Double Blind tests *did* show amplifiers to sound different

[Pluto]

One problem with meters on amplifiers is that they are hardly ever PPMs, and probably never true-peak PPMs, but generally are some sort of VU(ish) average reading meter

Out of interest, here is an image of a classic BBC ‘twin set’ PPM

Of particular interest are the twin needle mechanical instruments – probably very expensive these days (though they were costly enough in their day). Each number represents a 4dB difference (except the bottom division which represents, in effect, an infinite interval down to silence). By convention, the maximum permitted modulation is PPM6.

One really clever aspect of this system (which goes back, in its basic form, to the 1940s) is that the attack time is fast, but not too fast. The attack time is specifically engineered to show only those peaks of sufficient duration to be audible. A meter with an excessively fast attack time results in the average modulation being too low. The electronics incorporate an intentionally slow fallback time (about 3 seconds from 6 to 1) which, combined with the black background, results in a meter that is extremely easy on the eye; it catches everything audible yet seldom bounces around to distraction – a far cry from today's meters designed to catch everything of about 4 samples duration

 

[sergeauckland]

Out of interest, here is an image of a classic BBC ‘twin set’ PPM

View attachment 77032

Of particular interest are the twin needle mechanical instruments – probably very expensive these days (though they were costly enough in their day). Each number represents a 4dB difference (except the bottom division which represents, in effect, an infinite interval down to silence). By convention, the maximum permitted modulation is PPM6.

One really clever aspect of this system (which goes back, in its basic form, to the 1940s) is that the attack time is fast, but not too fast. The attack time is specifically engineered to show only those peaks of sufficient duration to be audible. A meter with an excessively fast attack time results in the average modulation being too low. The electronics incorporate an intentionally slow fallback time (about 3 seconds from 6 to 1) which, combined with the black background, results in a meter that is extremely easy on the eye; it catches everything audible yet seldom bounces around to distraction – a far cry from today's meters designed to catch everything of about 4 samples duration

This is true for line amplifiers and broadcast transmitters, which is why our regulator, Ofcom, doesn't mandate true-peak modulation monitoring, accepting that there may be a (very) small amount of overmodulation. However, this doesn't apply to output metering on power amps where any clipping (the equivalent of going over PPM6) could be very audible if the amplifier goes unstable during overload. That's why even a PPM on a power amp won't tell the whole story. A much better truer story than any VU-type average reading instrument, but still not the whole truth.

As an aside, you may recall the BBC World Service's motto...Nation Shall Peak 6 Unto Nation!

S.

 

[pjug]

Out of interest, here is an image of a classic BBC ‘twin set’ PPM

View attachment 77032

Of particular interest are the twin needle mechanical instruments – probably very expensive these days (though they were costly enough in their day). Each number represents a 4dB difference (except the bottom division which represents, in effect, an infinite interval down to silence). By convention, the maximum permitted modulation is PPM6.

One really clever aspect of this system (which goes back, in its basic form, to the 1940s) is that the attack time is fast, but not too fast. The attack time is specifically engineered to show only those peaks of sufficient duration to be audible. A meter with an excessively fast attack time results in the average modulation being too low. The electronics incorporate an intentionally slow fallback time (about 3 seconds from 6 to 1) which, combined with the black background, results in a meter that is extremely easy on the eye; it catches everything audible yet seldom bounces around to distraction – a far cry from today's meters designed to catch everything of about 4 samples duration

An advantage of a digital display is it make it much easier to do this kind of thing. Anthem's is nice:

 

[Feanor]

First of all.. thank you very much for your input. i really appreciate it.
You must be on the side that the all amps sound the same unless it isn't clipping.
I have been trying to find an answer to my question for a long time and can't find any conclusive comment on this subject.

One side says watt is watt and there is no audible difference unless it's clipping. (which makes perfect science sense)

On the other hand, people say they do observe the sound difference regardless of volume, hear things they hadn't before, voice has higher clarity, bass is stronger even at the same volume. I have been looking at the listings on Audiogon.com and see some amps going for >$10k used
so there must be some kind of justification for it.

