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Old 15th November 2009, 04:32 PM   #921
p-w is offline p-w
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John, I'm confused

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Originally Posted by MJL21193 View Post
That would be your expectation, why not give it a try? Different recording sessions using the same setup and amplifier will net visibly different results, let alone a completely different amp.
Surely only if the measurement system isn't very good (like a cheap soundcard) , if this is the case then the system is not capable of measuring small differences between amps, as its resolving power is smaller than the difference one is trying to measure.

What are you trying to show with the FFT? There are so many frequencies present that they each mask any distortion component of the others. All it seems to be showing is that the frequency response of the twos amps is very slightly different at low frequencies and identical above 80Hz or so.

Phil
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Old 15th November 2009, 05:08 PM   #922
Professor smith is offline Professor smith  United Kingdom
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One of the files which Nico uploaded was of course phase inverted. So theoretically if I match the levels and put one on top of the other there should be silence but I couldn't achieve this. I agree with Andrew that it's not a meaningful test, since there are many variables involved. When we start changing the levels digitally, this changes the signal.
Suppose we were to take a £10,000 cd player and a £100 cd player and phase inverted one and summed the two. I would bet you could achieve silence and this would show that small differences are being 'masked.' Either that or there is no difference. Actually could someone try this out?
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Old 15th November 2009, 06:19 PM   #923
AndrewT is offline AndrewT  Scotland
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the listening test is meaningful.
The comparison if done effectively may show why we hear the two samples as slightly different.
The idea that superimposing graphically two music samples and hoping to see differences due to tiny differences in distortion components is preposterous.

Had we the opportunity to pass the same mono signal through both amps simultaneously and with the outputs of opposite polarity, then we may have been able to record the difference sum. Who developed that test? Was it Baxandall?

I would be interested to see the three samples (amp1,amp2,diff), in sync, and see if, visually, we could see a trend of when the difference signal is not zero, eg on fast rising slopes or on high peak signals or???
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Old 15th November 2009, 06:24 PM   #924
MJL21193 is offline MJL21193  Canada
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Quote:
Originally Posted by p-w View Post
John, I'm confused

Surely only if the measurement system isn't very good (like a cheap soundcard) , if this is the case then the system is not capable of measuring small differences between amps, as its resolving power is smaller than the difference one is trying to measure.

What are you trying to show with the FFT? There are so many frequencies present that they each mask any distortion component of the others. All it seems to be showing is that the frequency response of the twos amps is very slightly different at low frequencies and identical above 80Hz or so.

Phil
First, what I have been showing (latest in post #919) is not an FFT, it's the frequency response of the entire file. I have mentioned this several times. It is a graphical representation of the sound file, showing the actual level for each frequency. It is difficult to explain and I took it for granted that everyone would understand what it is I'm showing. Anyone who has used a program like Audition will get it.
This is like a fingerprint of the amp and it's very difficult to get 2 to match so closely. Taking in consideration what I had to do to make these files the same level and phase (not to mention polarity) it's amazing they are as close as this.
Soundcard deficiencies are not an issue, the same soundcard was used to record both and the same is used to play them back. If anything, soundcard issues would cause a further rift in the data and make the files even more dissimilar.
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Old 15th November 2009, 07:34 PM   #925
p-w is offline p-w
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Quote:
Originally Posted by MJL21193 View Post
First, what I have been showing (latest in post #919) is not an FFT, it's the frequency response of the entire file. I have mentioned this several times. It is a graphical representation of the sound file, showing the actual level for each frequency. It is difficult to explain and I took it for granted that everyone would understand what it is I'm showing. Anyone who has used a program like Audition will get it.
I'm afraid I still don't get it. How is it different from taking the FFT of the file which gives the amplitude (and phase) for every frequency for the sample waveform?

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Soundcard deficiencies are not an issue, the same soundcard was used to record both and the same is used to play them back. If anything, soundcard issues would cause a further rift in the data and make the files even more dissimilar.
I was referring to your comment that you can measure the same thing twice and get different results, not commenting on the files nico had given us.

Anyway as Andrew said it is the listening that matters, lets just build the amp we like the sound of.

