Audio Design Recording | The History of the Compex
Following the Designer Talk interview with Tim Mead, from Q2 Audio, I thought it would be good to get the history of the Compex compressor and how it actually came about. So who better than to chat to Ian Harley, one of the original designers and owner of ADR UK.
KMR : How did you begin designing equipment Ian, were you always interested in the recording side or performance - how did it all started for you?
IH : I was interested in the idea of becoming a recording engineer, and it was just learning on the back of my own efforts really. From college, I actually was working in London at CBS for a while and one day the train I was on stopped at Maidenhead and whilst walking around the town I saw a small company called Audio and Design. There was a music shop below, so I went in and asked if either were looking for anybody to take on, so they interviewed me the next day and offered me a job.
KMR : What were Audio and Design involved with at this stage?
Well, when I joined Audio and Design I was dead keen and extremely interested in what they were doing there as there were a few directors :
John Wright - who later became the designer for IMF Transmission Line Level Speakers and the TDL line of Speakers, which were mainly aimed at the Hifi market. John also was designing a 9” pickup arm - M9BA. This used Mercury contacts to make the signal connections and was virtually frictionless. It became a very successful product and soon to be a bit of an 'audiophile icon' – I might add that in those days we were allowed to use Mercury, raw hard Mercury in 4 tiny baths around a pivot fulcrum in a moat!!
It didn’t last long before legislation came in and took it away, but the pickup arm was extremely successful. We used to demonstrate it with a Decca Mk4 cartridge with the M9BA arm tracking vinyl records between the grooves - nudging it into the ‘trough’ and watch it track the record right across, that's how frictionless it was!
Ted Jordan - who was the designer of the Jordan-Watts loudspeaker using aluminium metal cone technology. Ted actually joined from being the chief engineer at Goodmans, and designed the Audio Design Titanium Coned Loudspeaker TCL15, which we built in a shed behind Queens Street Maidenhead. This was a 15watt full range speaker which we sold mainly to the Hi Fi market and to the BBC.
We had a sales director called Keith Monks, and at the time Audio and Design had started making an original record cleaning machine and he was our salesman for this and Toa PA products. Keith went on to become successful with the 'Keith Monks Record Cleaning Machine' which he supplied to the BBC amongst many other users worldwide. More info: Keith Monks Record Cleaning Machine
KMR : So Audio and Design were more involved in the Hi-Fi world at that stage?
IH : Well our 4th Director was Mike Beville and his contribution was on the recording side offering a Disc Transcription Service. We used to get a lot of trouble with source material from tape recordings which were either too low in level, and noisy, or with uncontrolled dynamics which caused over modulation which could damage the disc cutter recording head, so we both decided to design a limiter to bring up the levels of these poorly recorded recordings and control the peak levels.
This meant we could achieve better constant levels on the disc without the fear of grove knitting as well as safe guarding the cutter head which was very expensive to replace. So we designed a limiter initially really to protect our cutting heads and bring up the levels. Originally this was a diode bridge limiter.
When we returned the transcribed disks to our clients who were mainly Studios and Bands, they would take them round to Record Producers, and we’d get calls from the Labels and Studios asking 'how are you getting such a good sound on the demo disk which sounds louder and better than the original tape recording". Studios were keen to get one of our limiters and we gave up the transcription service and started making and selling these to the recording industry.
KMR : So that was your first Limiter product?
IH : Yes, that's how it all started. As we were in touch with our clients the feedback was that we needed to get in compression, so we moved over from germanium transistors into silicon. We then employed a guy called Alistair Hayslett who was the chief engineer at AMPEX in Reading and on the back of a cigarette packet he designed the first feedback side chain limiter, FET limiter, and I built it.
He designed it up on a Saturday morning and I sat there and built the thing with him, and I got a good grounding in what was needed for designing good limiters and compressors.
KMR : How did the Auto-release design come about?
IH : We further developed the clever 'auto release' technique – which had a double platform release time constant. The idea behind it was when multiple audio peaks activated the compression level it recovered quickly and these peaks (fast release) would contribute to building up the slower release platform. So if you had lots and lots and lots of peaks going through you would slowly build up a slow release time behind it, so when it stopped, the release time was slower than when it started.
It was our original idea, and it's been mimicked since then, but we were the first to use the auto release function and this would have been from the late 1960's.
KMR : So what model of limiter/compressor were you starting with here, and did it look like the familiar Compex at this stage?
IH : The 600 series was the limiter - the 700 series was the compressor. So when we introduced a commercially available product we called it the 760 which was a combination of them both. As the 600 was a very fast acting limiter, it became our peak limiter within the 760 range of products.
Originally the 700 series was in a 3u box which would have been circa 1971-1974 and the first units had custom engraving, but as we started making more we went to a silk-screened 2u box and that's when I also introduced a colour coding scheme for the knobs, which still holds today. We were using Elma switches and knobs on the 3u box, but when we moved over to the 2u box we used Sifam knobs and meters.
KMR : How did the expander get developed?
