NOS (non-oversampling) DACs - Dan Lavry comments

this may be interesting for some of you, especially if you've not had the pleasure of suffering through years of EE study, Digital Signal Processing theory, and DAC design, or spent much time in the entertaining über-tech world of the AES......

those who have had such good times, know that in the world of dsp audio professionals, there is a very short list of people who truely understand the fundamentals and application of dsp, system design, analog and digital design, etc etc. -- and make products which prove it.

not hobbyists who "design" products; not "producer/composers who started recording" and spout drivel in online fora about dsp; not people who come from on-chip interconnect design and are stepping far outside of their expertise in pontificating about signal processing...

Dan's is one of the names often mentioned by the leaders in the field as someone who truely understands the technology of digital signal processing as applied in creation of pro audio products (as context, other highly-regarded names you may encounter in the world related to SH Fora are such as Daniel Weiss, without a doubt one of the gold-standard dsp guys; Bob Adams (Analog Devices, you owe it to yourself to read everything he's published about data conversion and sample-rate conversion); Jim "JJ" Johnston (one of the fathers of perceptual audio coding among many other signal processing achievements); Rich Cabot (tech brilliance behind the creation of Audio Precision and many other signal processing developments); Karlheinz Brandenburg, Harald Popp, Jurgen Herre and others at Fraunhofer; John Strawn, Mike Story, Bob Stuart...)

why the buildup about Dan?

simple: there is a lot of posting in audio fora about the alleged "superiority" of NOS DAC design. Generally, when you do some forensic investigation and track back through web postings, "reviews," references, etc; you find that the posters generally have little more than subjective info ("I like how it sounds") or anecdotal stories ("I've heard that..."; "my customers say..."; "this guy has posted a lot and says"); and as a rule few have any idea at all about the fundamentals of digital signal processing, sampled-data systems, analog and digital filter design, data conversion fundamentals, overall audio system design....

well, Dan is the real deal. He posts based in technology and fact. Any occasion when he makes time to post (especially in fora filled with die-hard subjectivists) and explain technology in a way to shortcut years of academic study, it's worth reading.

over in head-fi land right now, there's an interesting thread where Dan is taking pains (with some obvious frustration, he may be blunt but that is his nature) to explain the technology fundamentals underlying concerns about NOS design.

worth a read, enjoy:

http://www.head-fi.org/forums/f7/nos-dac-marketing-bs-438220/

 

Wow, I just read through the head-fi thread and don't envy Mr. Lavry a bit!

Although I don't currently own any of his products, I have had tremendous respect for his company as well as his engineering prowess for some time. It looks as if he took great pains to provide a significant amount of technical information (probably thousands of dollars worth if one considers that this is the type of information normally shared in engineering classes at universities), and to have (some) head-fier's dismiss it as essentially marketing copy is insulting. As soon as I'm done writing this I'm going to post over at head-fi thanking Mr. Lavry for taking the time to share his expertise; I just hope the negative (and sometimes outright disrespectful) posts don't permanently scare him away from this type of interaction in the future because manufacturer/designer participation is one of the best things about head-fi.

There is FAR too much voodoo and snake oil salesmanship in "high-end" audio as it is. I didn't think our hobby was in as much trouble as some hand-wringers have been leading us to believe, but when a respected engineer (indeed, one of the world's foremost authorities on digital audio) takes the time to provide an exceptionally well-written piece based upon quantifiable, reproducible engineering principles and is summarily dismissed as just another marketing guru protecting his interests, it's hard not to see the writing on the wall...

As to NOS DACs, I've never used one. I don't claim to be an engineer (just lowly B.S. degrees in Chem and Math and a non-engineering/non-scientific professional degree), but I am an electronics geek and have studied digital audio enough to understand that there is simply NO WAY a filterless DAC can even begin to approach the performance of a DAC which uses a properly-implemented digital filter. Mr. Lavry was attempting to convey this point using objective data, only to be shot-down by the "magical-thinking" folks. I understand that subjective considerations and psychoacoustics are part of the equation, but (IMO) it's all for naught if the underlying design is compromised from an engineering perspective. A NOS DAC might sound great to a particular set of ears, but from a quantitative engineering perspective is significantly flawed-this was the "take-home" point I think Mr. Lavry was making.

 

My NOS DAC experience is limited to a 'Monica 2' DAC kit that I built myself. It was very pleasant sounding though it lacked in detail. The high-end was very rolled-off which I imagine helps with harsher masterings.

My next digital project was a K&K RAKK DAC which uses a transformer coupled PCM1794. The filtering is built into the chip and has a host of other tricks. It soundly trounced the Monica DAC with just about better everything - imaging, detail, etc etc. However it was more revealing of the nastier side of bad masterings/recordings.

 

Haven't read his post (yet), but just wanted to quickly add this before the arguing starts: the analog output section of a standalone DAC, or the CD player or receiver, also has a lot to do with what one finally hears emanating from their speakers.

So comparing one type of digital conversion to another must take that into account.

 

oh, so you're one of those folk (like ChemE's) who spent their college years calculating all the equations behind the distillation column in your closet making booze?

yah, reading Dan's content first might actually be valuable...

 

I always enjoy reading Dan's posts...yeah, he can be blunt, but I like the no-nonsense approach, especially in an industry (on the consumer side, not the pro side) that can so easily fall into fantasy land. I hope to add some of Dan's gear to my stable in the future.

 

Lavry wrote: When I hear of no oversampling DAC, I think of the days when I designed such gear. I designed a DA at Analog Solution (the design was later adopted by Ultra Analog). I also designed the first Apogee DA (DA1000) and also some DA's for digital sound on film. All that was around 1990. That was before the over-sampling and up-sampling concepts.

That is not true as Philips' very first TDA1540-based CD players from 1982 employed 4x oversampling (to compensate for their 14-bit resolution). Philips employed oversampling in all their TDA15xx designs until they went the whole hog and switched to 1-bit BITSTREAM converters.

 

Whether or not *he* mentioned analog output sections would not have changed what I wrote in my post here. A person could take the best DAC chip ever made and connect its output to the preamp portion of a Montgomery Ward's $150 all-in-one system but the resulting music would still sound like poo.

 

oh, so you're one of those folk (like ChemE's) who spent their college years calculating all the equations behind the distillation column in your closet making booze?

He, he...
No, I plead innocent to any moonshining...
My preferred prankery mostly involved typical garden-variety pyro stuff (you can do some pretty interesting stuff with sodium peroxide for example ) and practical jokes involving liquid N2 and He (toss a liter of LN2 on the floor of a professor's office and hilarity ensues! ).