Roger Mayer is probably best known here as the electronics engineer who made effects pedals for Jimmy Page, Jeff Beck and Jimi Hendrix back in the 1960s. But his move to the USA in 1969 to form his own recording-studio equipment company means that, in America, he is at least as well known for the limiters, equalisers and noise gates that found their way into major recording studios during the 1970s and 1980s. In 1989, having successfully reissued the Octavia (famously associated with Hendrix) and launched the Rocket series of guitar pedals, Mayer returned to England and has since specialised in developing and manufacturing an impressive range of guitar effects that now numbers over 20 models.
The RM58 features the proprietary FET-based feed-forward gain-reduction circuit that Roger Mayer originally developed back in the late 1960s. A FET (Field Effect Transistor) is a type of transistor that behaves in a similar way to a triode tube, and it enables circuit designers to achieve attack times that are, in general, much faster than those that can be obtained from vari-mu or optical compressors, making FETs particularly suitable for use in limiting applications. Add in the feed-forward design — in which the gain-reduction control signal is derived from a point in the signal path prior to the gain cell (as opposed to the feed‑back topology, in which the control signal is tapped post the gain cell) and you end up with a limiter that can react to excessive peaks in the signal level extremely quickly if desired.
In the RM58, Mayer developed what he describes as a "dynamically controlled gain reduction" method that, because it can control both positive and negative wave fronts, is able to maintain the centre of a stereo image whilst applying significant amounts of gain reduction. Mayer's FET-based design gives the RM58 the benefit not only of fast attack times but also wide-ranging threshold levels, compression ratios and release times. The eagle-eyed will have noticed the absence of a dedicated ratio control; Mayer explains that, since the RM58's dynamic gain reduction reduces signal levels above the set threshold exponentially in real time, the compression ratio changes continuously, thereby producing a very natural and musical-sounding result. Another benefit of the RM58's limiter acting independently on both negative and positive wave fronts is that there's no latency in the event of a negative peak arriving first at the detector...
All of which brings us neatly on to the attack and release times. The 10 switched attack times are designed to cover a very wide range of recording situations, both in tracking and on the mix bus, and I'm told that they were selected after considering feedback from many famous producers. The 10 release times have been selected to provide, in conjunction with the attack control, many different options, depending on the effect desired, even down to mimicking the behaviour of an optical compressor.
Even the twin VU meters are worthy of mention, since the gain-reduction measurement uses an independent side-chain that is identical to that in the audio gain-reduction path. This ensures real-time accuracy in the display of both the gain reduction and the effects of the attack and release time constants on it. In displaying the input and output levels, the RM58's meters employ custom-designed VU meter drivers and wide‑band meter interfaces to deliver a ballistic response that is accurate to ±0.2dB from 20Hz to 80kHz.
Roger Mayer's 456HD Analogue Dynamics Process is a essentially a proprietary high-speed, non-linear, wave-shaping amplifier that's been designed to mimic the wave-shaping produced by a perfectly aligned Studer A80 24-track analogue multitrack open-reel tape machine, recording onto two-inch Ampex 456 tape — minus all the alignment issues, tape hiss, and wow and flutter. Everyone who engineered back in the days when analogue multitrack tape ruled the roost quickly learned to manipulate the levels going to tape in order to produce tape saturation (compression) and low-order harmonic distortion, both of which, when used with care, can enhance the sound of a track.
Roger Mayer's inspiration for the 456HD process apparently came from listening to early CDs that had been transferred from analogue masters (remember the AAD — analogue recording, analogue mastering, digital conversion — designation on early CDs?) and recognising the enhanced fidelity that this approach can deliver... provided that the transfer isn't done from the vinyl cutting master! Mayer has a theory that the enemy of ultimate audio fidelity when recording digitally is the anti-aliasing filter that sits in the signal chain before the A-D converter, and that using the 456HD process to control and shape each positive or negative peak gives the engineer the confidence to use the maximum possible digital range to obtain the best resolution and quality, as the process can limit the inter‑sample peaks that DAW peak meters are unable to display.