[00940]

http://www.cordellaudio.com/papers/another_view_of_tim.pdf
http://www.cordellaudio.com/papers/another_view_of_tim_II.pdf

 

[castleofargh]

I won't even pretend that I got it, all those links are beyond me.

 
 
 
ok so here is how my non engineer head sees it(feel free to tell me when I'm wrong and make jokes about how stupid I am. I'm going all out on a limb). I hit a cymbal or whatever, and the first sound is the impact instead of the cymbal vibrating from it. the problem would be that first sound and not at all the cymbal vibrating right? so what I should care about is the impact itself where in a small time, the amplitude recorded may have risen pretty fast and pretty high. much faster than a 20khz sine else we wouldn't even care, it would just be usual signal. on an audible level if it's rising much faster than a 20khz signal, I figure I can't hear it right?
 
but on an electrical level, I guess that if the amp isn't fast enough to follow, it ends up trying to make the waves with an offset in amplitude from failing to rise fast enough. and it will then be making distortions untill it gets back on track. is it something like that or did I get the all idea wrong?
because if it's like that, then worst case scenario, it would take less than half of the fastest sine the amp can make to get back on track. and that's only when the transient or whatever first impulse was both super fast and super loud. else it will be corrected a lot faster.
do we really record a lot of those high amplitude super fast stuff? looking even at highres tracks in audacity that doesn't seem to be the case much.so I suspect microphones to fail a bit on those stuff(or maybe I just don't talk at all about the right problem? ^_^)
 
also (again tell me if I'm completely on the wrong planet here) wouldn't just listening to 16/44 music remove those transient sound entirely with the low pass filter anyway?
 
oh and last, I thought that most audio IMD tests were SMPT... something(don't even know what it means ^_^) with 60hz and 7khz. but that wouldn't really tell much about what happens at 20khz right? are IMD from a 20khz wave usually measured?

 

[bigshot]

The fastest transient in music is a quick snare drum hit, which is about 2 to 3 ms. What kind of time frame are we talking about with TIM? If we are talking about a single 20kHz sine wave, we are talking ten times that fast.

 

[lamode]

  The fastest transient in music is a quick snare drum hit, which is about 2 to 3 ms. What kind of time frame are we talking about with TIM? If we are talking about a single 20kHz sine wave, we are talking ten times that fast.

 
I expect that there will be TIM at all times that you are not listening to a steady sinewave, but that doesn't mean it's audible at all times.

 

[bigshot]

I really only care if it's audible. Like jitter. If I can't hear it, it doesn't bother me.

 

[cjl]

  I won't even pretend that I got it, all those links are beyond me.

 
 
 
ok so here is how my non engineer head sees it(feel free to tell me when I'm wrong and make jokes about how stupid I am. I'm going all out on a limb). I hit a cymbal or whatever, and the first sound is the impact instead of the cymbal vibrating from it. the problem would be that first sound and not at all the cymbal vibrating right? so what I should care about is the impact itself where in a small time, the amplitude recorded may have risen pretty fast and pretty high. much faster than a 20khz sine else we wouldn't even care, it would just be usual signal. on an audible level if it's rising much faster than a 20khz signal, I figure I can't hear it right?

The only way that the signal would have a faster slew rate than a 0dBFS 20kHz sine would be if it had a large amount of high amplitude, >20kHz content. This would be very atypical in music. If you want to check an amplifier for slew-related effects, look at measurements involving full-output high frequency signals. If it doesn't have a problem with those, it won't have a slew-related problem with any others.

 

[bigshot]

I guess we can erase TIM from our list and we're back to electronics all sounding the same as long as they are performing to spec.

 

[lamode]

  The only way that the signal would have a faster slew rate than a 0dBFS 20kHz sine would be if it had a large amount of high amplitude, >20kHz content. This would be very atypical in music. If you want to check an amplifier for slew-related effects, look at measurements involving full-output high frequency signals. If it doesn't have a problem with those, it won't have a slew-related problem with any others.

 
As I stated already, there is more to TIM than slew-rate

 

[castleofargh]

 

  I won't even pretend that I got it, all those links are beyond me.

 
 
 
ok so here is how my non engineer head sees it(feel free to tell me when I'm wrong and make jokes about how stupid I am. I'm going all out on a limb). I hit a cymbal or whatever, and the first sound is the impact instead of the cymbal vibrating from it. the problem would be that first sound and not at all the cymbal vibrating right? so what I should care about is the impact itself where in a small time, the amplitude recorded may have risen pretty fast and pretty high. much faster than a 20khz sine else we wouldn't even care, it would just be usual signal. on an audible level if it's rising much faster than a 20khz signal, I figure I can't hear it right?

The only way that the signal would have a faster slew rate than a 0dBFS 20kHz sine would be if it had a large amount of high amplitude, >20kHz content. This would be very atypical in music. If you want to check an amplifier for slew-related effects, look at measurements involving full-output high frequency signals. If it doesn't have a problem with those, it won't have a slew-related problem with any others.

ok thanks, I guess I'll follow bigshot out then.

 

[Speedskater]

  I guess we can erase TIM from our list and we're back to electronics all sounding the same as long as they are performing to spec.

Well we can erase TIM but there still is SID (Slew Induced Distortion) and other distortion and frequency response issues to be concerned about.  Specs don't mean anything.  But tests & measurements by a skilled engineer who knows just what to measure do.

 

[bigshot]

Would any of that not show up in properly measured normal specs... frequency response, THD, dynamic range, noise floor, etc?
 
The original rabbit hole that led to this thread was the statement that two DAPs that measured well beyond the thresholds of human hearing could sound significantly different, because there are things that either can't be measured or aren't normally measured that make a big difference to the sound. Basically, that there is no such thing as audible transparency... everything sounds different even if they measure the same. (Specifically, Ken Rockwell's measurements of the iPhone 5.)

 

[Speedskater]

  Would any of that not show up in properly measured normal specs... frequency response, THD, dynamic range, noise floor, etc?

Way back when, thinking that Total Harmonic Distortion was the only thing that mattered is what started this mess.  Back then it was easy to make a circuit with tonnes of feedback. So the THD dropped to near zero but the circuits were of poor design and other types of distortion sky rocketed. (like IM & SID)

 

[bigshot]

OK. Starting with IM. Google tells me that the JDT (just detectable threshold) for IM is between 2% and 4% with piano music, and 5% with other kinds of music. Are there any consumer amps that get into that range?
 
All of the tests on this subject appear to be from the 1970s. Is this something that isn't a real world problem in amplifier design any more?

 

[lamode]

  OK. Starting with IM. Google tells me that the JDT (just detectable threshold) for IM is between 2% and 4% with piano music, and 5% with other kinds of music. Are there any consumer amps that get into that range?
 
All of the tests on this subject appear to be from the 1970s. Is this something that isn't a real world problem in amplifier design any more?

 
It's still an issue but the research has already been done. Scientists constantly need to find new areas to study.

 

[bigshot]

Can you point to a midrange solid state amp that has an audible problem with this? Any solid state amp that measures above 2% IMD?
 
For instance, I have a $400 Yamaha AV receiver which has an IMD measurement of .0030% and THD of .085% right before the point of clipping which is still WAY below the threshold of audibility. With googling, I'm finding that all of the IMD measurements on AV receivers is down around in the neighborhood of .02% or less. That's 100 times below the threshold of audibility!