Sunday, April 20, 2014

Visualize…Sound

Hello folks,

A mastering engineer buddy from Albuquerque sent me a note about Ruben’s Tubes, a gadget for visualizing wave theory. We’re all geeky at the ASM, so I thought I’d pass it along…

Imaging a Helmholtz resonator, a.k.a. organ pipe. Then imaging busting out your trusty hand drill or drill press, and creating an in–line series of holes down the entire length of the pipe. VoilĂ ! You have a Ruben’s Tube, named after the entertainer and humanitarian, Paul Reubens. Kidding, just kidding.
Anyway, by attaching a speaker to one end of the tube and a regulated source of flammable gas say, clean burning propane, you have a Mad Scientist physics experiment in the making. Bwahh hah hah!
OK, enough already. Why all this yammering? You’ll see, just watch. Here are some links:


  • https://www.youtube.com/watch?v=HpovwbPGEoo
  • https://www.youtube.com/watch?v=ynqzeIYA7Iw
  • https://www.youtube.com/watch?v=jLNhRe24wm4
  • https://www.youtube.com/watch?v=2awbKQ2DLRE
Enjoy and, Happy Easter!

Saturday, April 19, 2014

An Ode To Engineering

Some things just aren’t right. Take, for instance, canned peas. Someone should really put a stop to that. (Frozen ones are another thing altogether...) You know what’s another evil that simply will not go away? Lying with numbers. OK, stretching “the truth,” with numbers. Now we all know that a sufficiently motivated person can make any statistic look good to the uninformed. Even I, dear reader, has been known to inflate concepts a bit. All for the greater good, I assure you…

But, here’s what I’m talking about: Most all the new electronic gear, audio and otherwise, that you find in the marketplace is digital, with analog mostly relegated to the vintage or boutique buyer. From entry level gear with an (IEC 60958 Type II) optical input to the stuff sporting a BNC spigot and hefty price tag, its digital. And never has there been so much hype made from so little.

Let’s suppose that you’re in the market for some new equipment. Who isn’t, after all, always lusting after the shiny and new. Or, let’s say that you want to become more informed about your chosen avocation. Of course, the audiophile industry has it’s own reality distortion field whereby most so called designers have never actually designed the guts of a single product in their entire life.

Anyway, lots of products at Costco are sold as “x bits” or such and such a sample rate but that really doesn’t tell you much. The truth is, as always, not black and white but numerous shades of gray. In general, all digital gear has the same basic advantages; good multigenerational noise and distortion performance with high amplitude signal, theoretically perfect archival longevity, an ever increasing price/performance ratio, and the ability to deliver the literal master recording directly to the consumer. For now, let’s look at the first and last distinctive attributes, the ones fundamentally different from analog…that “perfect sound forever” thing.

A device that has a 24 bit I/O can be advertised as a 24 bit product. That’s because the AES/EBU standard, including the aforementioned IEC 60958, is defined as having a 24 bit payload or essence. Needless to say, the I/O word length has nothing to do with what happens to the data once its inside the box. Sloppy implementation often leads to 18 or 20 significant bits and the AES/EBU output would still be a “24 bit” output. Only the first 18 most significant bits would carry any useful information though. And my, how nasty it would sound.

Sample rate specs are also suspect, though less so. All things being equal, a product that operates at 96 kHz should have wider unity gain bandwidth than that same product operating at 48 kHz. Well, so what? I certainly can’t hear a sine wave above 20 kHz! But is that all there is to our sense of hearing? I can’t say with authority that the increased bandwidth alone “sounds better,” but I can say that my ears tell me a well designed piece of gear sounds better operating at 176. 4 kHz than it does at 44.1 k. There’s obvious theory that shows it should exhibit less group delay or temporal distortion when operating at higher sample rates but no one knows the “true” reason or even if the “sounds better” effect is statistically significant.

