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MQA and the "Pre Ring - Post Ring" Hoax

There's been a lot of misinformed babble on various audio forums about impulse response, digital filters, "time errors", "time correction", "time blurring", and similar pseudo science clap trap to convince audiophiles that suddenly in the year 2018, there's something drastically wrong with digital PCM audio - some 45 years after this landmark technology was developed by Philips Electronics engineers. Newsflash folks - it's a scam.

First, let's take a close look at what an impulse or discontinuity signal really is. The wikipedia definition actually is pretty accurate thanks to a variety of informed contributors from around the globe. It is a infinite aperiodic summation of sinusoidal waves combined to produce what looks like a spike (typically voltage for our purposes) in a signal. Does such a thing ever occur in nature or more importantly in our case - music? Absolutely not. In fact, the only things close to it are the voltage spikes that occur when a switch contact is thrown or an amplifier output stage clips because supply voltage to reproduce the incoming signal waveform has been exceeded. So if this freak of nature signal representation doesn't exist in nature or music, of what good is it in measuring the accuracy of audio equipment? The answer might surprise you.

In fact, impulse response, or an audio system's response to an impulse signal, is one of the most useful and accurate representations in existence of such a system's linearity and precision - or its fidelity to an original signal that is fed to it.  A lot of  focus has been placed on the pre and post ringing of these "discontinuity signals"  but what you have to understand is that the ripple artifacts are nothing more than an analog system's (all electronics is analog -digital is just a special subset of analog) limitation in attempting to construct the impulse or discontinuity signal waveform. They are a result of the impact produced by the energy storage devices themselves in creating the signal. To create a large energy peak, you need large storage devices. The larget the capacitor for example, the longer in time it takes for it to absorb and discharge electric field energy. This is the same with inductors. One type stores electric field energy - the other magnetic. Smaller value capacitors can react to voltage changes very quickly but are limited in the peak value of energy that can be stored and dissipated. But if you combine a large number of high value and low value devices in a circuit and apply a voltage spike, you wind up with the kind of oscillations you see in an impulse response graph. Small capacitors for example, rapidly reach their charge capacity and can discharge into larger capacitors that are much more slowly building up charge in the transition from no input voltage to full spike value. This "sloshing around", if you will, or oscillation is what happens in circuits built to provide extreme voltage attenuations. In a linear, time invariant system, any rapid change in frequency response or time response - has these characteristics.
So effectively the entire debate about ringing in digital audio is a misnomer - a hoax. The impulse response ripple is not something that happens in real world sounds or in a properly designed audio reproduction chain. Ever since digital oversampling was developed in consumer products in the early 1980s, there has been no need for steep analog filter circuits with their attendant ringing. The problem very simply DOES NOT EXIST. The ringing generated  artificially in an impulse signal is useful in that it provides a very high frequency stimulus to linear audio systems as  a means of measuring high frequency and transient response. IT IN NO WAY BY ITSELF, REPRESENTS THE TIME DOMAIN BEHAVIOR OF THE AUDIO REPRODUCTION CHAIN. An accurate audio reproduction system should fully render the impulse signal in all its pre and post ring glory without alteration. Any audio system that eliminates or significantly alters this pre/post ringing present in the signal that is fed to it is not truly "high fidelity" and is thus bandwidth limited.
cj1965
cj1965 OP
124 posts
 
@tomcy6

I'm very calm. Use of capitals doesn't mean I'm not very calm. I'm not sure how to highlight or boldface anything for emphasis using this interface. Unlike most of the participants here, I don't bother posting to such forums very often. I just don't have the time to amass 5 or 6 thousands posts on an audio forum so I'm a little green when it comes to finding features like emojis or text editing buttons.

