Sound Quality Vs. Measurements - Page 52 - diyAudio
Go Back   Home > Forums > Member Areas > The Lounge

The Lounge A place to talk about almost anything but politics and religion.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 3rd January 2012, 08:33 PM   #511
diyAudio Member
 
scott wurcer's Avatar
 
Join Date: Jan 2004
Location: cambridge ma
Quote:
Originally Posted by john curl View Post
First, you have to find a 'departure' from what you expect.
Your expectations were the problem.
__________________
"The question of who is right and who is wrong has seemed to me always too small to be worth a moment's thought, while the question of what is right and what is wrong has seemed all-important."
  Reply With Quote
Old 3rd January 2012, 09:13 PM   #512
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
JC's analysis in post 509 contains a big element of truth.

There is another way of looking at it, though. Someone with a misconception eventually realises it, and then assumes that everyone else has the same misconception so writes a book/article/thread announcing their amazing discovery. They are then disconcerted to discover some people never had that misconception so wonder what all the fuss is about. A variant of this is that the 'discovery' is actually wrong, but it rapidly displaces the actual truth in popularity for about a generation (5-10 years in audio?).

Last edited by DF96; 3rd January 2012 at 09:13 PM. Reason: typo
  Reply With Quote
Old 3rd January 2012, 09:15 PM   #513
jcx is offline jcx  United States
diyAudio Member
 
Join Date: Feb 2003
Location: ..
more like 30-40 yrs and still counting...

SS is harsh, negative feedback is bad, Otala "explains" why...

Last edited by jcx; 3rd January 2012 at 09:18 PM.
  Reply With Quote
Old 3rd January 2012, 09:16 PM   #514
diyAudio Member
 
Join Date: Feb 2009
Location: UK
Could I just return to an earlier part of the discussion which suggested that an amplifier that scores well in terms of THD may apparently sound poor because of transient distortion that may, or may not, be due to thermal effects..? The implication seemed to be that we must simply shrug our shoulders because there is no way to measure such an effect except perhaps to look for THD at such low frequencies that the chip has time to warm up and cool down (if thermal effects are the culprit) - and this doesn't seem to convince many people.

Could I ask why it is not possible to measure transient distortion directly in the time domain, rather than always looking for components in the frequency domain? I can see that in the past (pre-digital sampling and computers) THD was probably the only way, but surely nowadays it should be possible to see precisely why an amplifier supposedly sounds different from another by measuring the direct response to any transient signal we like. We can leave minutes between 'pulses' if we choose to, and take a single snapshot, or build up an average over hundreds of tests. There's a signal going in; there's a signal coming out (into a real load not just a resistor, hopefully - why do people only test amps on resistors?), so what's the difference between the two? Even if the result for a single amp is not as apparently directly meaningful as the usual 'proxy' for time domain distortion, THD, the difference between two amps (e.g. tube and solid state) would surely reveal something interesting.
  Reply With Quote
Old 3rd January 2012, 09:31 PM   #515
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
First, for an amplifier that doesn't have a delay line built into it (99.999% of amps used for hifi service), there is no difference between frequency domain and time domain- they are 1:1 inter-convertible. Even the time delay can be accounted for with the right type of signal transform, but it's a total non-issue for audio amps. Second, you can easily do time domain analysis if you wish- it's more convenient for some phenomena. There's a little-known instrument called an "oscilloscope" often used for these purposes. Third, you can sample and record outputs of amplifiers and see how they differ by subtracting one output from another- Bill Waslo's clever Diffmaker software is just the trick for that.

Fourth, of course, is that this "measures good/sounds bad" amplifier is a myth unless one excludes several basic measurements (usually for trolling or marketing purposes, sometimes both), or expects the amp to be an effects box when it's designed to merely amplify, or insists on judging the "sound" by means other than ears. The "low THD" thing is something of a red herring.
__________________
And while they may not be as strong as apes, don't lock eyes with 'em, don't do it. Puts 'em on edge. They might go into berzerker mode; come at you like a whirling dervish, all fists and elbows.
  Reply With Quote
Old 3rd January 2012, 09:35 PM   #516
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
The difficulty with interpreting time domain measurements is that simple non-distorting filters can make a big change to a waveform. You have to carefully subtract off all these effects by some minimisation technique and then hope that the residual is not too contaminated by minimisation errors. There seems to be a much clearer correlation between sound and frequency components than sound and waveform shape.
  Reply With Quote
Old 3rd January 2012, 09:53 PM   #517
diyAudio Member
 
Join Date: Feb 2009
Location: UK
Quote:
The difficulty with interpreting time domain measurements is that simple non-distorting filters can make a big change to a waveform. You have to carefully subtract off all these effects by some minimisation technique and then hope that the residual is not too contaminated by minimisation errors. There seems to be a much clearer correlation between sound and frequency components than sound and waveform shape.
@DF96

I was going to include a paragraph about mathematically nulling out designed-in factors like bandwidth-limiting, but thought it was over-complicating the question.

