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Old 17th June 2010, 02:08 PM   #1
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Default Pre amp response to minimum signals

I see data of preamps referring to max. level at input and output, but what about the smallest levels of a musical signal coming in and out.
I know that the smallest level of actual music signal that can be retrieved is relative to the system noise floor, but as a test and measurement example:
Say that signal levels of 10 uA@ 10 mV are presented at the actual physical connector and or switch, and that the the pre amp is capable of transferring or responding to that level.
Is this considered to be good low level resolution or are their figures better than this with examples of such pre amp designs.
What should the specs of a well designed pre amp be regarding low level quality signal reproduction?

Last edited by philmagnotta; 17th June 2010 at 02:11 PM.
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Old 17th June 2010, 03:08 PM   #2
SY is offline SY  United States
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Interestingly, you can often hear signals below the noise floor.

Analog circuits rarely have a "resolution" limit except in the imaginations of magazine writers, it's more a matter of how deep below the noise floor before you can't hear things. Digital circuits have resolution limits, but the whole purpose of dither is to circumvent that- which it does.
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Old 17th June 2010, 03:53 PM   #3
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Interestingly, you can often hear signals below the noise floor.

Analog circuits rarely have a "resolution" limit except in the imaginations of magazine writers, it's more a matter of how deep below the noise floor before you can't hear things. Digital circuits have resolution limits, but the whole purpose of dither is to circumvent that- which it does.
Yes, I do understand about ability to hear music signal within noise as in tape systems, vinyl, etc.
As for analog rarely having resolution limits. I think I see what you mean, but even if the noise floor were lets say even -150 dB below a micro-volt!!, what type of quality can we theoretically expect.
I mean, we are limited to the lowest level of the recording or transmission of source.
So, from my experience, musical signal levels of say minus 80 dB below 0 (0dB referred to .775 volts) are practically speaking, about at the limits depending, of course, on the level of monitoring and the total system noise right on through to the monitors.
I was just wondering on the actual quality of such signals, noise not withstanding, and what type of manufacture of pre amps behave well in this regard.
Specifically about the technical descriptions given at IRD Audio's LLC-P Purest pre amp page, Quoted in part:
... "To maintain short signal paths with a minimum of wires special relays are used for audio signal switching. High tech telecommunications relays from Japan have been selected for the job. All contacts are gold clad silver and signal levels as low as 10 uA@ 10 mV are easily accommodated for superb low level music detail."
Without getting into the gold-clad silver construction, I am curious about the 10 uA @ 10 mV wording.
What does this mean in practical terms please?
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Old 17th June 2010, 07:00 PM   #4
jcx is online now jcx  United States
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search for: Shannon Hartley Channel Capacity Theorem

in short there is a limit on information rate (in bits per second) that can be conveyed by a finite bandwidth Analog channel with additive noise

"hearing below the noise floor" is bandied about rather loosely in audiophile circles - usually people haven't adopted a sophisticated enough view - you need to include frequency dependence of "the noise" and some properties of our auditory system

auditory critical bands are measures of how far in frequency signals or noise have to be separated to be perceived simultaneously

there are some interesting correlation "unmasking" phenomena but I haven't seen papers showing that the effects really reach below the accepted frequency dependent hearing noise floor - which is only reached after minutes of accommodation in total silence - not the level we usually encounter in music venues

then you need to learn about thermal noise in resistors and shot noise in electronic amplifiers - there is no possibility of detecting/recording "-150 dB below a micro-volt" at room temperature, audio bandwidth

really extreme, expensive electronics could maybe give ~140 dB S/N over the audio band but would require Watts power dissipation in feedback resistors (assume signal electronics could use 10 rms max signal vs 1nV/sqrt(Hz)*sqrt(20KHz), ~ 50 Ohm max resistance)

once you have the electronics then you simply can't transduce audio sound levels into electrical signal at that dynamic range - microphones and their preamps are much noisier
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Old 17th June 2010, 07:06 PM   #5
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Phil: First, stop trying to make sense out of high end audio marketing literature. Apply a little Ohm's Law to that meaningless bit of brochure-speak

Second, let's make sure you understand the distinction between dynamic range and resolution, two different things which you're conflating. "Resolution" has just as much meaning between (say) 1.00000V and 1.00001V as it does between 0.00000V and 0.00001V.
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Old 17th June 2010, 07:51 PM   #6
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Resolution and detail depend mostly on how carefully you are willing to listen to a system. And since your willingness to listen carefully more often than not depends on how well you like the sound of the system, you might say that detail and resolution are dependent more on distortion levels than noise floor issues, both for psycho-acoustic as well as technical reasons.

