Back to the sound of cables..
I can't wait until some researcher actually tests human hearing in the way we actually hear. Not some ITD, or IID, or ITD vs ITD setup. Entirely artificial.
Artificial, like a pan pot. Not what we actually hear and sense.
I had proposed the 100 usec/.1dB shifted test signal set for one very specific reason....standard recorded media does not deal with the two channels accurately enough to simulate what we have evolved to hear. Even that research that somebody earlier in this thread cited (I asume it was not his own research, even though no attribution was given) gave that 220 usec number (which was inaccurate) for ear to ear delay.
Sy, I certainly concur.. If an IC makes a difference, it is the fault of either the environment, or the equipment.
If a speaker cable can make a difference, then what do the speaker designers use??????
I have proposed in the past, several new test methods to detect these shortcomings in existing methods.
Anyone game?
Till monday.
Cheers, John
I can't wait until some researcher actually tests human hearing in the way we actually hear. Not some ITD, or IID, or ITD vs ITD setup. Entirely artificial.
Artificial, like a pan pot. Not what we actually hear and sense.
I had proposed the 100 usec/.1dB shifted test signal set for one very specific reason....standard recorded media does not deal with the two channels accurately enough to simulate what we have evolved to hear. Even that research that somebody earlier in this thread cited (I asume it was not his own research, even though no attribution was given) gave that 220 usec number (which was inaccurate) for ear to ear delay.
Sy, I certainly concur.. If an IC makes a difference, it is the fault of either the environment, or the equipment.
If a speaker cable can make a difference, then what do the speaker designers use??????
I have proposed in the past, several new test methods to detect these shortcomings in existing methods.
Anyone game?
Till monday.
Cheers, John
serengetiplains said:
No because you have still run away from it, real or unreal.
Then you get into processing and pattern recognition. That's where the mind really starts to play tricks on you...
pinkmouse said:
You got that right.
Many people have this notion that the ear is rather like a microphone which captures everything and passes it on to the brain. Nothing could be farther from the truth. The ear throws out a tremendous amount of information which never even makes it to the brain and our perception of sound is in good part an interpolation on the part of the brain of what relatively little information it actually receives.
se
Test signals that are more like music
Music has a very large peak to average and average to smallest signal ratio. One piece of test equipment that might help designers determine why some amplifiers (or cables - who said that? 😱 ) sound better than others, would be a modification of the gain linearity test I have seen used for years on video signals but never for audio.
The test signal consists of a steady state sine wave, say 1Khz supperimposed on a staircase waveform in such a way that many cycles of the sine wave occupy each step. The stair case might have ten steps. Now this signal is applied to an amplifier in such a way that the top and bottom steps are short of both positive and negative clipping. The resulting signal is taken from the output terminals and filtered so as to remove the stair steps but not the sine wave. The measurement consists of verifying that the sine wave is amplified by exactly the same gain at each point on the stairstep. It is very easy to see errors on an oscilloscope because the sine wave will show signs of AM modulation at the stair step frequency.
Using modern DSP signal construction techniques to make it closer to a musical signal I would sum in a tone burst of a different frequency at the center of each step. This tone burst of either lower or higher frequency than the !KHZ wave would be adjusted to equal the peak to peak swing of the total waveform.
There is a drawing below. Due to limitations of tools and drawing time, this is not to scale. The bursts should be longer. The size of the small sine wave should be adjustable by the tester to cover a range of say -10dB down to -60dB. Neither stair step nor large burst would modulate the small sine wave in an ideal amplifier.
Hi jneutron, glad to see you're here and paying attention.jneutron said:
Music has a very large peak to average and average to smallest signal ratio. One piece of test equipment that might help designers determine why some amplifiers (or cables - who said that? 😱 ) sound better than others, would be a modification of the gain linearity test I have seen used for years on video signals but never for audio.
The test signal consists of a steady state sine wave, say 1Khz supperimposed on a staircase waveform in such a way that many cycles of the sine wave occupy each step. The stair case might have ten steps. Now this signal is applied to an amplifier in such a way that the top and bottom steps are short of both positive and negative clipping. The resulting signal is taken from the output terminals and filtered so as to remove the stair steps but not the sine wave. The measurement consists of verifying that the sine wave is amplified by exactly the same gain at each point on the stairstep. It is very easy to see errors on an oscilloscope because the sine wave will show signs of AM modulation at the stair step frequency.
Using modern DSP signal construction techniques to make it closer to a musical signal I would sum in a tone burst of a different frequency at the center of each step. This tone burst of either lower or higher frequency than the !KHZ wave would be adjusted to equal the peak to peak swing of the total waveform.
There is a drawing below. Due to limitations of tools and drawing time, this is not to scale. The bursts should be longer. The size of the small sine wave should be adjustable by the tester to cover a range of say -10dB down to -60dB. Neither stair step nor large burst would modulate the small sine wave in an ideal amplifier.
Attachments
I was, like, listening to a grooving cd (Collective Soul) singing along with the song when my wife suggested I sing along to the song that actually was playing (Johnny Cash). Can you believe my brain would play such a trick on me?? Silly brain!
It is also the choice in the DC world. We have to silver plate anything we do which is over 5 kiloamps.rdf said:
John
Yep,
A great material for relays too... the by-product of arcing is conductive, thereby helping to ensure, not only contact, but another cleansing arc on the next contact closure.
A great material for relays too... the by-product of arcing is conductive, thereby helping to ensure, not only contact, but another cleansing arc on the next contact closure.