The flip side of higher sample rates is the need to really nail the jitter performance. To be more specific, to control jitter immunity, which is particularly egregious with USB and optical inputs…more on jitter in a moment.

OK, how about word length? That parameter is, in some ways, more obvious and yet more obscure. Our hearing has, on a good day, about 120 decibels (dB) or 20 bits worth dynamic range. In the past, we’ve gotten along just fine with analog tape or vinyl that had, if it was lucky, half that dynamic range. Of course, double ended noise reduction addressed that shortcoming but the fundamental question remains: Why do we need 144 dB of dynamic range in the AES essence if we can only hear 120?

It’s those doggone numbers. A minimalist recording whereby a low noise analog source feeds a high quality converter and that performance is released, unedited, to the consumer wouldn’t need more than 16 bits to convey the information reasonably. But, most music isn’t produced that simply. Even classical releases, those pristine records of acoustic events, are usually edited so aggressively that one, two or three thousand edits in an hour long performance is not unusual. So? In the digital world, almost any process performed on the data, whether it be editing, EQ, gain changes or mixing, results in longer word length data that what you stared with…6 x 6 = 36. A one digit number times a one digit number equals a two digit number. Same with AES data. You make your 16 bit recording 1 dB louder and boom, you’ve got some extra low order bits filled with leftover or “remainder,” as my grade school math teacher called it. You need extra “headroom,” many extra bits, to store all that leftover from the multiplication used in modern digital music production.

And that’s not all. Noise is usually spec’d as an absolute noise voltage or indirectly as a signal–to–noise ratio. Very rarely are specs released that talk about the nature of the noise: it’s spectral makeup, it’s amplitude graphed against frequency, or whether it’s correlated with the signal or not. That last one can be particularly annoying and comes into sharp focus when lossy codecs, such AAC or mp3, are in da house. Our ear/brain combination is really good at noticing correlated noise and distortion, where the bad stuff bears some resemblance to the good stuff.

Phase response, harmonic and IM distortion, these are also important gauges of how the device will perform but do not directly predict how it will subjectively “sound” unless the performance borders on pathological. On the other hand, that blanket statement isn’t true for jitter. Though most manufacturers fail to state anything about their product’s jitter performance. Again, it probably wouldn’t say much about the sound since, like noise, there are so many aspects of jitter behavior. In general, jitter effects the subjective quality of multichannel audio as it heavily impacts the frequency vs. phase response, which in turn affects imaging and soundstage. Alas, few pop music engineers care about such trivialities as soundstage and are content with their pan pot synthesized, flat as a pancake, two dimensional world. So too are most consumers, but you’re not one of those, right?

Oops, I wander from the subject at hand…And that subject is simply this: Don’t believe sales and marketing hype, good or bad. Start learning about the underlying technology to which you listen every day. The laws of physics have not been repealed just yet. Of course, if you’re the sort to buy a new car solely on it’s looks alone, then put the magazine down now and move away from the toilet. For most of us, however, purchasing new big ticket items often means careful deliberation rather than impulse buying. Usually we have to live with our purchases for quite a while. If you don’t possess the expertise or aural acuity required to evaluate some box properly, then ask or rent someone who does. Ya just might learn something!

Monday, March 12, 2012

Wednesday, January 25, 2012

Bring and Brag, ASM Get Togather

Here are a few pictures from our January get together.

Our President opening the meeting







Club Treasurer Giving his CES report.




Gracious board member donating an OPPO for club use.

Presenting on annual donation to the Pavek

Wednesday, March 23, 2011

High Emotion meeting


Mike Shields Principal Designer





















Tuesday, November 9, 2010

ASM Fall Meetings September and October

September, Paul Bolin spoke to the group.


October, John Wolff of Classic Audio Loudspeakers.









We also had a F5 Building Sub Meeting prior to the normal meeting.

Tuesday, June 1, 2010

ASM Speaker Project

Here are a few pictures from the event. A full writeup to follow including cabinet drawings crossover and measurements.