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Old 17th June 2010, 08:39 PM   #7
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Phil: First, stop trying to make sense out of high end audio marketing literature. Apply a little Ohm's Law to that meaningless bit of brochure-speak

Second, let's make sure you understand the distinction between dynamic range and resolution, two different things which you're conflating. "Resolution" has just as much meaning between (say) 1.00000V and 1.00001V as it does between 0.00000V and 0.00001V.
Ok SY, I'm trying.
Lets see. Dynamic range as understood by me, a violinist:
The least or absolutely quietest qualified note signal that can be distinguished as useful over that, which is purely bow noise at one end, and the range or amount of output power in musically acceptable terms representing the limit at which the instrument will begin to go no further by producing more noise than useful tone... Instruments dynamic range.

Resolution. the ability of the hearer or musician and the instrument to produce the smallest difference of level in output, (plus or minus) while also considering those level differences at various starting levels, such as resolution near the top extremities where the ability to produce differences is running out of head room, differences at the lowest extremes where resolution suffers from the same constraints as the former.

About the meaningless brochure-speak.
I can't say, so I'll take your word on it for now.
I believe that I did not make my self clear originally.

Also, jcx and jlsem brought out useful replies as well, and I do mostly understand their replies.

Let me ask in a different way.
Given a quality pre amp, in my terms, would mean that low level resolution would be at some level just above any distractions from noise and distortion.
At this condition does the response to the slightest dynamic, as well, any other useful measurement and listening quality - in that lowest range - have a different behavior when compared to the same conditions of dynamics/resolution when near the top of the pre amps range?
In other words, are these conditions - performance near the bottom scale versus the top end, characteristically different?
I would think so because they are all subject to basic laws of constraints.

As pointed out from jslem, it also depends on the listener, their resolution in hearing, their commitment towards that goal musicologically, etc.
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Old 17th June 2010, 08:56 PM   #8
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Your question is a fair one, Phil, but we don't have easy measurements to give it a spec.
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Old 17th June 2010, 09:25 PM   #9
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Your question is a fair one, Phil, but we don't have easy measurements to give it a spec.
Hi John:

You have a well documented history as a designer of quality audio devices.
I was really hoping for more comment on this matter, if you please.
About easy measurements:
Well do you have any experience with difficult measurements?
It's possible that some may not agree with what I will say, but even in audio electronics engineering, sometimes referred to a mastered and mature discipline, I see that we are not finished yet.
I 100% believe that new approaches, both in measurement and defining what a system should do and feature are not fully explored.

In simple terms, the dynamic behavior of a spring or speaker when subject to various applicable signals at small signal versus large, are not proportional.
This is what I am asking.
What type or make or pre amp is close to this ideal and or what should one look for - besides hearing - in design philosophy?
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Old 17th June 2010, 09:36 PM   #10
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The problem is indeed definition- once you define what you mean, you can measure it. The problem is that "resolution" is tossed around colloquially. Let me give some quantitative examples:

Put 1V of DC into a circuit. You get 1V out. Put 1.000001V in. Does the output move? Is it distinguishable from the 1V case?

Put 1V at 1kHz into a circuit. You get 1V out. Put 1.000001V in. Does the output move? Is it distinguishable from the 1V case?

Put 1V of pink noise into a circuit. You get 1V out. Put 1.000001V in. Does the output move? Is it distinguishable from the 1V case?

Put 1V at 1kHz into a circuit at the same time that you have 1V of pink noise. You get 1V out. Put 1.000001V of 1kHz in. Does the output move? Is it distinguishable from the 1V case?

Four different definitions, four different measurements (all do-able), probably four different results.
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