I am fairly new to this hobby, but has seen wonderful reviews Amir has done here, and really would like to know what science says about my question.

I have been into hi-for almost 50 years and my experience is that amps can sound different -- which is not to say that I can always and infallibly tell one from another. However I very often can heard differences and these difference cannot simply be dismissed as clipping of other blatant exceeding of the limitations of the amp. This is the personal experience of most audiophiles, FWIW.

Can I prove that I have heard differences? NO, I can't, nor do I care about proving it to others. What I do know is that other people's subject evaluations agree with mine, but, of course, that isn't prove of anything either.

Some forum participants sneer at the suggestion the people can hear differences between amps, (i.e. amps operating within their defined parameters). They cite blind ABX testing as "proving" that people cannot hear differences where volumes are controlled to within, say. 0.5 dB. Such test regimes might be scientifically rigorous and repeatable, however they are so restrictive that they limit they limit there own results to practical irrelevance.

 

[SIY]

If you have to peek to hear a difference, you can’t actually hear a difference. Trust your ears.

 

[Sgt. Ear Ache]

Such test regimes might be scientifically rigorous and repeatable, however they are so restrictive that they limit they limit there own results to practical irrelevance.

lol...no they don't

 

[Putter]

I have been into hi-for almost 50 years and my experience is that amps can sound different -- which is not to say that I can always and infallibly tell one from another. However I very often can heard differences and these difference cannot simply be dismissed as clipping of other blatant exceeding of the limitations of the amp. This is the personal experience of most audiophiles, FWIW.

Can I prove that I have heard differences? NO, I can't, nor do I care about proving it to others. What I do know is that other people's subject evaluations agree with mine, but, of course, that isn't prove of anything either.

Some forum participants sneer at the suggestion the people can hear differences between amps, (i.e. amps operating within their defined parameters). They cite blind ABX testing as "proving" that people cannot hear differences where volumes are controlled to within, say. 0.5 dB. Such test regimes might be scientifically rigorous and repeatable, however they are so restrictive that they limit they limit there own results to practical irrelevance.

And if you can't hear a difference then you're not an audiophile, i.e. you don't have good ears or the right speakers or the a good enough source and blah blah blah.......

I find it fascinating that when there are so many more significant 'distortions' in the audio chain (room effects, speaker distortions many times that of an amp, speakers that have bad frequency response and/or poor dispersion) and solutions like room eq and addition of subwoofers to ameliorate these problems that we're still hung up on what are at worst the infinitesimal distortions of amps run within their limits when there more important fish to fry.

 

[BDWoody]

Can I prove that I have heard differences? NO, I can't. ... What I do know is that other people's subject evaluations agree with mine, but, of course, that isn't prove of anything either.

Exactly...

Waiting for someone to actually do more than claim it.

 

[Sgt. Ear Ache]

And if you can't hear a difference then you're not an audiophile, i.e. you don't have good ears or the right speakers or the a good enough source and blah blah blah.......

I find it fascinating that when there are so many more significant 'distortions' in the audio chain (room effects, speaker distortions many times that of an amp, speakers that have bad frequency response and/or poor dispersion) and solutions like room eq and addition of subwoofers to ameliorate these problems that we're still hung up on what are at worst the infinitesimal distortions of amps run within their limits when there more important fish to fry.

exactly. Most normal rooms have ambient noise levels upwards of 30dbs and people think they can hear distortion and distinctions that are happening at sub 1db levels. Just sitting with your head in a spot a few inches off from where you were yesterday is going to have way more impact on the sound you're hearing from your system than what occurs from different amps (assuming they measure the same within audible parameters of course. If an amp is measurably coloring the signal in some way - for some reason - then obviously you might hear a difference.)

 

[Feanor]

And if you can't hear a difference then you're not an audiophile, i.e. you don't have good ears or the right speakers or the a good enough source and blah blah blah.......

I find it fascinating that when there are so many more significant 'distortions' in the audio chain (room effects, speaker distortions many times that of an amp, speakers that have bad frequency response and/or poor dispersion) and solutions like room eq and addition of subwoofers to ameliorate these problems that we're still hung up on what are at worst the infinitesimal distortions of amps run within their limits when there more important fish to fry.