Phil
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Old 15th November 2009, 07:57 PM   #926
AKSA is offline AKSA  Australia
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Folks,

Let's hit this nonsense on the head. No more discussion of waveform analysis, it remains inconclusive, it is difficult to do, and ultimately it is corrupted by both low sampling rates and the horrific D/A converters in sound cards. Forget it, it's not effective and Nico was effectively saying this anyway with his haplesss attempt to give us all a listen.

Nico,

Thank you sincerely for the comprehensive input you have made, it has been considerable, above and beyond - not that you had any obligation to do anything. I sincerely hope you see fit to return to the thread, because your expertise is, to me and I'm sure to most others, indisputable. As a human being you are entitled to get your test clips the wrong way around - a simple enough mistake - and certainly not one to be pilloried about.

John,

Please leave this alone. The process has been flawed, chiefly because of the inaccuracies intrinsic in D to A conversion, and you have considerably upset Nico to the point where he is now leaving. You mention that as a man of science he should be amenable to criticism, fair comment, but you, as the critic, have an obligation to moderate the tone of your criticism so that it remains a discussion on objective, not emotive, terms. If you wish to prove yourself correct and Nico incorrect, please do it privately, not in a public forum. This issue has erupted as I have slept, and thus has gone unmoderated. No one here doubts you are smart, but you are brash, and need to pull your horns in. No one has all the answers, not even you, and attempts by any member of this forum to use the medium as a means of embarrassing others is both insidious and absurd.

No one is doing a service to this thread, regardless of technical input, if the entire discussion goes belly up and the principal technical player leaves because of unacceptable net etiquette. So please, give some thought to this and consider the consequences of the approach and tone you use. Correct people's errors by all means, but do it with grace and sensitivity. Realise that others have egos which must be managed, not confronted. I have been a member of DIYaudio since 2001, and I can number the truly disruptive individuals on the fingers of two hands. You are NOT one of those, but right now your behaviour has resulted in a huge eruption which is unwelcome, to say the least. And while I thank you for your technical input, I urge you to thwart your impulse to have the last word.

Folks,

This is a long, slow thead. Not much is happening fast. That is the nature of R&D and I make no excuses. The process is ongoing, piecemeal, and no one has built the final product at this point. Some excellent minds are working on the problem, and a solution will undoubtedly be found, but it will take time, and it is neither entertainment nor intellectual blood sport. Participate if you are sincere about helping and contributing in a mannerly way. Go elsewhere if your intentions are to show up others, or openly condemn. I have enjoyed private email and phone conversations with Nico Ras for some months, and know him to be an extraordinarily competent, loyal and worthy individual. Playing the man always ends in tears, and I'm furious about this.

I don't care what is said in objective terms about the technology, but any comment made about personalities is off limits and will be edited out in future. Please, cooperate, otherwise continuing evolution of the amp and survival of this thread will be threatened.

Hugh
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Old 15th November 2009, 08:22 PM   #927
MJL21193 is offline MJL21193  Canada
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No problem Hugh, I'll leave you men to it.
You picked the one that sounded best and that's the way to go.
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Old 15th November 2009, 08:33 PM   #928
AKSA is offline AKSA  Australia
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John,

Thank you for your measured response and acceptance of my criticism, much appreciated. I hope you continue to contribute, I really do, as you have great technical ability. I don't mean to single you or anyone else out, not my style, but neither do I resile from my comments. I am trying to keep this thread pleasant and informative, without confrontation. With smart people, that is always a challenge,

Cheers,

Hugh
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Old 15th November 2009, 09:05 PM   #929
MJL21193 is offline MJL21193  Canada
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Hugh,
Like I said, no problem. I have a pretty thick skin and the weight of criticism is always relative to the source - my ego is intact!

As for contribution, I'll probably follow my first instincts (from many days past) and stay away. My help thus far has been negligible - you probably won't miss it.
Goodluck! and goodbye.
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Old 15th November 2009, 09:54 PM   #930
keantoken is offline keantoken  United States
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This is making me curious, now I'm gonna have my own listen.

John, could you Email me those files?

- keantoken
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