Dolby A: Breakthrough Legacy of the Dolby Noise Reduction Alphabet?

It might be superseded by newer “alphabets” in the Dolby Noise Reduction series, but does Dolby A truly qualify as a “breakthrough legacy” in noise reduction of tape-based recording?

By: Ringo Bones

There is a little-known fact that Ray Dolby of analog audio tape noise-reduction fame did his early work in radio astronomy. In fact his inspiration for his famed series of “alphabets” of noise reduction schemes which later on eventually lifted the lowly Philips compact cassette tape into the realm of high fidelity and earned Ray Dolby enormous wealth – came from his work in trying to extract very weak cosmic signals from background radiation noise. But the question now is, did the first of the series of the “alphabet” of Dolby’s noise reduction systems – namely Dolby A – truly qualify as a breakthrough legacy when it comes to noise reduction in the high-fidelity tape-based recording and playback?

After American open-reel tape recording pioneer 3M studied Jack Mullin’s World War II – era “war booty” -i.e. Helmut Krüger’s open-reel tape recording and playback system used by the Reichs-Rundfunk-Gesellschaft to broadcast both live Orchestral music recordings and Adolf Hitler’s speeches, it was only capable of a dynamic range of 60 decibels and was later deemed “inappropriate” for true high-fidelity sound during the very dawn of the Golden Age of Stereo. Ushering in a series of innovative methods to improve the dynamic range of tape-based recording and playback by increasing its dynamic range / signal-to-noise ratio to make it much closer to sound like a live musical performance.

The Dolby type-A noise reduction system first used during the start of the post World War II studio recorded music trend that compresses certain portions of the audio signal prior to recording. It does not operate on high-level signals. Dolby A uses a side chain operation where the signal is split into four bands, each of which is processed separately. In the pro-audio / studio recording world, Dolby A almost gained a universal acceptance when it comes to recording and mastering in the recording studio.

Some “purist” analog recordings made as relatively recently as during the late 1960s to the 1970s – either of Classical music or studio recorded pop/rock music persuasion – that does not use Dolby A or any other form of noise reduction seem to have developed a cult-like following of achieving a more life-like sound in comparison to their counterparts that used Dolby or other form of noise reduction. And despite these master-tapes possessing slight residual tape hiss due to the fact that these tapes were recording music while run at their highest possible speed, they do seem to cast doubt as to whether we need noise reduction at all when recording in the studio when all that noise reduction does is ruin the naturalness of the recorded sound. And some pop/rock recordings made during the late 1960s and 1970s that don’t use any form of Dolby noise reduction even sound natural despite of the overdubs.

 Surprisingly, some hi-fi enthusiasts were even surprised by the naturalness that resulted when recording onto cassette tapes without any form of Dolby noise reduction, though the cassette tape deck used in this recordings were modified to run at 3 ¾ inches per second – twice that of standard cassette to enable it to record with signal peaks at +10dB on the deck’s VU meters. So there are times that better more natural sounding recordings can be achieved by not using Dolby A or any other form of noise reduction for that matter. Well, at least Dolby A eventually paved way for its “younger brother” that’s intended for home / domestic / consumer applications called Dolby B.