Sneer all you like, Putter, alters my opinion not one iota.

I didn't say anything to the effect that only audiophiles could hear differences -- don't put words in my mouth, thanks. In fact I have average hearing a best, maybe less than average given my age, etc. What I do -- which you might not -- is LISTEN without the prejudice that there are no differences to be heard. (Who's the bigot now?)

As for room distortions, etc., sure, but if all else is equal except the amps, then it's the amp difference you're hearing.

 

[Sgt. Ear Ache]

As for room distortions, etc., sure, but if all else is equal except the amps, then it's the amp difference you're hearing.

you mean imagine you're hearing.

 

[Feanor]

If you have to peek to hear a difference, you can’t actually hear a difference. Trust your ears.

Not the first time I've been the butt of your sneering, SIY.

Decades have passed since audiophiles were tempted to believe that the differences they were hearing are only their imaginations.

In fairness, though, I'm not a big believer myself in difference between, say, power cords.

 

[Feanor]

you mean imagine you're hearing.

OK ... and good enough to convince me.

 

[SIY]

IOW, you don’t trust your ears. That’s your choice. Some people prefer make believe.

 

[Sgt. Ear Ache]

Decades have passed since audiophiles were tempted to believe that the differences they were hearing are only their imaginations.

Actually, too many decades have passed during which many audiophiles have allowed themselves to be fooled by cognitive bias regarding what they think they are (or are even capable) of hearing.

 

[Pluto]

this doesn't apply to output metering on power amps where any clipping (the equivalent of going over PPM6) could be very audible if the amplifier goes unstable during overload

To what extent is “unstable during overload” due to the operation of some misbegotten protection system as opposed to an amplifier merely being allowed to generate square-ish waves which is what happens to most circuits when mildly over-driven?

 

[amirm]

So, using 4 ohm speakers is NOT normal for amp without power rating into 4 ohm at all. Not even considering that 4 ohm rated speaker is absolutely not a resistor.

With respect to amplifiers in AVRs, they don't want to specify them for 4 ohm for regulatory reasons (requires passing a heat rise test that is hard for them). But they absolutely work with 4 ohm loads. They have to as vast number of speakers have impedances that dip below 4 ohm. Hence the reason I test them with 4 ohm loads.

 

[Feanor]

In fairness, though, I'm not a big believer myself in difference between, say, power cords.

IOW, you don’t trust your ears. That’s your choice. Some people prefer make believe.

Well a couple of things ...

• I don't hear differences between power cords, and
• No, I don't always "trust my ear" ... though sometimes I do.

 

[Feanor]

Actually, too many decades have passed during which many audiophiles have allowed themselves to be fooled by cognitive bias regarding what they think they are (or are even capable) of hearing.

Believe it or not at this stage, I agree with you.

To be sure, some audiophiles believe they hear difference between AC cables, Cat5e cables where I have never heard a difference. When it comes to interconnects or op amps, I've thought I heard small differences but the difference were so small that I felt I could trust what I thought I heard.

... But I have heard difference between amplifiers and been sure of them. See a recent review I wrote ... https://www.audioasylum.com/forums/amp/messages/23/235714.html ... a subjective review of course.

 

[sergeauckland]

To what extent is “unstable during overload” due to the operation of some misbegotten protection system as opposed to an amplifier merely being allowed to generate square-ish waves which is what happens to most circuits when mildly over-driven?

A well designed power amp will clip cleanly and recover quickly and still be properly protected. e.g. all of Quad's SS amps were that way. Clean clipping and no sign of instability. Others, as Amir posted early on in the thread, show unstable behaviour. I've had some amps on my bench that looked similar to what Amir posted, so those an be expected to sound rough on overload. Whether it's due to a poor protection system or the collapse of feedback or marginal stability even when operating normally, I don't know as I didn't investigate. Probably the worse I've seen was a valve amplifier that went cleanish up to full power, but then flipped to sudden horrible distortion with a further small increase in level.
S