Your final sentence to me sounds like the circular argument I suspected: people are convinced that our ears work in the frequency domain (phase doesn't matter etc.) so even when considering transient effects, they always try to express signals in the frequency domain - even though the frequency domain is pretty meaningless for the transients that we think may be causing our amps problems. So we have a situation where an amplifier measures 'perfectly' for THD but apparently sounds bad, and there is no way forward except for listening to our 'golden' ears.
  Reply With Quote
Old 3rd January 2012, 10:15 PM   #518
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
Quote:
Originally Posted by CopperTop
Your final sentence to me sounds like the circular argument I suspected: people are convinced that our ears work in the frequency domain (phase doesn't matter etc.)
That is not what I said. There is experimental evidence that waveform shape is relatively unimportant when compared with frequency components. It is from this evidence that one might conclude that our ears work primarily in the frequency domain. Human ear physiology tends to confirm this. So we have experimental data on sound perception, and analysis of how the ear internals appear to work, and they seem to say the same thing. This does not mean that frequency is the whole picture, but it does appear to be much of the picture.
  Reply With Quote
Old 3rd January 2012, 10:32 PM   #519
diyAudio Member
 
Join Date: Feb 2009
Location: UK
@DF96

What is it that we suspect the amplifier is doing wrong with these transients? Isn't it something like 'pulling its punch' as the transistor heats up? e.g. changing hfe or some other parameters as it heats up during a single pizzicato violin note? It results in a continuously changing transfer function, where the change is dependent on the previous history of the signal. At any instant, if the transfer function of the transistor could be frozen, the distortion could be revealed very sensitively by feeding in a sine wave, but this is not possible. Edit: Other distorting mechanisms must surely be possible too, e.g. feedback causing instability and spurious clicks, ringing etc. that don't show up with steady sine waves.

Surely there must be some way of showing this distortion if it is real. Are you saying that it cannot be measured at all, or just that the time domain is not a good way to express it, even if it is the only way to acquire the data?

Last edited by CopperTop; 3rd January 2012 at 10:36 PM.
  Reply With Quote
Old 3rd January 2012, 10:37 PM   #520
tvrgeek is offline tvrgeek  United States
diyAudio Member
 
Join Date: Dec 2009
Location: Md
Yes, frequency and amplitude as each hair bundle seems to respond to a narrow set of frequencies, but wave shape as Nyqest tells us is-nothing but a sum of sine waves. What is even more fascinating is our evolutionary programming to know what is "correct" and what is not. I am not sure what advantage this had in history, but it wound seem to be the case. All this is terrible hard to measure because it is a soft science based on interpretation and statics. What our brain does with a few thousand sets of hairs is totally amazing.
More fun is what we do with phase, time delay, and the amplitude variations that our brain uses for localization and distance. A classic experiment is using very pure tones in a chamber to see how well we can localize. It turns out, in a horizontal plane, we can still localize. But in a vertical plane, we are totally lost.
Something I noticed in college, classic music students almost always had a speed control on their stereo's, but pretty crappy systems. My conclusion was that frequency accuracy was one of the clues for them what was "RIGHT". Where I could not tell if A was 440 or 442, as long as everyone played together.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Quality Control differences = variations in sound quality? KT Class D 3 4th June 2014 01:02 AM
Sound Card for Measurements Marik Solid State 2 2nd January 2012 09:59 PM
Sound Card Recommendations (For Audio Measurements) dchisholm Equipment & Tools 5 16th July 2011 10:40 AM
How to protect sound card during amp measurements? okapi Everything Else 13 2nd September 2008 04:06 PM
Sound cards - test and measurements jackinnj Everything Else 2 5th July 2003 04:02 PM


New To Site? Need Help?

All times are GMT. The time now is 09:44 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2