Jargon and lingo glossary - Bi to B9.
DC Bias :Introduced shortly after the invention of the wire recorder and simply entails injecting a direct current on to the recording head in addition to the audio signal, but it was found to improve sound quality , however DC bias is not hugely effective and is even less so on tapes than on wire recorders. In an attempt to cut costs some consumer wire and dictation recorders from the 1930’s and 40’s simply placed a permanent magnet beside the recording head to gain the same effect at lower cost.
AC Bias : It was noticed as early as the 1910’s that injecting an alternating current instead of DC could have even better results, however the early state of electronics at the time meant that this was not cost effective, by the 1920’s a number of patents had been issued that proposed a number of AC biasing methods ,these were all using biasing signals inside the audible range, however at the time wire recorders were mostly used as dictation machines and answering machines so the added cost of electronics and license fees to patent holders for only a small gain in audio quality meant that they were universally ignored
The advent of tape recorders however prompted a re-examination of AC bias, the DC biasing techniques were much less effective on tapes than on wire since tapes are grained magnetic recording but wires are solid, this meant in practice that DC bias did improve sound but added noise. A variety of AC biasing techniques were tried but it was not until 1940 when Walter Weber invented the high frequency biasing technique that we start to see modern methods of biasing. Hr. Webers technique used a biasing signal well outside of the audible range and was dramatically better than the biasing techniques by O'Neill, Camras, Nagai et al, in fact it transformed the tape recorder from a voice quality recorder to a superior hi-fi recording device overnight and as early as 1941 German record labels started to use the recorder in preference to a cutter
For further reading see: Cassette recorder technical specifications: Bias.
Pro-audio usage: The term black box is commonly seen in the same meaning as #1 above although #2 and #3 show up from time to time. A black box is in this case is often a prototype lent to you by a manufacturer for testing purposes or a unique device that is rented out rather than sold, conceptually more as a service than as normal pro-audio rental. A typical example of this were early exciters and high end delays in the 1970’s but instead of selling them the manufacturers rented them out by the hour to recording studios, because of the secret nature of the processors they were often rented out as a Wet Hire only, i.e. they came with a technician whose function was not as much to operate the device as to ensure that you did not open it up and copy it.
The other common black box used to be the Producers Black Box, a signal processor and/or occasionally sound generators that record producers and engineers bought with them to sessions as a kind of “secret sauce”. The best known example of this are the devices cooked up by British producer Joe Meek, but his use was archetypical in that he had some extremely simple devices housed in non-descript boxes that he bought with him to sessions, but kept as a closely guarded secret, not allowing anyone else to open them up or use them, and he had a habit of taking them with him if he went for a lunch break or so on.
The most striking thing about Mr Meek’s and other producers black boxes from the 50’s, 60’s and 70’s is how basic these devices were, the most common units found are transducer boxes of some sort although occasionally you will find simple electronic devises that were built up from designs published in electronics and tape recorder enthusiasts magazines, there were even cases of completely empty boxes that contained nothing but 2 jacks and a piece of wire, a bluff reminiscent of Tesla’s decade resistance box that he presented as a death ray.
The transducer type boxes were simple spring reverbs that utilised commonly available springs such as bedsprings, “tap boxes” that are microphone insets in a wooden box that you tapped with your hands or feet to get a sound that replaced or augmented a bass drum sound or acoustic echo and reverb devices that utilised some strange approaches to echo generation such as garden hoses and water filled tins. All of these using home-made or adapted transducers typically made out of cheap microphone insets and small budget loudspeakers. The electronic devices were commonly simple optical compressors and limiters whose specification was so basic that they had a very characteristic “sound”.
These had fallen out of use in the 1980’s but you would occasionally see producers and engineers turning up with a home built “secret weapon” black box or more commonly factory built devices that had either been rehoused in plain DIY enclosures or had all markings scratched off them. These were signal processors that had for some reason not made it into the arsenals of pop musicians or recording studios but were or had been commonly available in other market segments, that includes classic electronic music devices such as ring modulators or more complex AM modulators, barberpole filters and fixed & formant filter banks but by far the most common was the “Organ phaser”, a device that is actually not a phaser in the modern sense but a phased multitap delay line, sometimes with a bit of waveform distortion as well, built for the home organ market (a Roland ensemble effect is a simplified version of this type of effect).
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