Feature article
The dbx company manufactures professional audio gear, and at one point had a lot of consumer products as well. Their consumer audio products ranged from dynamic range enhancers and compressors to sub-harmonic bass synthesizers and tape/source switches. They are also well known for their noise-reduction systems, the topic of today's article.

The dbx noise reduction system was used in studio recordings--the type used there was referred to as Type I noise reduction. It was designed for professional equipment that had less inherent noise, such as studio multitrack and 2-channel mixdown recorders. The Type II noise reduction was designed for consumer equipment, primarily with higher inherent noise (like cassettes and vinyl). The two types are not compatible.

The dbx system works by compressing the dynamic range 2:1 on recording, and expanding it 1:2 during playback. (Essentially, compression will make quieter parts of the track not as quiet, and louder parts not as loud; it cuts the differences between loud and soft sounds in half, in other words.) That compressed audio signal more easily fits within the dynamic range of the tape and, upon expansion when the signal is restored, the noise is similarly reduced into the background. Another benefit is that the headroom and total dynamic range is improved--more signal can be fit onto the tape or disc without being buried in noise or overloading (which can cause clipping distortion, where the highest levels are clipped off).

Where Type I and Type II differ is in their frequency response--Type II uses more high-frequency pre-emphasis (a treble boost) during recording, which was then countered with a corresponding high-frequency de-emphasis (treble cut) during playback. The Type II "disc" setting works exactly the same but adds a low-cut filter to reduce rumble and warp frequencies.

Here is a chart showing how the dynamic range is compressed to fit onto a cassette.

dbx explained.png

Dolby's encoding/decoding process is slightly similar, but the two are not compatible. Dolby B, for instance, only provides the compression and expansion on higher frequencies, and by a lesser amount.

Can you play dbx recordings without a decoder? Sure, you can play them, although they will sound terrible. Unlike Dolby B, they cannot be played properly, and are nearly unlistenable, without a decoder.

Drawbacks? There were a couple. As a consumer noise reduction system, dbx was not widely used among manufacturers. Consumers could purchase outboard decoders and at one point when dbx records were being released, dbx introduced a low-cost decoder to use in your home system. (They also briefly offered a 12-volt system for use in automobiles, although it required using a tape deck that operated through line level outputs feeding a separate amplifier--the decoder sat between the tape deck and amplifier.)

Another drawback was sound quality. The biggest issue was the clearly audible "pumping and breathing" of tape hiss behind certain kinds of music. In other words, behind music with very little high frequencies, you could hear the tape hiss pulsing along with the music. A solo piano was very susceptible to this phenomenon. As cassettes were noisier than records, the dbx process worked better on vinyl, as many titles were pressed on virgin vinyl and already had a low noise floor. There were also cases where something didn't sound quite right with the music after decoding, likely due to non-linearity in how the signal was recorded to tape. (In other words, if the tape was not recording the exact dynamic range levels as the signal being fed to it, this could throw off the decoded dynamic range noticeably.) Finally, the pre-emphasis could sometimes overload a cassette deck, causing high frequency distortion.

We should also mention one final noise reduction system. The CX noise reduction was used on records to reduce noise. CX stood for "Compatible eXpansion." However, it worked more like Dolby B, offering only a slight higher-frequency noise reduction, and it could be played without a decoder (hence the "compatible" part of the branding). CX flopped on records (largely due to only one major label, Columbia, adopting it, and ideally requiring an outboard decoder be purchased, just like dbx), but the Laserdisc community found it worked very well, and most Laserdiscs after a certain time were CX-encoded, with players having CX expansion built in.

For a list of many of the dbx-encoded records released, you can find one at Discogs:


For posterity, there are a few dbx encoder/decoder model numbers. Models 122, 222, 224 and 224X were two-channel encoder/decoders; the model 224 (and presumably the 224X) allowed you to monitor the output of a 3-head cassette deck to monitor the signal in real time. The model 124 was a 4-channel encoder/decoder. The model 128 included an encoder/decoder as well as an audio dynamic range compressor/expander, and the newer model 228 only the dynamic range expander; these were used to improve the dynamic range of any input source. The model 21 was a decode-only unit. The NX-40 came along when dbx discs were being released, but had its circuitry reduced to an inexpensive integrated circuit and therefore suffered a little in sound quality. The model 22 was the 12-volt automotive model.

The dbx units install in the tape monitor loop in your amp or receiver.


The dbx 22:

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The dbx 21 decoder:

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dbx 122:

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dbx 222 and 224, from the 2nd generation 200 series, with optional rack mount ears:

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The once-inexpensive NX-40 IC-based encoder/decoder. The model 22 automotive version above was based on the same IC.

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The dbx 128. The left half is the dynamic range expander/compressor, and the right half the Type II encoder/decoder. Basically a dbx 118 and 122 combined.