This is quite a clever linearity test IMO. Why not use a variable low-frequency sinusoidal instead of a step function if an audio amp is to be measured ? The auxiliary sinusoidal should be chosen so that its harmonics aren't related to the reference sine wave. The reference sine wave should also be chosen that it doesn't lay on any harmonics of the mains voltage.
It should be possible to build such a device in quite a simple/cheap fashion IMO.
Regards
Charles
phase_accurate said:
I think this was first used in the landmark series on slewing induced distortion by Walt Jung and Mark (or was it Craig?) Todd. They showed exactly these types of waveforms. Audio Amateur 1978, I think. AES before that.
Jan Didden
Re: Test signals that are more like music
Hey, wouldn't miss it..
I am concerned that it may be very difficult to distinguish between cable effects and amp effects.
I also worry about the circuit's response (both dut and measuring instrument) to the abrupt change in slew rates. I've been bitten by input pair issues before.
The filter ability to remove the modulating wave while leaving the wanted signal would also be a concern for me.
If I were to assemble a circuit to test a cable, I'd do this:
Create a standard cable, coaxial, with a characteristic impedance of 10K. Actually, create two..
Create a two input summing node which shows a 10K impedance at each input. The standard cable is attached to one of the nodes.
Create a differential output drive circuit, one which has zero output impedance, two outputs, and equal but opposite signals at each output. Low Zout is imperative to keep differential loading from playing a part..
Both the drive and the summing node need bandwidths that exceed requirement by two orders of magnitude. I personally would go out to a Ghz, just to assure myself that within the audio band, the test setup is accurate.
Connect both standard cables to the system, and assure that a null exists at the output of the summer. Do so for signals well above audio, 100 Mhz would be good enough.
This setup gets away from the possibility of circuit based anomolies, and allows one to view directly any difference between the responses of the cable under test.
Once familiar with this setup, one can insert various source resistors, and watch the cable's reaction to various inputs. For example, if the DC of the insulator changed with voltage, this could be spotted..all kindsa fun tests..
Cheers, John
hermanv said:
Hey, wouldn't miss it..
I am concerned that it may be very difficult to distinguish between cable effects and amp effects.
I also worry about the circuit's response (both dut and measuring instrument) to the abrupt change in slew rates. I've been bitten by input pair issues before.
The filter ability to remove the modulating wave while leaving the wanted signal would also be a concern for me.
If I were to assemble a circuit to test a cable, I'd do this:
Create a standard cable, coaxial, with a characteristic impedance of 10K. Actually, create two..
Create a two input summing node which shows a 10K impedance at each input. The standard cable is attached to one of the nodes.
Create a differential output drive circuit, one which has zero output impedance, two outputs, and equal but opposite signals at each output. Low Zout is imperative to keep differential loading from playing a part..
Both the drive and the summing node need bandwidths that exceed requirement by two orders of magnitude. I personally would go out to a Ghz, just to assure myself that within the audio band, the test setup is accurate.
Connect both standard cables to the system, and assure that a null exists at the output of the summer. Do so for signals well above audio, 100 Mhz would be good enough.
This setup gets away from the possibility of circuit based anomolies, and allows one to view directly any difference between the responses of the cable under test.
Once familiar with this setup, one can insert various source resistors, and watch the cable's reaction to various inputs. For example, if the DC of the insulator changed with voltage, this could be spotted..all kindsa fun tests..
Cheers, John
fcserei said:
What is the source of this information?
220 uSec at 13,620 inches per second, is a path length differential of 3 inches.
At 45 degrees, with the source at infinity, path length difference is 3 times sqr(2), or 4.24 inches. This is 308 uSec. This of course, does not take into consideration, the fact that the longer path also has to wrap around the head to get to the ear, this in itself introduces additional delays and frequency filtering....4.24 inches is a simple line of sight calculation.
As the distance from the source decreases, with the source still at 45 to the head center, the path differential increases, being 311 uSec at 40 inches by 40 inches (56.5 inches from head center).
I don't know about you, but I have indeed sat in between two speakers with a mono source playing, and certainly visualized a single virtual source in the middle of the field, independent of the variations in angle typical of a head not being in a vice...so your statement ""Of course pinna direction finding patterns will still tell your brain that you are listening to 2 seperate sources several feet apart, not a single source at 20 deg."" is entirely inconsistent with what I have personally experienced.😕 😕 😕 I do not understand why nobody else here has questioned that assertion..😕
Cheers, John
Yes, SID is always a potential problem with square waves. Many amplifiers have a simple RC input lowpass so that input signals cannot drive the amp into slew rate limiting. IMHO, all should.
As for two speakers playing a mono source, if the signals are in phase, you should get a very stable, centrally located "image". If it moves with frequency, the speakers have dissimilar frequency responses. Hearing two speakers, separated, means that one channel's phase is reversed. Good quick test in fact for testing phasing when setting up.
As for two speakers playing a mono source, if the signals are in phase, you should get a very stable, centrally located "image". If it moves with frequency, the speakers have dissimilar frequency responses. Hearing two speakers, separated, means that one channel's phase is reversed. Good quick test in fact for testing phasing when setting up.
For the Audiophile who has everything....
Introducing the P3z DC Power Interconnect...
http://av123forum.com/showthread.php?threadid=11713
😉
- Audioferret
Introducing the P3z DC Power Interconnect...
http://av123forum.com/showthread.php?threadid=11713
😉
- Audioferret
Re: For the Audiophile who has everything....
What is it, and why is is better?
John
audioferret said:
What is it, and why is is better?
John
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