I concur this is all great food for thought. I think in general the time element is very poorly understood, I can can pass my finger at high speed through a blowtorch without damage, yes maybe a coarse analogy but it is important.
Another point is that over the years I have learned that at the very smallest and largest extremes our everyday physics rules deviate, not to say that Mitch Cotter is right in saying there are quantum mechanical aspects to playing vinyl.
Hi Scott, Re #1282 Your question. "Reference?"
I am out of my depth with the mathematics of this thread but I do recall seeing an article in "Electronics World" (ex UK 'Wireless World') during the past decade written by an RF engineer (radar background, I think) who discussed multi tone tests for RF equipment and he pointed out the rapidly worsening IM products appearing as "a carpet" as the number of tones used increased.
I also think that when he drew out the implications for AUDIO frequencies he scored a bit of "flak". That's as much as I remember. But at the time it put the fear of God into some people about the importance of IM.
Some of our UK members may be able to give us more precise data re; dates, editions etc.
Jonathan
I am out of my depth with the mathematics of this thread but I do recall seeing an article in "Electronics World" (ex UK 'Wireless World') during the past decade written by an RF engineer (radar background, I think) who discussed multi tone tests for RF equipment and he pointed out the rapidly worsening IM products appearing as "a carpet" as the number of tones used increased.
I also think that when he drew out the implications for AUDIO frequencies he scored a bit of "flak". That's as much as I remember. But at the time it put the fear of God into some people about the importance of IM.
Some of our UK members may be able to give us more precise data re; dates, editions etc.
Jonathan
It is true that the 'grass' increases - it's just that a multitude of distortion products appear that look like grass. But you are not looking at that grass in total. The idea is to space the multitones such that the distortion product fall, in discrete FFT bins and can thus be analysed easier. For instance, if you would be interested in IMD products from bass tones you would look in the bins that hold the IMD products from the lowest signal components. At the same time you can look at the 2nd and 3rd HD products from say the 6.236kHz signal component. All from the same one-time acquisition. Etc.
jan
SY,
May I invite you to another OT comment. In my experience working with PVC, it appears to have a non-linear viscosity c.q. elasticity modulus under acceleration. Couldn't find anything on it on the interwebs, and my observation may be mistaken. But if so, it might partly explain why LP's work as well as they do.
vac
Non-Newtonian liquids
Many long-chain polymers display non-Newtonian shear and flow characteristics, especially near state transitions. This characteristic is taken advantage of with viscosity improvers in lubricants.
Howie
Howard Hoyt - WA4PSC
CE - WXYC-FM 89.3
UNC Chapel Hill, NC
www.wxyc.org
1st on the internet
Many long-chain polymers display non-Newtonian shear and flow characteristics, especially near state transitions. This characteristic is taken advantage of with viscosity improvers in lubricants.
Howie
Howard Hoyt - WA4PSC
CE - WXYC-FM 89.3
UNC Chapel Hill, NC
www.wxyc.org
1st on the internet
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MultiTones tests for opamp -
MultiTones -- It may be enough to have a look at total distortion rise/growth of the 'grass', at first, just for seperating our opamp designs. ?? To see what happens when many signals are passing thru opamp simultaneously.... as with actual useage. Then, later, break-down into details of differences. We can see the rise in total between designs. It is IMO most important to test a product under conditions of actual use or simulated actual use. -RNM
MultiTones -- It may be enough to have a look at total distortion rise/growth of the 'grass', at first, just for seperating our opamp designs. ?? To see what happens when many signals are passing thru opamp simultaneously.... as with actual useage. Then, later, break-down into details of differences. We can see the rise in total between designs. It is IMO most important to test a product under conditions of actual use or simulated actual use. -RNM
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I have used MTPR (multi-tone power ratio) to characterize xDSL drivers for over 15years. I was just saying before that "20dB rise for 2X the tones" is not my experience. There are many ways to mess up interpretation of these tests like not maintaining equal width bins, equal total power in the sum of the tones, and matching crest factor.