IH : We were asked by a ton of people who were using tape if we could help them regarding tape noise on multi-tracks, so we looked into expansion. We took the 700 system and turned it upside down, and inverted it and got a 1:2 expander, and if you put a very high feedback around it, it becomes a gate (100:1)
We realised that expanders built using a peak detected threshold would have a problem, miss behaving opening and closing with little control around the threshold so we actually fitted hysteresis around the threshold. That was a major factor as to how our expander worked so well. The threshold level had to fall within a ‘window area’ and nothing would happen in that window area until it got to the top of the window area then it would snap out, this it made it well behaved and really useable, and it would work every time!
So this model became the 760-X.
KMR : Many people may, or may not know that the Helios Desk compressor is your Compex compressor in another format. How did this come about?
IH : Very early on we were supplying F600 style products to Olympic Studios, and our 600s went into a desk Dick Swettenham had designed there. So when he set up Helios consoles in the 1970’s he was taking from us the F700 in what we called an H module (Helios) F700 version.
It had their logo, but it was our module and just visually setup really for them so it didn’t stand out in their coloured consoles. They got put into our pcb frames with a Helios front panel fixed to it and then plugged into their consoles, and they took supply from us on a regular basis.
If I recall the transistors used on the 600 cards were germanium with a low (0.4v) base/collector pd. It wasn’t long after this that we started making the pc tracked cards to the F600 silicon transistor design that Dick Swettenham used in his early Helios desks ( F600 circuit Mk1).
F600 Mk2 was a redesign that followed closely the same design principles of the F700 series.
Mike Beville got to know Dick very well and became a good friend. During the late 1970’s when Helios ran into financial troubles, we gave their production team some of our ADR products to manufacture like the F300 modules, which was part of our ADR SCAMP modules design. (Standard Compatible Audio Modular Package)
KMR : With the Helios compressor layout, is this a reason why you began making the 760N and 760X vertically design, for use in other mixing consoles?
IH : The 760 was similar to the new Q2 Audio 765, we sold loads of the 760's to Air Studios and others, and that was in the DIN standard format 80x40mm size and designed to plug into a console bus arrangement. We did all our product range in the N module format and this was from the mid-1970's but before that, we'd had a C module, which was slightly larger and fitted older console designs.
KMR : Was the Vocal Stresser alongside these other products as well?
IH : We'd also manufactured a switched outboard equaliser known as the E800 model which later became a sweep equaliser known as E900.
Both of these designs were incorporated with a single channel F760 to form a pre, post and side chain function and marketed as the 'Vocal Stresser' under the model numbers F768X-R with switched EQ in the early 70’s. The later F769X-R had the sweep EQ from about 1974 onwards.
We moved over to the 900 series sweep equaliser which was the one we pushed and promoted as people really did like the sound of it, and it was easier to make and support in the field. We also designed in 1973 the ADR P200 and P400 phasers which used photocells to control dynamic comb filters, the P400 was the auto phaser, rack-mounted stereo version and the P200 was a manual vertical plug-in module - very nice sounding units.
KMR : At what point did you become more involved with the running of the company?
IH : After the 3 directors left to go in their own directions earlier on, I moved to a new location with Mike in Reading and carried on building the limiter/compressors. It was then we became Audio Design Recording. I remember I borrowed from my Dad to become a shareholder in ADR, and Mike and I ran the company as proprietor and technical director for the next 30 years. After Mike retired in 1996 I purchased his shares and continued to run the company successfully up to 2006.
KMR : I know that ADR has now evolved into Broadcast specialists and provided consultancy for much of the Broadcast industry, was digital something you always embraced?
IH : Yes, whilst at ADR in the mid-1980’s, in conjunction with York University music department we started to produce one the very first Hard Disk recording systems using the Atari 1040ST. This was called Sound Maestro.
This was way ahead of what anybody else was doing it at the time and we introduced it at the APRS exhibition using a 380MB Harddrive via Scsi..which was massive and gave just 1 hour of stereo recording at 44.1/16bit!
KMR : This must have been at the cutting edge of digital recording?
IH : The problem we found out was it was the editing concept that users found difficult to understand, so I came up with the idea of displaying it like on a scope, with Time versus Amplitude, and as the Atari was very good at graphics it lent itself to produce waveforms in real-time across the screen. Which of course is what we're all used to these days.
Then if you had a moving cursor you could stop and edit anytime - and this is how we introduced it to the public as the Sound Maestro software.
KMR : So this was the original Digital Waveform editor before everything that followed, what happened to it?
IH : Our big mistake was spending too long on designing and streamlining the software to make it more efficient. By then DSP had become available with the Digidesign Session 8 in 1992 and they had Sound Designer, and we had taken the wrong route. We should’ve jumped over to DSP hardware, that was our mistake.
But we did pioneer the whole waveform editing idea, which we showcased at the APRS show!
KMR : Thanks very much for the interview and the history behind one of the classic compressors now being re-issued by Q2 Audio to your original designs.
IH : Thank you!
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