Incorporating Burst Power and Slew Rate Tests for Amplifier Reviews

[SIY]

No

OK, so you have nothing. Literally.

 

[AdamFrandsen]

Except that is not what happens. The amp is not clipping - why would it unless the peak input waveform x gain was greater than the maximum output voltage.

What must be avoided is the derived waveform from all the individual tones (out of the analyser) clipping (>0dBFS) due to all the individual tones periodically lining up so that they are all at the peak at the same time. So if you have 124 tones, then you have to reduce them all in amplitued by FS/124 (about -42dB) so when they all stack up it comes to less than 0dB FS.

Even when attenuated to -42db, intermodulation might add to the energy and cause localized clipping, no? Phase interactions? I would furthermore suggest adjusting the amplitude according to the occurrence of the frequencies in real music such as:

Frequencies in 20-200 Hz are scaled to 30-50% of the peak amplitude.
Frequencies in 200-2,000 Hz are set at full amplitude (100%).
Frequencies in 2,000-20,000 Hz are scaled to 40-60% of the peak amplitude.

 

[Multicore]

Even when attenuated to -42db, intermodulation might add to the energy and cause localized clipping, no? Phase interactions?

You can understand "The amp is not clipping..." is in this context as synonymous with "the amp is linear". Hence: no. And no.

I would furthermore suggest adjusting the amplitude according to the occurrence of the frequencies in real music such as:

Frequencies in 20-200 Hz are scaled to 30-50% of the peak amplitude.
Frequencies in 200-2,000 Hz are set at full amplitude (100%).
Frequencies in 2,000-20,000 Hz are scaled to 40-60% of the peak amplitude.

I have several questions.

1. How did you derive this spec?
2. Is this a design for specifying a multi-tone test signal?
3. What do we take as peak amplitude?
4. What do we take as full amplitude?

 

[Titurel]

Standard tuning: I listed all the frequencies already. The point is not to be so precise that you have to include small variations in tuning, but that, in most modern music, there are only 124 notes within the audible spectrum - not thousands - so you could use them to test in a way that is more closely related to real music signals, even if it is not always the precise tuning. Also, lowering the signals to, say, -20 dBFS is doable, no? Finding out when the amp clips due to complex signals is valuable information. Additionally, one could use logarithmic scaling as well as zoomed-in frequency ranges to make it fit visually.

You've kind of missed the point. So called standard tuning is not standard at all. It's actually a bit of a fallacy. What I believe you are referring to is the tempered scale, a product of the 19th century* which facilitates keyboard instruments playing (equally out of tune) in all the keys of the Western diatonic scale. It is really not relevant to generalized discussions of music and audio other than indicating the nominal compass of some standard instruments. Even instruments as apparently similar as the piano and pipe organ are tuned very differently. In fact, pianos of different sizes are tuned differently, even if they share the same nominal (or standard) set of keys.

In any case, a truly useful test signal should reveal worst case performance (when reproducing music), even if the signal is not a close analog of music. The signal suite you propose is more complicated, but I can't see where it is necessarily any more illuminating.

* The problem which it (imperfectly) addresses was recognized centuries earlier.

 

[kyuu]

I think it's clear at this point that the OP is more interested in testing that assuages his aesthetic sensibilities rather than furthering any technical objective.

 

[antcollinet]

Even when attenuated to -42db, intermodulation might add to the energy and cause localized clipping, no? Phase interactions? I would furthermore suggest adjusting the amplitude according to the occurrence of the frequencies in real music such as:

Frequencies in 20-200 Hz are scaled to 30-50% of the peak amplitude.
Frequencies in 200-2,000 Hz are set at full amplitude (100%).
Frequencies in 2,000-20,000 Hz are scaled to 40-60% of the peak amplitude.

You seem to be under the weird misapprehension that an amplifer knows what music looks like, and that therfore if a test signal doesn't look exactly like music the amp will behave differently with it.

That is not the case. The amp looks at a signal and amplifies it - it really doesn't care what that signal is. There are obvious signal dependent behaviours such as IMD, but these are all pretty well understood and consistent - and the existing test signals have already been optimised to trigger those behaviours.

Beyond that it doesn't matter at all if the spectral power density matches typical music - in fact having a flat multitone actually stresses the amp much more - for example, by maximising the "slew rate" you were so worried about upthread, by having high level high frequency content - much much higher level than music contains.

 

[Titurel]

I think it's clear at this point that the OP is more interested in testing that assuages his aesthetic sensibilities rather than furthering any technical objective.

