I used a Denon test CD, very handy piece of kit, a snippet of classical in successive tracks, mastered at 0, -20, -40, -60dB levels. With normal volume levels, the -60dB is completely inaudible at normal listening distance from speakers; so then move up to the speakers, put your ear to the driver, barely discernable sound. Start increasing the volume control, and here of course it varies per the gain of people's preamp, etc - but essentially you will need a volume setting which will blast you out of the room with a normal recording to clearly hear the -60db mastered sound ...
Frank
If the pcb traces you are referring to are for the return currents, these traces should be routed directly under the respective components (if it is not possible to be routed symmetrically around these components).
Routing them away from the components, will risk widening the magnetic loop, a call for interference.
I guess that jneutron has to comment on this.
George
I remember -60dB signal/noise ratio was the magic number in 1970.
Noise of a mastering tape was at this level with no Dolby, and peak modulation at +10. At the high level we were listening in studio, tape's hiss was very audible before and after music, or during pianissimos.
Trying to follow you is always confusing. You said in that circuit you don't see the distortion being amplified as well as the noise. Did you read the original figure 4 it says divide the >AP< reading by 101? And I repeat the 10 Ohm and 1K Ohm resistors have no effect on the measurement. The circuit woks fine AC as well as DC for audio frequencies (certainly 1K). I quit on this, still waiting for the feedback going round and round.
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Indeed: Like worrying for rms or peak value influence of pure silence !!! ( -110 or –134db)
"Now the interesting issue is how we perceive signals. "(LOL)
Where? I really am being concerned about you. You either are confusing issues or posts. The issue was resistor noise in the first presentation in BP's column. You were the one that kept mentioning resistor distortion. I asked you about the circuit node values to be sure we were on the same page. Somehow you seemed to derive all sorts of nonsense from this
I thought I made it clear we were talking about the entire measurement system and you keep going back to two resistors. I deliberately tried not to provoke you when you ignored the importance of phase in the input impedence.
So Scott I really am concerned with how you are responding.
ES
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oh no, not an engineering trade off - can't I have it all?
If the pcb traces you are referring to are for the return currents, these traces should be routed directly under the respective components (if it is not possible to be routed symmetrically around these components).
Routing them away from the components, will risk widening the magnetic loop, a call for interference.
I guess that jneutron has to comment on this.
George
Caution here Ed.
Transforming single isolated results into a hypothesis (“if you believe”) and bringing it into auditory perception area, may lead to erroneous conclusions.
http://www.diyaudio.com/forums/analog-line-level/146693-john-curls-blowtorch-preamplifier-part-ii-3108.html#post3275314
But I’ll hit Scott’s nerves (feedback
) pointing to the long tested practice: Noise masks low level signal details. At the same time there is a statistical -alas conditional - possibility for noise to mask low level distortion as well.
Lowering noise brings out low level signal details . Concurrently, the conditional masking of distortion by noise becomes even more conditional.
George
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You are the second person to make this comment so I'll make a mental note of it but I can't quite relate this to my experience.
I think distortion can be reduced by lowering the impedance of the system by using a lower impedance pot to control the LDRs but this will also, in theory, reduce their lifetime.
If I ever work with them again - I have some in my box - I will try different impedances to see if this character changes.
But I’ll hit Scott’s nerves (feedback
Noise masks low level signal details. At the same time there is a statistical -alas conditional - possibility for noise to mask low level distortion as well.
Lowering noise brings out low level signal details .
George
George, this is one of the reasons why signal sources with lower resolution and higher noise of any kind (vinyl, tape) and audio components with higher noises are often highly regarded in subjective evaluation. The sources with lower resolution and higher noise are easier and not so demanding on quality of the rest of the audio chain.
George, your numbers (-100db) seems overkill.
There are several effects at work, witch reduce our ability to hear distortion. And it is happy for the loudspeakers business.
Noise can cover-them with the band-masking effect. But different sensibility of ears to frequencies and their levels (Fletcher & Mudson) helps too: Our ears will be a lot more sensible to harmonics situated at 3KHz than at 40 or 10KHz, at low level.