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Note that a model like the 3BX was a dynamic range enhancer; the "3" indicated three bands of expansion (lows, midrange, highs). These were not dbx noise reduction units.

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Also, units like the dbx 150 and 150X were in their professional line, and were Type I noise reduction units used primarily in studios. They do not have the needed pre-emphasis/de-emphasis needed to properly play back Type II tapes and discs. These all had front-mounted calibration controls. Here is a stack of 150s and a 150X.

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Do you own any dbx-encoded LPs? Let us know if you have any in your collection, or if you have any questions or comments.
 

Mike Blakesley

Well-Known Member
Staff member
Moderator
Wow, I had forgotten all about dbx. That was cool tech for its time. I remember people being pretty stunned at how good those albums sounded on a good stereo system.
 

Rudy

¡Que siga la fiesta!
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The LPs were nearly silent, yet there was always something just a little off about the sound. It had this faint, odd "closed-off" or "stuffy" sensation that is hard to describe. Yet I found it worked better on LPs than on cassettes--the pumping and breathing (as it was commonly called) made me go straight back to Dolby after a few tries with it. Think of hearing bursts of hiss every time a piano note would play--it is very distracting, and something I never heard on LPs. dbx worked properly in a studio environment (under the Type I system), as the noise floor of professional equipment and high tape speeds meant it could perform well. The theory was sound, but the application of it varied.

Dolby B never really impressed me that much, but it was a compromise due to car players having the ability to play them correctly. At home, Dolby C was an improvement. Some these days claim that Dolby wasn't any good, but few owned cassette decks where the Dolby level could be calibrated prior to recording. With that and proper bias adjustment (both made easy by test tones generated on the tape deck), the cassettes could sound fairly good. I always got raves for the TDK D-90 cassettes I used to share--everyone assumed it was a cheap tape that sounded mediocre, but it has more to do with the quality of the deck vs. the tape.
 

Harry

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Dolby B never really impressed me that much, but it was a compromise due to car players having the ability to play them correctly. At home, Dolby C was an improvement. Some these days claim that Dolby wasn't any good, but few owned cassette decks where the Dolby level could be calibrated prior to recording. With that and proper bias adjustment (both made easy by test tones generated on the tape deck), the cassettes could sound fairly good. I always got raves for the TDK D-90 cassettes I used to share--everyone assumed it was a cheap tape that sounded mediocre, but it has more to do with the quality of the deck vs. the tape.
Indeed. My last cassette deck from, I think, the early 90s, had Dolby B, C, and S. I could swear that the Dolby S setting was just amazing, but never had any place to play them back properly, other than at home, on that deck. But that defeated the portability of the cassette medium, so I ended up using old, slightly wonky, Dolby B. It sounded best in the car.

That Sony deck also had three heads and real-time tape-bias adjustment, so the tapes I made always sounded pretty darned good.
 

Bobberman

Well-Known Member
Dolby B never really impressed me that much, but it was a compromise due to car players having the ability to play them correctly. At home, Dolby C was an improvement. Some these days claim that Dolby wasn't any good, but few owned cassette decks where the Dolby level could be calibrated prior to recording. With that and proper bias adjustment (both made easy by test tones generated on the tape deck), the cassettes could sound fairly good. I always got raves for the TDK D-90 cassettes I used to share--everyone assumed it was a cheap tape that sounded mediocre, but it has more to do with the quality of the deck vs. the tape.
My old Panasonic rack system with its dual cassette recorded stuff very well at least the quality for me was the best I ever experienced at that point keep in mind it was 1987 even normal position maxells and Sony and other brands of blank tape sounded Very excellent to my ears although I was much poorer back then I felt I was living in an audiophile dreamworld then came CDs and eventually The CDR which replaced Cassettes completely I still have one working cassette deck for transferring tapes to disc ( with a CD I can rip it immediately into my computer audio library) I still keep my mind open to buying some cassette albums that never seen a digital release of any sort and that's a rarity but then so are those particular recordings
 

Electroliner

New Member
I have a 22, 222, and 224. I also own an external PPA-1 unit that I used for my original Sony TPS-L2 Soundabout(Walkman).

The only DBX Disc I own is Gino Vanelli's Brother to Brother that was issued by Nautilus Records.
 

Rudy

¡Que siga la fiesta!
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Thread Starter
The only DBX Disc I own is Gino Vanelli's Brother to Brother that was issued by Nautilus Records.
I still have maybe four or five at the most, but got rid of over a dozen others. They just never grew on me. I think the only Nautilus dbx I had was Zenyatta Mondatta (The Police). Of my remaining titles, I still have a couple on the RealTime label (which were recorded digitally)--those classical titles sounded really good, and aside from a CD or two, some of those works were never released digitally, so I want to hang onto those.
 
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