Monday, February 11, 2013

The 1980s “Digital Decade”: The Decade That Sound Quality Forgot?


Many innovations born during this time eventually made our present day hi-fi a relatively affordable hobby but were the 1980s truly the decade that the concept of sound quality was forgotten?

By: Ringo Bones

Back in the time – i.e. the late 1970s - when “experts” believe that the residual noise in a system with a 70 dB signal-to-noise ratio measurement is already inaudible to most humans, the birth pangs of the “digital decade” cried out a promise of perfect sound forever where all it did achieve was “consistent sound forever” digital master recordings were touted as the best thing since sliced bread. Back in 1980 – a digital recording system whose specifications are a “bit” less advanced than that of the one used in recording CDs by 1983 – were used to make hiss-free master tapes for later vinyl LP release, as in “digital vinyl LPs.

Strangely enough, the JVC DAS-90 digital recording system, whose specifications are a bit lower than that of the Redbook spec 16-Bit 44.1 KHz sampled digital later used by consumer electronic giants Sony and Philips to record and master their music for CD releases when 1983 came resulted in vinyl LP releases of mostly Classical recordings that have way better sound quality than CD. Back in 1995, an audio-buddy of mine upgraded his cartridge to a more expensive Transfiguration Spirit to find out what the digital audio artifacts of the JVC DAS-90 mastered digital recording sounds like. It was a Classical vinyl LP of Weber’s Clarinet Quintet from the American Nonesuch label. And he apparently only got a better sounding set-up as a result – as in a better quality analog sounding set-up. So is digitally recorded vinyl better than the Redbook spec CD? During the mid 1990s – such questions and actual side-by-side vinyl versus CD experimentations only add fuel to the fire to the digital versus analog debate.  

The mid 1980s was also the time when I started my first forays into serious hi-fi. Even the contemporary major releases of the time were full of hype about the benefits of digital audio recording and mastering. During the time, Sony 32-track open-reel digital recording machines and its attendant 32-track digital mixer and the 32-track digital mastering machine working at the Sony-Philips Redbook spec of 16-Bit 44.1-KHz sapling were probably the de rigueur of most major label releases. Well at least Judas Priest’s Turbo, Scorpions’ Love At First Sting, Mötley Crüe’s Girls, Girls, Girls and Heart’s Bad Animals were the albums that landed on the upper echelons of the Billboard Charts while being flogged as full digital recordings. And you know what – they are apparently indistinguishable from their 24-track analog mastered brethren when played on contemporary digital gear, well, apart form a slightly flattened dynamics due to the limitations of 16-bit digital.

 The main reason why in the pro studio world recording engineers chose analog over digital is that analog overloads gracefully while digital – especially of the lower-spec 16-Bit variety – tend to be very unforgiving when it “hits the red”. And the low sampling rate produces digital nasties that even heavy metal rock musicians and their attendant mixing and mastering engineers exposed to almost constant 120 dB SPL’s of mayhem can hear, its no contest that analog wins even at the very tail end of the 20th Century. Given the proliferation of 24-Bit 192-KHz sampled “improved digital”, know of any heavy metal musicians mastering their works on 24-Bit 192-KHz digital? 

5 comments:

VaneSSa said...

The JVC DAS 90 Digital Recording System is only "lower spec" when compared to latter PCM digital audio recorders because it was released on the market earlier - i.e. it came first than the early 1990s Sony PCM-1610 - both of them use 3/4-inch U-Matic video cassettes to store an uncompressed digital audio data-stream. I think it was probably at the tail end of the 1970s when audio engineers found out that the high bandwidth of the then newly marked analog video recording cassettes could be used for recording linear digital audio bitstream.
A genuinely "earlier" digital recording system was Denon's early PCM recording that dates back from 1973 - a pulse code modulation system that samples digital music data at 44.1KHz at a 14-bit word rate. The early Denon PCM digital recording system stores the data in large open-reel tapes. These early Denon PCM 14-bit digital recordings from the early 1970s were later reissued on Redbook spec CDs during the 1990s.
Back to the JVC DAS 90 Digital Recording System - its specs rate it a 16-bit word-depth system whose sample rate is almost 50,000 Hz (as in the DAT / digital audio tape's 48KHz sampling rate?).

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exatlantean said...

