Do amplifiers really sound the same?

[sergeauckland]

Yes. But not just any people.

Imagine two components that are seemingly indentical, except for a subtle difference in their presentation of the stereo image.

When presentated to non-enthusiasts this may well go unnoticed, as it is suspected that people not seriously engaged in audio/music hardly perceive stereo imaging.

Even when confining the test to experienced listeners this still may happen. I myself am mostly deaf to imaging when presented with an alien system and/or an alien room. In some cases it takes me several hourse of listening before I am able to decode what the speakers are hurtling at me.


So ideally difference testing is done on large populations, but the subjects must be of sufficient training, and they must be in a sympathetic environment.

I take blind testing results stemming from large amounts of people dumped in arbitrary rooms with arbitrary systems and arbitrary music with a large pinch of salt.

And so the ultimate ABX test appears to be rather impractical.

I agree about trained observers. A blind test for testing small sonic differences between amplifiers would be pretty pointless just pulling people off the street.

On the other hand, if, for example, the purpose of the test was to see what completely untrained people make of stereo, or what they can or can't appreciate, then using untrained people would be necessary. So it rather depends on the purpose of the test who the best subjects are.

S.

 

[Dik Dolan]

But all amps DO measure differently. It's all down to degree....

Oh, and those 2 pictures..... near top left corners, one has a big "1" and the other has a "2" =)

 

[Robert]

That's nothing like optical performance or audio presentation so now the analogy is getting completely strained. What we have here are two very busy images which are identical apart from a number of manipulated details. It would be like trying to distinguish between the same recording played twice on the same equipment except that in one case a few single notes were edited out or changed. In both cases, the photos above and the hypothetical recording, the differences are objectively present and perceptible.

Plus music is transient in nature and we are processing it for very short periods of time. Not the same thing at all staring at a static object and analysing it.

 

[cooky1257]

And what of the none flat and famous BBC dip?

 

[sergeauckland]

But all amps DO measure differently. It's all down to degree....
Oh, and those 2 pictures..... near top left corners, one has a big "1" and the other has a "2" =)

Yes of course they do, but as I've said repeatedly, if their performance exceeds a certain threshold, which can be argued over perhaps, but nevertheless, if two amplifiers are both transparent, then regardless of how they measure, they will sound the same. 0.05% THD will sound the same as 0.001%. A frequency response -1dB @ 20kHz will sound the same as -1dB at 100kHz, and so on.

S.

 

[Robert]

But all amps DO measure differently. It's all down to degree....

Oh, and those 2 pictures..... near top left corners, one has a big "1" and the other has a "2" =)

One can of Heinz baked beans is always slightly different to another.
Does it matter, is it relevant and would you expend any effort on analysis?
Of course not.

Would you noticed if I swapped Heinz for HP?
Yes you probably would.

 

[Dik Dolan]

Indeed Serge, but then it comes down to definitions of transparency. My definition would be an amp that does nothing to the signal apart from amplify it. No amps can pass this test, therefore no amps are totally transparent, and its just down to chosing the flavouring/filtering that I prefer. A subjective choice.

 

[sergeauckland]

And what of the none flat and famous BBC dip?

What about it? It was developed to allow better descrimination of HF issues, especially stereo positioning when balancing music for transmission. It also helped with the audibility of the 15.6kHz TV line whistle, as that was a concern when TV monitors started to be used for visual feedback, and there was some concern about this 15.6kHz whistle being picked up by microphones.

Note that the BBC made very little use of EQ, so using BBC loudspeakers (with their dip) for EQ wasn't much of an issue.

S.

 

[Robert]

And what of the none flat and famous BBC dip?

It sounds nice to many people (me included) but moreover it can be explained and replicated at will.

It's a tangible, measurable, audible difference.

 

[Robert]

Indeed Serge, but then it comes down to definitions of transparency. My definition would be an amp that does nothing to the signal apart from amplify it. No amps can pass this test, therefore no amps are totally transparent, and its just down to chosing the flavouring/filtering that I prefer. A subjective choice.

It isn't like that at all.
The final test is always audibility.
There comes a point where distortions/non-linearities, call them what you will, fall below the level of perception. You can only establish this via a controlled listening test, and there have been many.

It goes back to the baked beans.
You cannot taste the difference between two tins of the same type bought from different batches because the differences (and there are always differences) sit below your level of perception.
It shouldn't come as a surprise to learn that food companies use blind testing for such things. There will be a tolerance range for the ingredients and so long as you stay within those, one batch tastes just like another.

Audio is no different.

 

[cooky1257]

It sounds nice to many people (me included) but moreover it can be explained and replicated at will.

It's a tangible, measurable, audible difference.

Oh I like it too-JBL tweak some of their horns in the same way, together with a 0.5dB/oct tilt downwards as per the Floyd Toole research.
So the BBC were tweaking their freq response for subjective reasons-cant for the life of me understand how a very mild mid/ hf dip aids audibility of a 15k pilot tone.

 

[Dik Dolan]

Oh I agree Rob, it does come down to audibility. My point was Serge's use of the word "transparent", where I would use "translucent" instead. Folk saying that amps are to all intents and purposes perfect are where we disagree.

And lots of folk prefer happy shopper beans over Heinz, despite both tins weighing the same, and having pretty much the same ingredients. Small differences do matter to those fussy buggers that notice (or even imagine) that not everything is perfect.