As for anger or hostility towards others - if someone pops into this or any other thread with an insulting comment like:

you're a "truther" spreading propaganda - without anything to back up this statement or factually contradict anything presented in the thread, they will be responded to in kind (see above comment from rbstehno). Essentially all of that users comment was personal attack and nothing was focused on the actual information presented in this thread which centers around ignorance of what a Dirac Delta or Impulse function really is. Whether or not you or others have thin skin and don't like it when someone points out the complete lack of knowledge or understanding on the part of members talking about "pre ring" - I can't help that. The facts are what they are. Impulse signals are what they are - special signals that have absolutely nothing to do with what audio circuitry deals with on a regular basis.

All forums such as this strongly encourage participants to focus on the subject matter and avoid attacking the messengers. Just because you don't like the message, it doesn't give you or rbstehno the right  to personally attack another member's character with unsubstantiated "truther" or "propagandist" labels.
czarivey
4,494 posts
 
MQA and MP3 have near same level of signal loss.
I did A/B with 24/96 vinyl rip.
MQA is just as lossless as MP3.

tomcy6's avatar
tomcy6
1,368 posts
 
Your point that preringing and postringing do not exist is not generally accepted as fact among the people who design and build audio equipment.  If you want to present that opinion to us, fine, but to say it's fact and that anyone who doesn't agree is ignorant is not helpful to your cause.  I'm just suggesting that you lower the intensity of your posts a little.  We don't need an MQA war here.  As I said, there are forums where such a war would be welcome.


uberwaltz's avatar
uberwaltz
4,946 posts
 
OP
You made some very good salient and interesting points that had me reading deeper.
BUT( sorry could not resist)
The use of caps to "shout" and your general "take no prisoners" attitude will not win you any favours here. Members will unfortunately soon look past the meat of this thread and just concentrate on the flesh (insults, attitude, shouting etc)
That will not help your cause of the one of this thread one little bit and that would be a shame.
It is hard I know when one feels they are being personally attacked but may I suggest a modicum of patience?
cj1965 OP
124 posts
 
" Your point that preringing and postringing do not exist is not generally accepted as fact among the people who design and build audio equipment. If you want to present that opinion to us, fine, but to say it's fact and that anyone who doesn't agree is ignorant is not helpful to your cause. I'm just suggesting that you lower the intensity of your posts a little. We don't need an MQA war here. As I said, there are forums where such a war would be welcome." -  tomcy6

Please cite some examples of "people who design and build audio equipment" who claim that music reproduction involves "pre and post ring" signals. I use impulse tests on a daily basis. I would like to see evidence of ultra broad band high intensity, ultra short duration peaks in music or any other signal source to back up what you appear to be saying. If you read the thread carefully, you will find that no one is saying pre and post impulse ripple doesn't exist. What you will find if you actually read the beginning of the thread is that these phenomenon only exist in circuits that utilize extreme attenuation of signals. Filter theory is very old. There are no special new filters that violate the laws of physics. Every steep filter produces oscillations that can easily be calculated for mathematically in the transfer function and represented in a Bode plot displaying stability or lack thereof. The problem with the entire foolish MQA promotional exercise is that a handful of "Industry people" are using impulse response data to infer that such signals are routinely present in music and their special characteristics (pre/post ripple) must somehow be dealt with. This is a complete farce that exposes widespread ignorance in the "audiophile" community - or at least that subset of the community that embraces ridiculous postulations about impulse signals that aren't true for the majority of music data fed to digital circuits.

Again, if you know anyone in the industry who can demonstrate that pre and post impulse ripple is encountered in music playback, I for one would like to see evidence of it. The anecdotal " I know some people" isn't sufficient. Evidence is required. If you want further citations for what an impulse signal is, I can provide links and you can actually generate them yourself using readily available software and a modest equipment setup. You can contrast the signals you produce with that of sharp pulses produced by a square wave generator - another signal type that doesn't exist in the real world of music but is used for equipment testing nonetheless.

There's an old saying about "a little information" being dangerous. That is precisely what is going on with MQA and signal ringing. The folks that are being misguided know just enough about the subject matter with which to make fools of themselves. Take the time to at least generate some impulse response signals yourself before you go on an internet forum to "educate" others about it. I have done it. You can too.
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