I'd be a bit more careful attributing motives. I don't agree with the OP's 124 note test signal proposal, but I'd agree that the current state of audio reproduction, while very good, if not yet as close to perfect as some on this forum believe.

 

[kyuu]

I'd be a bit more careful attributing motives. I don't agree with the OP's 124 note test signal proposal, but I'd agree that the current state of audio reproduction, while very good, if not yet as close to perfect as some on this forum believe.

What else is one supposed to think when he is rejecting all technical arguments and arguing that amplifier tests need to be based on Western music notation? Nevermind making comparisons to architecture he finds pleasing.

 

[Timcognito]

I'd agree that the current state of audio reproduction, while very good, if not yet as close to perfect as some on this forum believe.

I may be jumping off a cliff here, as my knowledge of electronics is rudimentary but the problems in good electronics design have been solved well beyond the audibility range. The issues lie in the transduction from mechanical energy (sound) to electric and back to mechanical sound.

 

[LTig]

I'd be a bit more careful attributing motives. I don't agree with the OP's 124 note test signal proposal, but I'd agree that the current state of audio reproduction, while very good, if not yet as close to perfect as some on this forum believe.

But this is a problem of the transducers (microphones and speakers), not electronics.

 

[Multicore]

Beyond that it doesn't matter at all if the spectral power density matches typical music

And as we have seen recently in a few different threads, there's no such thing as typical music.

 

[Multicore]

I'd be a bit more careful attributing motives. I don't agree with the OP's 124 note test signal proposal, but I'd agree that the current state of audio reproduction, while very good, if not yet as close to perfect as some on this forum believe.

This is interesting. What are the drawbacks of current state of audio reproduction? What do some on this forum incorrectly believe?

 

[Titurel]

And as we have seen recently in a few different threads, there's no such thing as typical music.

My sense of what is typical is clearly broader than the OP's, possibly broader than yours, and pretty much independent of my taste. I think a lot of today's popular stuff is excrement, but I will concede it's music and not extraordinary, i.e., it's typical. Including a Saturn V booster in your ensemble, is probably atypical, as I don't think you can get a musician union card as a Saturn V player.

So, there is such a thing as typical music. The risk (of error) is capriciously defining its borders.

 

[AdamFrandsen]

My sense of what is typical is clearly broader than the OP's, possibly broader than yours, and pretty much independent of my taste. I think a lot of today's popular is excrement, but I will concede it's music and not extraordinary, i.e., it's typical. Including a Saturn V booster in your ensemble, is probably atypical, as I don't think you can get a musician union card as a Saturn V player.

So, there is such a thing as typical music. The risk (of error) is capriciously defining its borders.

What a load of nonsense... Sorry, but seriously

 

[Cbdb2]

What a load of nonsense... Sorry, but seriously

Out of common courtesy Im pretty sure a lot of people here, my self included, have refrained from saying most of your posts are a load of nonsense.

 

[kemmler3D]

Finding out when the amp clips due to complex signals is valuable information.

That's not really how amps work. Amps clip because the signals get too large, not because of what they are.

Also, there is nothing special about musical notes when it comes to amps, just like pictures of flowers don't have any special relationship to how TVs work.

Amps have an upper and lower frequency cut-off, a maximum power output, and in between all signals should behave the same. The tests Amir performs generally give us enough information to judge how well the amp meets that goal. We can generalize from the 32-tone test to a 128-tone test or whatever complex signals (music) you actually care about.

 

[Titurel]

What a load of nonsense... Sorry, but seriously

Absolutely serious. What constitutes music is a vastly complex subject. After >50 years in the music business, I'm still learning (and laughing).

 

[Sokel]

What a load of nonsense... Sorry, but seriously

If your reasons are aesthetic and interested in interactions ditch the well tempered stuff and start fresh from Lydian and Phrygian scales where can result in interesting finds.
Leave the electronics for later.

 

[kemmler3D]

Absolutely serious. What constitutes music is a vastly complex subject. After >50 years in the music business, I'm still learning (and laughing).

After doing a few art history classes, I came to the conclusion that trying to draw a line between "art" and "not art" serves little purpose and usually ends up making the line-drawer look foolish later on. So I figure if you have at least one "musician" and at least one listener willing to call something music, then it's music, and I'm willing to be convinced on the necessity of a listener.

My bar is much higher for "good" or even "worthwhile" music.

 

[AdamFrandsen]

Out of common courtesy Im pretty sure a lot of people here, my self included, have refrained from saying most of your posts are a load of nonsense.

You again seem to think this is a competition or battle you have to win.