Dr. AIX's POSTS — 19 December 2013

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Marketing gurus love big numbers. I’m sure some psychologist could tell you why humans gravitate to ever-higher numbers but my guess says that we’re just wired to appreciate larger values. Of course, we want faster cars, more pixels, bigger bank accounts and more free time. But on the other hand…we want less girth around our midsections, lower times for the 5 or 10K races that some of us run and fewer taxes, right?

So I’ve always been amused when I see larger and larger numbers in the audiophile marketplace. We’re all familiar with the gradual move from 44.1/48 kHz sampling rates and 16-bit word lengths to 88.2/96 kHz and 24-bit PCM specifications. The ubiquitous Pro Tools digital audio workstation blasted right past those numbers and put out it “HD” system a number of years ago. The I/O units were actually called 192s because they could run at 192 kHz. No matter that virtually no one was operating at that level because none of the plugins were able to keep up and the computer power was too anemic to run more than one at a time. It just felt good to know that is was capable of 192 kHz.

There is ample justification for higher sample rates and longer word lengths to a point…at least for PCM encoded audio. But can anyone justify a “35-bit 844 kHz” DAC and Digital Preamp? I don’t even know how they got those numbers. The product is real and made by NAD…a company whose products I have owned and enjoyed. It’s been a while since I had one of their early preamps but I always appreciated the simplicity and sonic purity of their designs.

The M51 doesn’t sound like they’ve continued with the “simple is better” philosophy of their earlier models. Here’s how they describe the operation of the unit:

“NAD’s technology uses a very powerful processing engine that operates at much higher speed and with much greater accuracy than typical Digital-to-Analogue converters. Running at 108MHz, the M51 resamples the incoming pulse code modulated (PCM) signal and converts it to a pulse width modulation signal (PWM) with a sampling rate of 844kHz. Operating in a differential mode with double precision, the M51 has state-of-the-art specifications for low noise and freedom from distortion. The extreme headroom afforded by the 35-bit architecture allows for a DSP-based volume control that does not reduce resolution. Even with 24-bit high definition signals, the output can be attenuated by 66dB (very, very quiet) before bit truncation begins.”

The above description sounds really promising, but remember it was written by the marketing department and not by the technical people at NAD. What they are saying is that they believe they can improve on the quality of the output signal but transforming the digital input stream into an completely different data representation (the Pulse Width Modulation) at a very high sampling rate AND using longer word lengths. They also put tremendous emphasis on the ability to attenuate a digital signal in the digital domain. I don’t buy any of it.

If the incoming PCM digital signal is already pristine, highly dynamic (using perhaps 20 bits of the available bits…and that would be a lot!) and properly clocked, then recasting it as a PWM signal at 844 kHz with 35-bits wouldn’t “improve” the sound at all. It might change it…but if it were already as clean as it could get, then mucking around with it in this manner wouldn’t help. It couldn’t because the dynamic range, frequency response and all of the other specifications have already eclipsed the ability of humans to perceive any additional enhancement.

What could you do to improve distilled water with some sort of filtering or modifier…nothing. Same idea.

Just think about the 35-bit specification for starters. As a computer guy (MS in Computer Science CSUN 1992), I can’t figure out how or why they thought to use 35-bits. There’s a reason why bit lengths have always been powers of 2 (the binary language of digital computers or multiples of 8. We’ve had 8, 16, 24 and now 32 bits…but 35? This is a fell good number as is 32-bits. The dynamic range of human hearing is not much greater than 130 dB SPL. AND 24-bits gives us the potential for 144 dB, so why bother. Also keep in mind that most recorded music doesn’t reach even 10-bits of dynamic range.

The conversion to 844 kHz PWM is bogus too. The knowledge that skilled designers have about PCM is very thorough and deep. Current designs like the Benchmark DAC2 reach well beyond the sonic realities of the recordings that we’re buying. So why mess about with PWM and bigger numbers? Because it gives the marketing people, the reviewers and addicted audiophile consumers something to talk about.

Bigger…at least in this case…is most definitely not better.

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About Author

Dr. AIX

Mark Waldrep, aka Dr. AIX, has been producing and engineering music for over 40 years. He learned electronics as a teenager from his HAM radio father while learning to play the guitar. Mark received the first doctorate in music composition from UCLA in 1986 for a "binaural" electronic music composition. Other advanced degrees include an MS in computer science, an MFA/MA in music, BM in music and a BA in art. As an engineer and producer, Mark has worked on projects for the Rolling Stones, 311, Tool, KISS, Blink 182, Blues Traveler, Britney Spears, the San Francisco Symphony, The Dover Quartet, Willie Nelson, Paul Williams, The Allman Brothers, Bad Company and many more. Dr. Waldrep has been an innovator when it comes to multimedia and music. He created the first enhanced CDs in the 90s, the first DVD-Videos released in the U.S., the first web-connected DVD, the first DVD-Audio title, the first music Blu-ray disc and the first 3D Music Album. Additionally, he launched the first High Definition Music Download site in 2007 called iTrax.com. A frequency speaker at audio events, author of numerous articles, Dr. Waldrep is currently writing a book on the production and reproduction of high-end music called, "High-End Audio: A Practical Guide to Production and Playback". The book should be completed in the fall of 2013.

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