According to the JVC DAS-900 brochure (JVC_900_Digital_Audio_System.pdf), the VP-900 ADC's sampling rate was 44.1 kHz, and I assume that the earlier ADC, the BP-90, also used this sampling rate. The JVC ADCs' superior sound quality was apparently due to their use of oversampling ADC units. According to a 12/13/80 Billboard article I found via Google Books, the JVC-90 was introduced at the 1980 Audio Engineering Society Convention in NYC. The BP-90 ADC alone cost $40K in 1980.

Also courtesy of Google Books, I found a DAS-90 ad in the 8/29/81 issue of Billboard, which in part reads as follows:

"JVC delivers the realism and quality that other systems merely promise. Most digital systems fall short of their theoretical benefits because analog input, filter, and output circuits are inadequate, degrading the recorded signal.
[...]
JVC's sound is crystal clear, with a solid stereo image, the result of quartz control, perfect phase integrity, DC to 20 kHz response (+/- 0.5 dB) and less than 0.02% total harmonic distortion."

The key phrases are "solid stereo image" and "perfect phase integrity," meaning that the DAS-90's anti-aliasing filters delayed all frequencies by the same amount of time through both channels, which is necessary to preserve the harmonic structure of the music and the timing-relationships between the channels.

The BP-90 ADC apparently used oversampling ADCs (a.k.a. sigma-delta ADCs or "1-bit" ADCs, where "1-bit" refers to the "DSD"-stage of the analog-to-DSD-to-digital process). I assume that these ADCs took the form of circuit boards in the BP-90. So, their ADCs would have had actual 16-bit linearity under all conditions and over the long term, and would have drastically simplified the requirements for their anti-aliasing (input) filters, allowing them to use simple passive filters with low distortion and a linear phase response in the audio range. JVC's system would have trounced Sony's in the early 80s, and not only Chesky CDs have had the potential for excellent sound quality since the dawn of the digital era.

Unfortunately, it would be another 25-30 years before the mass-market CD players in general could do justice to well-recorded CDs. Now, any reasonably-good new player or DAC has such good sound quality that CDs are the limiting factor, and not much of one at that. However, due to piracy concerns, the best-sounding versions of some albums are still put on LPs. So, if you absolutely must have the best version of some album, you're going to need a turntable. But at least turntable design has been refined to the point where you can get much better sound quality for your turntable-buck than in decades past. (For the best sound quality at the lowest price, get a belt-drive.) You should also get something to deep-clean your LPs, which doesn't have to cost a lot.

Notes

[1] Chesky had the ability to make 24-bit recordings which could be cleanly converted to CD-grade digital in the late 70's, but they apparently patented it and kept it to themselves.

exatlantean said...

I forgot to include the following in my previous comment:

For years, I've been trying to identify all of the commercially-available digital recorders that could have been used for making good-sounding 16/44.1 digital recordings at the dawn of the digital era.[1] Until recently, I was convinced that the earliest consisted of Sony's non-oversampling 16/44.1 decks with Apogee aftermarket input filters, the latter of which were introduced in about September 1985. But recently, in the course of performing research into the early Japanese Hendrix CDs, I discovered the JVC DAS-90 and DAS-900, which had excellent sound quality as far back as 1980, but which weren't as popular as the PCM-F1, perhaps due to the JVC gear's high price, or perhaps because a lot of copyright-holders didn't want to release master-quality digital recordings into the wild. But it bothers me that the DAS-90 didn't turn up in my earlier investigations into digital recorders. It's almost as if JVC's gear was being kept secret.

exatlantean said...

As usual, as soon as I post a comment based on some assumption, I learn that my assumption was incorrect shortly thereafter. In this case, my assumption was the BP-90 ADC had a 44.1 kHz sampling rate, but it apparently had a 50 kHz sampling rate, which in the early 80's couldn't be cleanly converted to 44.1 but apparently can be now. The VP-900 which was apparently introduced in 1982 did have a 44.1 kHz sampling rate. The 1984 CD-release of Weather Report's Heavy Weather (considered to be their best album, and which won some prestigious awards) is one of the few CD's I've ever heard with cymbals that actually sound like cymbals. Considering the release-date, I assume that it was digitized with a VP-900 ADC. (Another good one is Steely Dan's Alive in America, but it was recorded and mixed in analog for the best sound quality, and the output of the mixer was digitized directly with an Apogee AD-1000 20-bit oversampling ADC, which was introduced in 1993. The 20-bit data was converted to the CD-format with Apogee's UV-22 process.)