Edit to add: Not all Heinz taste the same either... http://www.telegraph.co.uk/expat/ex...tches-to-UK-recipe-for-Heinz-baked-beans.html

 

[john dolan]

As Robert says The final test is always audibility

But we all have different hearing ability and when i said i could hear the difference with a shunt resistor i'm told by others here i cant but how do they know or can tell how good my hearing is compared to theirs.

The new resistors measure better but who is to say what the level of transparency should be set to when obviously some can hear better than others.

Some can even hear colours change on a monitor.

 

[sergeauckland]

Oh I agree Rob, it does come down to audibility. My point was Serge's use of the word "transparent", where I would use "translucent" instead. Folk saying that amps are to all intents and purposes perfect are where we disagree.
And lots of folk prefer happy shopper beans over Heinz, despite both tins weighing the same, and having pretty much the same ingredients. Small differences do matter to those fussy buggers that notice (or even imagine) that not everything is perfect.

Edit to add: Not all Heinz taste the same either... http://www.telegraph.co.uk/expat/ex...tches-to-UK-recipe-for-Heinz-baked-beans.html

But if an amplifier passes a straight-wire bypass test, then it will be transparent, not translucent, as it's presence can't be detected.

S.

 

[Robert]

Oh I like it too-JBL tweak some of their horns in the same way, together with a 0.5dB/oct tilt downwards as per the Floyd Toole research.
So the BBC were tweaking their freq response for subjective reasons-cant for the life of me understand how a very mild mid/ hf dip aids audibility of a 15k pilot tone.

I think there are two different things going on there.
They added drivers capable of extending past 14khz in order to highlight noise but that isn't related to the famous BBC dip.

The 'dip' is down in the presence range.
Interestingly it isn't present to the same degree on the earlier BBC designs other than the 3/5 and seems to have become a more prominent feature when companies started producing domestic versions of the BBC work.

My understanding is that the dip was introduced to mask the unruly behaviour of the bextrene bass/mid drivers, which due to resonance at the top of their working range could 'shout' and sound hard. So the dip was introduced as a compromise - non-flat response but better subjective result.
Of course the BBC used measurement and blind testing extensively to achieve this subjectively pleasing sound, which is exactly how it should work IMO.

 

[sergeauckland]

Oh I like it too-JBL tweak some of their horns in the same way, together with a 0.5dB/oct tilt downwards as per the Floyd Toole research.
So the BBC were tweaking their freq response for subjective reasons-cant for the life of me understand how a very mild mid/ hf dip aids audibility of a 15k pilot tone.

The BBC created the dip to aid monitoring, to make it easier for the balance engineers to hear what they were doing, not to make it sound better or nicer. By dipping the mid, low HF, it makes the higher HF stand out more. Bear in mind that early BBC loudspeakers didn't go above 15kHz, as the FM transmission system didn't so there's no purpose in monitoring above 15k. When UHF TV started, there was some concern about the amount of 15.6kHz that was being picked up by microphones, and so BBC loudspeakers needed to have more HF response.

S.

 

[sergeauckland]

I think there are two different things going on there.
They added drivers capable of extending past 14khz in order to highlight noise but that isn't related to the famous BBC dip.

The 'dip' is down in the presence range.
Interestingly it isn't present to the same degree on the earlier BBC designs other than the 3/5 and seems to have become a more prominent feature when companies started producing domestic versions of the BBC work.

My understanding is that the dip was introduced to mask the unruly behaviour of the bextrene bass/mid drivers, which due to resonance at the top of their working range could 'shout' and sound hard. So the dip was introduced as a compromise - non-flat response but better subjective result.
Of course the BBC used measurement and blind testing extensively to achieve this subjectively pleasing sound, which is exactly how it should work IMO.

I think you're right that the dip seemed to take on a life of it's own as something desireable when domestic versions started appearing. With all my dealings with the BBC in recent years, the BBC dip never got mentioned, and flat monitoring 'speakers were increasingly being used. PMC and Harbeth mostly.

Interestingly, my B&W 801s had "environmental" controls for the Mid and HF which had a setting to introduce the "BBC" dip if desired. As the 801s didn't use bextrene drivers, they didn't quack in the same way but presumably some studios wanted to replicate the sound they were used to at the BBC.

S.

 

[GTM]

This is an interesting read regarding the above topic (make sure you read it all):

http://www.hydrogenaudio.org/forums/index.php?showtopic=75195

 

[badfink]

This is an interesting read regarding the above topic (make sure you read it all):

http://www.hydrogenaudio.org/forums/index.php?showtopic=75195

Very interesting stuff! Thanks for the link.

 

[sergeauckland]

This is an interesting read regarding the above topic (make sure you read it all):

http://www.hydrogenaudio.org/forums/index.php?showtopic=75195

Very interesting read, thanks for posting it. So really, we're no nearer to knowing why it evolved.

I found the bit about hidden equalisers interesting, as I came across several examples of this sort of thing myself. Producer's desks anyone?

(These were mythical objects that allowed producers to change EQ and dynamics settings by ear. They were seperate from the main desk so the producer didn;t have to keep stretching across the Sound Balance Enginner to make changes. They worked fine, especially as they weren't connected to anything.....)

S.