Here is an article on how much distortion we can hear and also about how much phase shift. I am not sure about the phase shift article but although the article about distortion is from 1957 ( my age ) nothing much new has being learned about that in the mean time i am afraid.
The Wireless World Archive
The Wireless World Archive
Joachim, this is quite interesting. The closest to this I have ever come is the ISO34 multi-tone stimulus which is part of the AP software package. As the name says, this is a 34-frequency multitone. The frequencies are spaced such that the harmonics and the IM products all fall between the stimulus spectral lines. So, what you do is remove the spectral lines of the original signal from the output signal and what is left are the HD and IM products of the complex stimulus. It is then just a matter of number crunching to unravel the the various products. In fact, you can even measure the freq response by looking at the response to the original signal, and even measure the noise in the presence of signal by looking in the fft frequency bins where there is no signal!
But, this is limited to 'only' 34 frequncies at a time, and I would expect the pseudo-random signal you mentioned to be even more complex than that.
Whether that gives even more information about the performance of the DUT is a question - with the waterfall you showed, I think it is not easy to draw conclusions of what is good or bad of the DUT, and how to make it better!
jan didden
Joachim,
Noiseloading. Cool.
I have been preaching this for decades, we used it in the 80's in east germany, but without FFT and such, Just switchable calibrated bandstop/pass filters, 'scope and AC mV Meter...
Ciao T
Noiseloading. Cool.
I have been preaching this for decades, we used it in the 80's in east germany, but without FFT and such, Just switchable calibrated bandstop/pass filters, 'scope and AC mV Meter...
Ciao T
Jan,
See the first picture... Noiseloading.
It can be also (with difficulty) done using an AP2...
Noise with a deep notch (or several). Measure how much the signal "notch" fills in with DUT.
I once proposed this test to a famous (UK based) designer working for a famous audio company as a way to see what really goes on.
He found that his "24 Bit DAC" measured < 60dB dynamic range this way...
Ciao T
See the first picture... Noiseloading.
It can be also (with difficulty) done using an AP2...
Noise with a deep notch (or several). Measure how much the signal "notch" fills in with DUT.
I once proposed this test to a famous (UK based) designer working for a famous audio company as a way to see what really goes on.
He found that his "24 Bit DAC" measured < 60dB dynamic range this way...
Ciao T
Joachim,
I completely agree with you.
As I said, I'm a simple diyer, I'm not a professional nor a researcher. I looked for available instruments that allowed me to better correlate what I heard with what I measured. I don't pretend and don't want any paternity about this type of measurement: I used it to measure the transient response of a circuit. Up today, this pulse allowed me only to "clone" the sonic DNA of a good sounding (in my system) audio device. More than any other type of measurement; this is my limit.
I agree with you about the superiority of analogue instrument in this field (or, at least of affordable, for my resources, digital systems): in fact, I still prefer to use an HP8116A pulse generator and a Tek 5115 scope. The digital technology, on the contrary, has the advantage of better storage and numerical post processing.
About the pulse shaping according to a reference, I found that the job it's not so simple how the theory would suggest, because the parasitics of the circuit and the active devices, all than linear, work against this task.
By the way, according to my knowledge, this is one of the main reason of the superiority of tubes: the parasitics of the tubes are more linear than in solid state devices.
Ivigone and VK, I commend both of you, especially, because you have shown a strong sensitivity to what I have found in my own design work. I consider the effect of just about everything, from power supplies, wiring, circuit thru-path, etc., etc. It is the only way to succeed in making a 'world class' product. The real competition out there, does the same thing.
For everyone else, be not too sure about your complete understanding of phase distortion. There is more evidence out there from Bell Labs, etc., than is commonly published.
For everyone else, be not too sure about your complete understanding of phase distortion. There is more evidence out there from Bell Labs, etc., than is commonly published.
Can you give an example of an amp with flat frequency response that has phase distortion?
Hi,
You should have tried to listen to them...
Ciao T
PS, in principle you could use a snare rimshot or full hit as signal for impulse testing, you just need to record the signal played at sufficient resolution and sample rate, overlay the original and re-recording, invert the polarity of one signal and then subtract. What remains is "distortion".
Interesting stuff. I naively tired to do impulse testing with "real" signals. Single hit of a kick drum, snare drum, single note of a cello, etc. They only thing I learned is that I could not tell what was going on.
You should have tried to listen to them...
Ciao T
PS, in principle you could use a snare rimshot or full hit as signal for impulse testing, you just need to record the signal played at sufficient resolution and sample rate, overlay the original and re-recording, invert the polarity of one signal and then subtract. What remains is "distortion".
Multi-tone Testing
I may have missed additional comments on this topic, but a critical aspect of multi-tone testing is whether the tones are phase correlated or not. Once upon a mass tape replication system ago I used a multi-tone signal to check frequency response, and when the tones were digitally synthesized and locked in phase to each other the actual peak levels were far lower (20dB or more in some cases IIRC) than when the test signal was generated by summing 12 multiple free-running analog oscillators. In order to more accurately model compression we used the analog-generated version. Somewhere I have a RDAT with the two compared, and it is remarkable! (thus accounting for my remarks, I guess...).
The remarkable thing we deduced from the tests was at some high record level there were transient holes in the frequency response with distortion peaks depending on the exact delta-v delta-t at each instant; we assumed it was due to slew limitations in the record system. That is to say, in the presence of aligned wavefronts, headroom would be used up on a transient basis, causing odd distortion component generation. We could not catch all of those transient distortion components to see if they were harmonically related to the test signal, but we assumed they were. All spectral data was gathered visually from a Tek 7L13, which is not fast, so although I spent hours staring at it, I am sure a lot of data was missed.
This general idea could be used in amplifier testing, that is, to check slew-induced distortions and actual headroom in the presence of broad-band non-correlated signals. Maybe this is already being done, if so pardon my ignorance.
Howie
Howard Hoyt
CE - WXYC-FM 89.3
UNC Chapel Hill, NC
www.wxyc.org
1st on the internet
I may have missed additional comments on this topic, but a critical aspect of multi-tone testing is whether the tones are phase correlated or not. Once upon a mass tape replication system ago I used a multi-tone signal to check frequency response, and when the tones were digitally synthesized and locked in phase to each other the actual peak levels were far lower (20dB or more in some cases IIRC) than when the test signal was generated by summing 12 multiple free-running analog oscillators. In order to more accurately model compression we used the analog-generated version. Somewhere I have a RDAT with the two compared, and it is remarkable! (thus accounting for my remarks, I guess...
).The remarkable thing we deduced from the tests was at some high record level there were transient holes in the frequency response with distortion peaks depending on the exact delta-v delta-t at each instant; we assumed it was due to slew limitations in the record system. That is to say, in the presence of aligned wavefronts, headroom would be used up on a transient basis, causing odd distortion component generation. We could not catch all of those transient distortion components to see if they were harmonically related to the test signal, but we assumed they were. All spectral data was gathered visually from a Tek 7L13, which is not fast, so although I spent hours staring at it, I am sure a lot of data was missed.
This general idea could be used in amplifier testing, that is, to check slew-induced distortions and actual headroom in the presence of broad-band non-correlated signals. Maybe this is already being done, if so pardon my ignorance.
Howie
Howard Hoyt
CE - WXYC-FM 89.3
UNC Chapel Hill, NC
www.wxyc.org
1st on the internet
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Joachim,
I should have said "align and overlay, where align refers to the time and amplitude adjustments...
Ciao T
I should have said "align and overlay, where align refers to the time and amplitude adjustments...
Ciao T
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