Another very important point is that smooth nonlinearities operate over the full amplitude range while crossover issues only at the zero crossings (crest factor does not matter as much).
Sure - and multitones are no cure for all ills. I believe the reason for them was the desperate search for a measurement that correlate with listening. The idea that circuits somehow react different to multitones than to single tones. I don't believe that to be true; a nonlinearity acts the same on whatever signal you throw at it. "We don't litsen to sineswaves, we listen to music" sounds like a nice phrase but is a strawman at best - all music is basically a bunch of sinewaves, after all.
One obvious advantage of multitones is that you can extract a lot of parameters from a single short test signal, and that is important in broadcasting for example where the off-air time must be very short.
But I doubt it will tell you more about how to change your design for better sound than, say, a swept THD and IMD test and a check for sufficient slewrate (although the latter is really enclosed in the former).
jan
Testing the opamp
The 20db increase (above an amps' noise floor) was from actual tests using AP multitone on certain amps. The point being, if the total increase with many tones exceeds the Audible threshold or not.
That is not what you can determine with 1-2 or 3 tones. yes, you can figure if the amp is very good or not. But not My point of the tests. Correlation to audible effects is My first point. The multiTone test can better determine whether under close to normal useage if the threshold is breached. We can get into masking if it happens and that is a can of worms for another thread.
Also, yes, there are many tests to determine various aspects of the circuit's performance. Which ones are we going to require. All we get now is THD or individual harmonic levels with a sine wave or two and say Wow! isnt that wonderful and that it is so low no one can hear it.
[ I would also be interested if the audible threshold is exceeded by the sum total of all the equipment in the music playback system... source to speaker terminal on the power amp]
Thx,
Richard
The 20db increase (above an amps' noise floor) was from actual tests using AP multitone on certain amps. The point being, if the total increase with many tones exceeds the Audible threshold or not.
That is not what you can determine with 1-2 or 3 tones. yes, you can figure if the amp is very good or not. But not My point of the tests. Correlation to audible effects is My first point. The multiTone test can better determine whether under close to normal useage if the threshold is breached. We can get into masking if it happens and that is a can of worms for another thread.
Also, yes, there are many tests to determine various aspects of the circuit's performance. Which ones are we going to require. All we get now is THD or individual harmonic levels with a sine wave or two and say Wow! isnt that wonderful and that it is so low no one can hear it.
[ I would also be interested if the audible threshold is exceeded by the sum total of all the equipment in the music playback system... source to speaker terminal on the power amp]
Thx,
Richard
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Need some pictures again. My experience is that 1/2 the tones at the SAME TOTAL power has exactly the same average "grass" unless there is something pathological in the signal path. I will try to show a simple example if I have time.
I think the best candidate so far is the design Scott offered, perhaps amended with some cascoding of the BF862 and with an optimized output buffer. However, we will never have "one size fits all" when the various and shifting wish lists are considered. It's just not in the nature of the beast.
Nor do I think that was to be the point of the exercises. Had it been, the first thing to have agreed upon would be a comprehensive list of specifications.
But I've enjoyed the ride so far.
I'm a layman audiophile that builds my own gear and I don't pretend to be on the same level with you guys. I've built several discreet opamps, Two designed at Georgia Tech by Marshall Leach (RIP). My list of wants is simple; + and- 24v rails (ie plenty of headroom), servo dc offset detection, as few compensation capacitors as possible, preferably jFET front end, and a well regulated power supply. There probably should be one with a gain of around 100 for RIAA, CCIR/NAB tape and flat Microphone EQ. Another design for post volume control with a gain of about 10, It would be great if the output were balanced without a transformer and capable of driving 50 feet of cable to the power amp. John Curl's little preamp with the mje243 and mje253 output and the j113 and j175 jfet looks nice to me. Just my two cents. Thanks for listening. Ray
