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John Curl's Blowtorch preamplifier part II
John Curl's Blowtorch preamplifier part II
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Old 8th August 2012, 01:27 AM   #25791
1audio is offline 1audio  United States
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John Curl's Blowtorch preamplifier part II
Frequency and time interval (period) are conjugate but frequency does not equal not all time. . .

With a single input and no reference what does phase mean?
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Old 8th August 2012, 02:15 AM   #25792
RNMarsh is offline RNMarsh  United States
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John Curl's Blowtorch preamplifier part II
Ok. Now we are getting somewhere close to what i have thrown out.... statisical studies of metadata has pointed the way to correlations and then real solutions in many fields.
Waveform shape cannot be seen on an FFt or THd et al. The phase, when known is not in a form that helps you get a quick take on its resulting sound qualitites.... yes you can make enough tests and reconstruct the original input but still need to know how sensitive the ear is to that waveform compared to other waveforms. etc etc etc.

On the other hand, -100db elements are not usually found in tube audio equipment. Thus, my stab at tubes... distortion and group-delay are sometimes severe enough to be able to hear.

Especially, if you look at the whole system from front to end... that might as well include the recording chain as well. What does the whole thing look like? Not one piece at a time connected to nothing else.

With waveform shapes as the hearing focus, for the moment, we are at a big disadvantage with FFT's that are not telling us anything about the shape... all by itself.

So what new test can better correlate with listening that we havent tried or can we make something new? At least for a few key waveforms that are sensitive ones related to hearing sensitivities. Maybe Dianna Deuche (sp?) can help us out with waveform selection.

Thx, RNMarsh

Last edited by RNMarsh; 8th August 2012 at 02:25 AM. Reason: Waveform shape and tests -
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Old 8th August 2012, 02:30 AM   #25793
SY is offline SY  United States
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John Curl's Blowtorch preamplifier part II
Quote:
Originally Posted by vacuphile View Post
In the case of music, what is the time domain function of Lou Reed's "Walk on the Wild side"?
It's a well-defined sequence of numbers that you can read off the CD. Same thing with a finite acquired noise sequence. One can transform between the domains practically to any arbitrary accuracy, depending on what your hardware and computing budget are.
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Old 8th August 2012, 02:43 AM   #25794
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Last edited by rcw666; 8th August 2012 at 02:55 AM. Reason: spelling
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Old 8th August 2012, 04:10 AM   #25795
ticknpop is offline ticknpop  Canada
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The bass in " Walk on the Wild Side " is unique. Herbie Flowers, the session bass player, played both an acoustic bass and electric bass track in the original multitracks. Unable to decide which they liked better, in the end it was decided to use both - so each bass note is played twice on an acoustic bass and an electric bass giving the bass an unusual sound on the track. Herbie was pleased, he got twice the usual 30 pound session fee.

Was there a meter, analyser, FFT, or other scientific marvel which would have told you that?

Spent an evening drinking with Lou Reed in the late 70's, he was abrasive and obnoxious, but aren't we all?

Last edited by ticknpop; 8th August 2012 at 04:35 AM.
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Old 8th August 2012, 04:40 AM   #25796
bcarso is offline bcarso  United States
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Originally Posted by ticknpop View Post
Spent an evening drinking with Lou Reed in the late 70's, he was abrasive and obnoxious, but aren't we all?
If given the chance.
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Old 8th August 2012, 06:21 AM   #25797
VladimirK is offline VladimirK  Uzbekistan
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Quote:
Originally Posted by vacuphile View Post
... Now, to the point. Take a realistic situation where you want to look at the distortion products of a 100 Hz tone. You need a window larger than 10 ms for that. That will capture at least two periods of the second harmonic. Now, asume that the second harmonic has the character of a pulse, with a high first period and a low second. What you will see on your screen is the average of the second harmonic, not the peak. The ear most likely is able to maintain resolution where the FFT is not capable of doing so.

This could be the explanation why two amps that measure identical can still have a different acoustic signature.

Anyways, there is theory and application, and I hope to have pointed out a shortcoming of FFT in its application for audio analysis. Important information gets lost. vac
There is no doubt in this conclusion, and I am just curious, why not to compare precisely the input and scaled output pulse wave forms?
Is there a rule approved by God precluding to make comparisons in time representation?

Last edited by VladimirK; 8th August 2012 at 06:26 AM.
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Old 8th August 2012, 06:33 AM   #25798
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Quote:
Originally Posted by vacuphile View Post
Now, to the point. Take a realistic situation where you want to look at the distortion products of a 100 Hz tone. You need a window larger than 10 ms for that.
A window length of precisely 10mS would do it rather nicely.

Quote:
That will capture at least two periods of the second harmonic. Now, asume that the second harmonic has the character of a pulse, with a high first period and a low second.
If we assume that then its no longer the second harmonic. The second harmonic is by definition a 200Hz sinewave in this instance.

Quote:
What you will see on your screen is the average of the second harmonic, not the peak.
Yes - DF96 has already pointed out that if you want to peer inside the window to see what's changing within the window time then probably wavelets are your best bet.
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Old 8th August 2012, 06:52 AM   #25799
Wavebourn is offline Wavebourn  United States
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John Curl's Blowtorch preamplifier part II
Here is the realistic picture.

I feed 400 Hz to the input and see on half power that 2'nd harmonic is -80 dB below fundamental, 3'rd harmonic is -135 dB, and the rest is invisible below noise level. Then I decrease level 10 dB and see that the 2'nd harmonic is below 100 dB, the rest is invisible. Increasing the level up to the maximum power I see the tail goes up, and at almost full power distortions are quite high, but when with decreased power they go down, their order gets lower, it is fine. It looks like high-end amp.
Then I feed mixed 1 KHz and 20 KHz and see how they intermodulate. Decrease first frequency gradually and see that at 40 Hz intermodulation is almost the same, below that it goes higher. I increase time constant of servo and see that intermodulation decreases. It is good. For even better result I would need better, more expensive output transformer, and now I can decide, do I want to go this road, or not.

FFT plots are useful tools, when used realistically. You have to remember that harmonics can not have character of pulses. They are steady sinewave parts of the complex signal. If you see on oscilloscope some pulse this pulse on Fourier plot is a mix of strictly sinewave harmonics.
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Old 8th August 2012, 07:05 AM   #25800
VladimirK is offline VladimirK  Uzbekistan
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Quote:
Originally Posted by Wavebourn View Post
Here is the realistic picture.....
No doubt, Anatoly, that this way you are able to adjust the amp at better reproduction of steady sine waves combinations.
However, it is not clear, do you improve single pulse reproduction by suppressing 40 Hz IM product, and what is a criterion for good pulse signal reproduction.
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