On the opposite, our culture (cf pretended Curl's ability) can help to focus on them.
Our ears are able to explore 120dbs, but it is an adaptive process, i believe more that, at a given average listened level, 30db is more realistic, and our ears need a little time to recover their low level listening ability. Like our eyes to light.
It is easy to play with a generator and synchronous frequency multipliers to figure out how much you need to add a 2X or 3X signal, before you can hear a change. (A lot).
All sound engineers knows how it is difficult to separate two voices singing the same part. Even when it is a male plus a female ones.
I believe, on my side, our ears are sensible to the dynamic behavior of a signal more than the harmonic composition of it. Slew rate is one of the keys.
About those resistances distortion measurements, for me, it is a demonstration by absurd that the tested resistances do not produce any audible distortion, and the tested OPA neither.
We need the same measurements with other kind of resistances, all along with blind tests, to figure out if other brands matters or not.
We definitively need more scientific exploration of those distortion phenomenas, with blind tests, to can correlate forever measurements to real life effects, but the paper you refer-to shows how it is difficult.
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True and thanks for adding this.
As your words may start a debate –something you didn’t intent- let me say something that will direct this possible debate toward me instead.
That I an amateur, who is in the favourable position to cater for his home reproduction equipment and not for others -unknown customers- is known.
That I enjoyably listen to vinyl, cassette and FM radio signal sources which have low S/N ratio (and I wouldn’t say low resolution) is something that I have written.
What may come as a surprise to some, is that I keep the same attitude (don’t matter much about S/N ratio) toward digital signal sources too. The justification is that the same aural perceptual patterns apply there.
Yes, it may sound schizophrenic to disregard their inherent superior S/N technical capabilities, but disregarding is not the intend. It is the speech or music I am interested in listening to and these are all transfers from the analogue recording era. Thus the S/N ratio embedded in the recorded sound is inevitably -and by far- the dominating factor even with my CD source.
Had I have the tendency for technically (specs) better and modern original recordings, I still would put emphasis on low distortion rather than low -uncorrelated- noise in my reproduction chain.
George
Iv'e also noticed that some audio designers sometimes prefer to choose a higher noise option within their circuits - perhaps because it adds some "feeling of excitment" or perhaps because it masks some other less benign sounding noise.
I have noticed both of these effects in my own design work but personally I always aim to reduce all forms of noise from whatever source.
Christophe
I agree to the iota on what you wrote.
The “ –100db is overkill” needs some answer. (for my daily praxis and reasoning, see my last post).
Under favourable conditions (music material and equipment), the 3KHz –5KHz approx. range is where we are able to notice problems deep down in level. This is supported by contemporary research but even the old Fletcher curve (attachment from L. Beranek 1949) provides a hint.
George
Attachments
Look at the THD curve for a 10mV signal. According to the data sheet there is a lot more distortion at that level. Would you hear that or is it all noise? Then look at the distortion level for 10 volts out into 600 ohms would a pro system see those levels and what would it sound like?
Distortion is not a fixed number.
Distortion is not a fixed number.
George, i'm happy to see most of us have the same references and way to think.
About this -100dB, my point was, even if we could hear some -80db 3KHz harmonic alone, played at 30dB spl, ie at the acoustic noise floor of our very quiet listening room, i doubt our ears is able to event feel its existence when played in the same time than the 110db spl fundamental, when you wife scream: "George, decrease the volume, all the neighbors complain !" and you just see his lips moving
And, if you decrease the volume, as she expects, the same distortion will be well under the minimal sensitivity of our ears, and noise level of your room. Right ?
About this -100dB, my point was, even if we could hear some -80db 3KHz harmonic alone, played at 30dB spl, ie at the acoustic noise floor of our very quiet listening room, i doubt our ears is able to event feel its existence when played in the same time than the 110db spl fundamental, when you wife scream: "George, decrease the volume, all the neighbors complain !" and you just see his lips moving
And, if you decrease the volume, as she expects, the same distortion will be well under the minimal sensitivity of our ears, and noise level of your room. Right ?
We'll never know.
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