selects the BANDWIDTH or shape of the bell shape curve (Q) which is adjustable from 1/3 octave to 2 octaves wide. On the High and Low bands, the BANDWIDTH control reverts to shelf SLOPE control when SHELF mode is selected via the push button switch (but not with the Active Low Band option fitted). The Low and High Mid bands frequency range is changed to alternative selections when the FREQ x2.5 mode is selected. Each band also has an IN/OUT switch removing the band completely from the signal path. The BOOST/CUT control is a 23 postion Elma switch with a range of +/-8dB, with 0.5dB steps up to 3dB then 1dB steps to 8dB. Custom ranges and steps can be supplied to special order.

On the right side of the front panel are the HIGH PASS FILTER and SATURATION controls with their own IN/OUT switches. The overall SYSTEM IN/OUT controls and the power switch complete the picture. The channel A and channel B push button switches (SYSTEM, HPF and SATURATION) can be grouped by holding down any switch for 5 seconds. This means for stereo work you only need to push either the channel A or B switch to change both channels simultaneously. (This feature only applies to units with serial number Q1110 and up).


The REQ is available with a silver-grey or black face plate.mastering equalizer Only the mastering version is manufactured with the recording version now discontinued. There is an option for the Low Band section of the REQ. This option replaces the Choke based eq filter with an Active filter which provides a "tighter" bass sound. This option (the ALB) has come about from requests from some users who work with modern music styles in mastering. The only operational difference between the Active and Choke filters is that in Shelf mode, the Bandwidth control does not work as a slope control and is disabled.

You can also order the REQ with Lundahl output transformers. When fitted, the direct balanced line out is available on the LINE OUT 1 XLR connectors and the transformer coupled output on the LINE OUT 2 XLR connectors. There are two Lundahl options, the LL1517 audio C-core or the LL1684 amorphous core (expensive!).

Ordering model numbers and indicative pricing (excl. Tax)

Mastering version with choke filter low band - REQ-2.2ME | US$7500 | €6680 | £5745 |
Mastering version with active filter low band - REQ-2.2MEA | US$7500 | €6680 | £5745 |
Lundahl LL1517 transformer option (both channels) | US$265 | €200 | £174 |
Lundahl LL1684 transformer option (both channels) | US$440 | €335 | £299 |

The Active Low Band (ALB) cards can be easily fitted to existing units and you can purchase the kit online here.
Download the instructions to fit the ALB cards here.

We have in the past supplied custom front panel finishes, custom mastering boost/cut ranges, please feel free to contact us to discuss your desires! If you are looking for the older REQ upgrade info and the latest (August 2022) power supply improvement it is here.

product review

Audio Animals by Paul Ashmore

Check out the mastering EQ comparison videos from Paul here.

user comments

Stuart Emerson

buzz Audio req2.2 I received my Buzz REQ2.2MEA from SXPro and I'd just like to say that it is quite simply the best EQ in the universe! It enhances the music so that you hardly know it's switched on and yet it is so powerful at the same time. The saturation is just great at controlling the waveform and the options you have given are perfect for all kinds of applications. I tried other EQ's like Massive Passive and the Knif Soma but for whatever reason they didnt work for me, but the REQ2.2 sits so well, it's the sound in my head, the sound i wished for years ago. The Amorphous core transformer option adds a touch of glue and is a great option to have for mixing and tracking. I am so happy!

frequency chart

30Hz 85Hz 215Hz 560Hz 1410Hz 1870Hz 20Hz
45Hz 110Hz 275Hz 710Hz 1780Hz 2360Hz 26Hz
60Hz 135Hz 340Hz 910Hz 2280Hz 3000Hz 34Hz
75Hz 170Hz 450Hz 1150Hz 2750Hz 3700Hz 46Hz
95Hz 210Hz 540Hz 1450Hz 3550Hz 4800Hz 58Hz
120Hz 260Hz 660Hz 1700Hz 4230Hz 5900Hz 70Hz
150Hz 320Hz 820Hz 2100Hz 5200Hz 7250Hz  
185Hz 400Hz 1000Hz 2650Hz 6500Hz 8800Hz  
230Hz 500Hz 1300Hz 3450Hz 8100Hz 10.8kHz  
290Hz 610Hz 1525Hz 4000Hz 10kHz 13.5kHz  
350Hz 750Hz 1880Hz 4900Hz 12kHz 16.5kHz  
440Hz 930Hz 2330Hz 6250Hz 15.5kHz 20.5kHz  


Frequency Response measured with all eq bands on and set flat, Saturation and HPF off = 5Hz to 125kHz +0.2/-3dB
Harmonic Distortion at +10dBu signal level;
Saturation OFF; 100Hz 0.007%...1kHz 0.004%...10kHz 0.007%...100kHz 0.013%
Saturation ON POS-1; 20Hz 1.5%...100Hz 0.07%...1kHz and up 0.01%
Saturation ON POS-2; 20Hz 1.5%...100Hz 0.14%...1kHz and up 0.01%
Saturation ON POS-3; 20Hz 1.5%...100Hz 0.16%...1kHz and up 0.01%
Saturation ON POS-4; 20Hz 1.6%...100Hz 0.17%...1kHz and up 0.01%
Saturation ON POS-5; 20Hz 1.7%...100Hz 0.18%...1kHz and up 0.01%
Saturation ON POS-6; 20Hz 2.0%...100Hz 0.22%...1kHz and up 0.01%
Maximum Input Level; +25dBu
Input Impedance; approx 20k ohms
Maximum Output Level; +32dBu balanced
Output Impedance; approx 70 ohms
Input Common Mode Rejection; (ref 0dBu) 100Hz -65dB…1kHz -65dB…10kHz -60dB
Noise all bands ON set flat; -110dB below max output level (A weighted)
Power requirements 115V/230V selectable on rear panel
Dimensions 4U rack mount, 300mm deep

Specifications are typical of a production unit and are subject to change without notice. 0dBu reference = 0.775 volts RMS.

  Buzz Audio Ltd
  New Zealand
  Ph +64(0)3-577-5597

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