Tape noise reduction - confused...

Well, first you have to be clear on what you mean by "tape noise reduction". The quote you posted above did not refer to an actual tape noise reduction system that might be found in a professional type recording studio, it's a consumer device.

Its purpose was to take the signal from a commercially distributed disk recording, expand that signal with the circuity from the dbx 118, which was the consumer hi-fi version of the dbx compressor/expander device, run it through the noise reduction circuit of the dbx 122, another consumer device which used a compressor triggered by impulse noise to remove already recorded noise from prerecorded signal providing an add-on, single ended noise reduction system. The combination of the two circuits was claimed to produce lower signal to noise with greater dynamic range than the original disk recording. It did work after a fashion with great effect to impressionable listeners but after a little while the artifacting could become obvious.

dbx noise reduction was never really accepted in commercial studios although it was fairly popular on prosumer equipment.

Real tape noise reduction systems (typically Dolby) worked by pre-encoding the signal via frequency-shaped compression before recording to the master, then playing it back through an expander circuit* employing the inverse of the frequency shaping. This type of double ended processing, if properly aligned, could result in significant noise reduction. There were several types of Dolby systems. The ones used on  master recorders used severa different bands of companding, which had to be aligned perfectly in a process similar to alignment of the multi-track tape machine itself. There were simpler ones used in consumer cassette machines the had only one band, affecting the bandwidth of tape hiss that were pre-set at the factory. Commercially produced prerecorded tapes came Dolby encoded; if a Dolby tape was played the effect was more top end due to the high frequency compression.


There was another tape noise reduction technique that pre-dated companding based systems that required no additional hardware than the normally found in the studio and still provided about 6dB of noise reduction. This was simple high frequency pre-emphasis of the signal. The signal to be recorded was boosted by 3dB by a shelving filter at a specific frequency. On playback a 3dB cut was applied,. which resulted in essentially flat response for the signal but a 6dB reduction in tape hiss. Many engineers actually continued to favor this technique after Dolby became widely available due to the lack of the requirement of a complicated and time consuming alignment technique and the fact that it could be used in any multitrack facility without special and expensive equipment.


* - this is downward expansion, in which lower energy signal is made even quiter, not upward expansion in which loud signals become louder.

There was also Dolby-C. As far as I know, it was only on cassette machines, but could theoretically work on any sort of tape. Dolby-C worked on the assumption that high-frequency signals in the material would actually provide some bias in the tape circuitry. So when there was enough HF in the music, the bias portion of the record circuitry was lowered. This lowered overall distortion (and of course distortion is noise). It was a single-ended process and was perhaps the last gasp of trying to improve cassettes.

Regarding DBX noise reduction, there was actually a classical radio station in the Boston area (WCRB) that broadcast DBX-encoded music for a time. It was on the assumption that homes would have a DBX decoder in the playback loop of their receivers. This would get around the limited dynamic range of FM radio. And since DBX was a Boston company in those days, it would result in increased sales for the home team. Didn't really help. DBX even had a record label and released a handful of encoded LPs. That didn't help either.

Good explanation by John!  I will add that aligning a SR encoded 2" machine is exponentially more complicated than aligning the tape machine alone.  Quite the chore.  And patching one in.......  $#@%@^$#@%#!!!!  We used to rent them on occasion for a client and it's a nightmare of cabling going into the TT bays.  Not a fun time....

They DO work though, although they also imprint a sonic fingerprint.  And they were incredibly expensive back in the day.  If memory serves, over $30k for 24 tracks?  Nice, but the hassle factor made me pass on one that was almost being given away.  (Around $1k after digital decks started appearing).  Thanks for the (unfortunate) memories....  haha!

I would love to answer to that one but we would land in politic land and that is a no go on RGO.

>Technology and the devaluation of music via piracy and streaming have everything to do with it.

Yeah, and all the contemporary competition for the entertainment dollar. Audio compositions and performances aren't appreciated and valued today the way they were 20 years ago. 

Hard to find a 'man' to blame, unless it's Al Gore, for inventing the internet.