Better metrics for audible distortion?

Thanks very much for moving this here.



I understand your concern, and I agree completely with the desire to spend as little as possible to obtain a desired level of performance. But I think the Geddes/Lee approach is overly complicated and doesn't really solve that problem. Though I'd love to hear from ArnyK if he has time to comment.

To my way of thinking, distortion and aliasing, and even noise, all fall under the concept of artifacts. Regardless of the cause or source, what affects artifact audibility is 1) relative volume compared to the original source, the overall volume (SPL), and the masking effect. My Artifact Audibility article is similar to the tests in my AES Audio Myths video, and it lets people hear for themselves how loud a nasty sounding and highly obvious artifact must be in order to hear it. As these demo files show, once you get much softer than -60 dB or so, artifacts are inaudible regardless of their absolute volume and masking. Adding an extra 20 dB safety for "golden" ears, that tells me that an IMD measurement of 0.01 percent is a safe guarantee of the device in question not harming audio quality by a noticeable amount.



Sure, and I'm the first to claim that detailed math is not needed for most things related to understanding audio. As part of my audio test device I'm currently developing, I need to design four-pole filters and related circuits, but even that isn't nearly as taxing as the math I saw in the Geddes/Lee papers!



I tend to doubt that. It's easy to make high quality transparent audio devices, and any company that knows what they're doing makes good stuff and has no need to obfuscate or be dishonest. Yes, there are plenty of lame companies, mostly in the boutique hi-fi world, but those companies - and their customers - don't believe in specs anyway. Why else would someone pay $3,000 for a 6-foot piece of wire that's demonstrably identical to a wire costing $3 at any hardware store.

--Ethan

Geddes and Lee happen to be long term friends that I see socially several times a year. We know each other's kids, for example.

The first thing to consider is that Earl is primarily interested in speakers and his first cut on the performance of electronics gear is that it is usually perfect for all practical purposes. His systems are usually based on mi-priced receivers, and one of his hard-to-argue-with assertions is that if your speakers are efficient like most if his, you don't need more in the way of electronics but mid-fi digital players and amps (receivers).

So, trying to use Gedde's ideas and papers to argue that electronic gear has audible distortions that don't show up in traditional measurements completely misses his point and perverts his ideas.

His assertion is that it will be along time before we have speakers that are as subjectively ideal or as good as inexpensive electronics gear, and so we need to have distortion measurements that allow us to predict subjective performance and rank electroacoustic products like speakers effectively.

I agree that there are giant holes in the usual interpretation of THD and IM distortion when they are audible, but its easy to determine experimentally that outsize of clipping and the like, good average audio gear is free of audible distortion. Most electronic audio gear THD and IM specs are to me just fancy and possible overly-complex ways way to say "No audible distortion - fuhgeddaboutit"

From the following:



The first problem with what's written above is that its perfectly general to all audio gear and stated with no limits or qualifications. Geddes papers generally only apply to speakers.

Secondly, some actual study of the paper's titles seems to be in order. They are: "Auditory Perception of Nonlinear Distortion..."

The papers are talking about Nonlinear Distortion which is one of the three traditional kinds of measured faults that audio gear can possibly have. The problem are not the measurements, but how they are interpreted. Geddes calls the ways they are interpreted Metrics.

The three kinds of measurable faults in audio gear are:

(1) Linear Distortion which includes things like frequency response amplitude and timing errors like phase shift.

(2) Nonlinear Distortion which includes things like THD, IM, FM Distortion and Jitter.

(3) Interfering Signals which includes tics, pops, hiss, hum, and EMI.

Everything we don't like about how audio sounds to us fits into these three categories. Mathematically, there can be no other errors.

Wow and flutter are two names for similar kinds of nonlinear distortion.


They are both FM distortion.


Wow is what you get when the frequency modulating frequency is very low, and flutter is what you get when the frequency modulating frequency is a little higher.  


They are also kinds of jitter which is FM distortion.

I am attempting to correct your understanding of the Geddes papers



To make the point of how incomplete your understanding of the focus of the papers is.



I'm trying to get you to understand that "the cheapest equipment (or just speakers if you really want to restrict it to that) that has no audible distortion" is not the context or purpose of the papers.



It might be easier for you to understand what I'm talking about if you opened your mind to what the Geddes papers are actually about.