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Old 16th August 2014, 03:01 PM   #1
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Default Voicing an amplifier: general discussion

I've been thinking quite a bit about how to characterize the sound capability of an amplifier and or audio playback system and I've come up with three main categories:

1. soundstaging
2. timbral accuracy
3. PRAT

Now, before any of you jump in with any of the other numerous adjectives that can be used to define the elements of sound, I will tell you why I think these will fall under the three main descriptions above and more importantly, how they correspond to electrical design decisions. Let's set aside the discussion of the interrelationship of all three for the time being and see if the treatise presented below is valid or useful in any way to anyone trying to voice their audio to their taste.

Soundstaging is a product of level accuracy and dynamics. Voices and instruments are placed in the soundscape by their levels and the persistence of this image is mostly a product of dynamic accuracy. I considered that the coherence of the soundstage is also dependent on the PRAT but as I said before, I am trying to start with a simpler taxonomy as the basis for something more comprehensive later.

Timbral accuracy was the easiest in my mind to identify. It is the frequency response reproduced with the most accurate tonal spectrum. Easy to conceptualize, less easy to produce in practice.

PRAT (pace, rhythm and timing) is mostly a function of the slew or speed of the amp. In the CFA vs. VFA rumble thread, I suggested that the greatest slew rate does not necessarily provide the most accurate PRAT so going balls out for amp speed may result in unintended sound artifacts which may or may not be pleasant.

Okay, I'm now ready for the slings and arrows. Have I nailed it or is my simplified characterization only useful to simpletons?
 
Old 16th August 2014, 03:56 PM   #2
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Well first you need to come up with some real world examples of amps that have any of those qualities for the good or the bad.
Except for amps that have obvious euphonic coloration it might be hard to identify any accurate amps with those qualities.
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Old 16th August 2014, 04:25 PM   #3
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Wouldn't you need to use speakers that are correctly voiced in the first place? Which ones? I can hear the can of worms opening...
 
Old 16th August 2014, 04:51 PM   #4
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I can tell you how I do it, others may disagree. Electronics are a no-brainer. If the electronic system frequency response is flat, say -3 dB at 5 and 30 kHz, the distortion is low, say under 0.01% over the same range, and the amp has enough current to do the job with whatever speakers are in use, the job is done. You can do better than those numbers, but they're in the ballpark. Anything meeting those criteria will be near indistinguishable. If the load is really screwy you might need to look at stability. If you're doing vinyl the preamp performance needs to be up to snuff as well.

The rest is transducers. What's the input source, how is the speaker designed and voiced and how is the room arranged and treated. That's where the real bang for the buck is.
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Old 16th August 2014, 05:57 PM   #5
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Thanks all for the enthusiastic opening of this thread. Ideally, I'd like the discussion to center around amp design decisions that emphasize the three sonic qualities described above but only if we can agree those three qualities are comprehensive descriptions of what we are trying to achieve in sound reproduction. In other words, is there any other sonic attribute that I didn't include or that doesn't fall under one of those three categories?

Conrad Hoffman
When you make your amps, assign the percentage of emphasis you place on the sonic result using those categories such as:
soundstage: 40%
timbral accuracy: 40%
PRAT: 20%
Your build description gives the impression that you aren't afraid of applying negative feedback and the resulting higher harmonics as long as you can get the THD within the range you want. Have I assessed you properly?

hongm
You're right, it is an audio system and all components interact but I'd like the focus on the amp alone for now.

Speedskater
I guess that couldn't hurt. Let's use two popular diy amps as an example. I have a myRefC and a battery powered gainclone which I use with Vandersteen model 3 speakers directly with the LAME digital content on my Toshiba player. Their sonic character to me:

Gainclone
soundstage 28%
timbral accuracy 31%
PRAT 19%

myRefC
soundstage 33%
timbral accuracy 38%
PRAT 17%

I will rate an old big block Threshhold by comparison:
soundstage 14%
timbral accuracy 38%
PRAT 18%

Last edited by yldouright; 16th August 2014 at 06:02 PM. Reason: layout
 
Old 16th August 2014, 06:16 PM   #6
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Also, you assigned these percentages purely based on subjectivity, and that is going to be a problem. It's not like any of these ratings are calculated using a ratio of some sort. You have too many variables such as the quality of the recording, your playback source, the quality of your DAC, and the accuracy of your speakers. As you can see from the forum threads, any of these factors can trigger a huge debate.
 
Old 16th August 2014, 06:32 PM   #7
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hongrn
Okay, let's assume a distortion analyzer/FFT can show us timbral accuracy and slew shows us PRAT. I don't necessarily agree that they automatically do but I accept they point us closer to the goal. What measures soundstage? Is it even a real attribute if it can't be measured? I hope you see why you can't completely remove subjectivity from preferences but that shouldn't stop us from exploring the practices that can achieve those preferred attributes.
 
Old 16th August 2014, 07:09 PM   #8
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Well, my amps don't have sonic properties when compared to other well designed amplifiers. I'm not afraid of negative feedback, in fact I think Harold Black was a pretty smart dude. What I've found is that if an amplifier sounds different from others, be it extra good or just bad, there's something wrong with it. Sometimes it's something obvious, found with the usual measurements on the test bench. Sometimes it's something subtle like RF getting in or a slight oscillation at certain amplitudes or with certain loads. Eliminate the design blunders and you eliminate the audiophile tonal descriptions.
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Old 16th August 2014, 07:25 PM   #9
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Quote:
Originally Posted by yldouright View Post
hongrn
Okay, let's assume a distortion analyzer/FFT can show us timbral accuracy and slew shows us PRAT. I don't necessarily agree that they automatically do but I accept they point us closer to the goal. What measures soundstage? Is it even a real attribute if it can't be measured? I hope you see why you can't completely remove subjectivity from preferences but that shouldn't stop us from exploring the practices that can achieve those preferred attributes.
It is difficult to have any meaningful discussion before terms are defined and agreed.

Timbral accuracy? WTF is that? Do you mean frequency response? Precious!

PRAT? I could say a lot more, but I will refrain.

Soundstage? An illusion depending on where things are panned by the mixing desk. Great fun but no more.

Voicing! Pretentious nonsense, unless you are dealing with a physical acoustic device like a cello or a loudspeaker.

Last edited by cliffforrest; 16th August 2014 at 07:26 PM. Reason: I canna spell
 
Old 16th August 2014, 07:29 PM   #10
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cliffforest
Welcome to my thread and please, don't hold back
I believe I explained timbral accuracy and it is more than just frequency response, it is the ability to reproduce a waterfall plot of mulitiple simultaneous frequencies. When you hear a trumpet play a note, it is not playing only that frequency. A soundstage very well may be an illusion but it is curious that many people in a room can identify the same location of a sound when an amp is capable of creating one. Not being able to measure it does not mean we give up identifying what creates one.

Conrad Hoffman
There are numerous examples of amps with poor or mediocre THD numbers that sound really good and have some of those three attributes. One has to look no further than Class A amps to verify this. I'm sure you're not suggesting that amps that introduce any of the three qualities above into your audio system are faulty by their excellence but it is curious that you wouldn't strive to achieve those qualities in your designs. What parts do you typically use to build your amps?

Last edited by yldouright; 16th August 2014 at 07:39 PM.
 

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