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General debate thread about audio measurements

pkane

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I am saying that a nonlinear transfer function generates intermodulation distortion when applied to complex signals - not harmonic distortion. For sure, you can have any transfer function you want using DSP, but it won't be meaningful when applied to a complex signal.

Can you please explain why a physical device with a non-linear transfer function does not produce the same intermodulation effects? And if I can simulate the same transfer function as some physical device in DSP, why would this not be meaningful?
 

Cosmik

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Can you please explain why a physical device with a non-linear transfer function does not produce the same intermodulation effects? And if I can simulate the same transfer function as some physical device in DSP, why would this not be meaningful?
A physical device would be identical to the DSP and vice versa. But neither DSP nor the physical device would be generating harmonic distortion when applied to a complex signal.

The idea that a valve "generates second harmonic distortion" is only true for very simple, single tones. Put real music into it and you get garbage. As I said in my previous comment, if you choose your recordings carefully, then maybe the distortion might add some 'edge' to simple music. But put in a symphony orchestra and you are reminded of the character of those old valve radios with paper speakers or 78 records.
 

pkane

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A physical device would be identical to the DSP and vice versa. But neither DSP nor the physical device would be generating harmonic distortion when applied to a complex signal.

The idea that a valve "generates second harmonic distortion" is only true for very simple, single tones. Put real music into it and you get garbage. As I said in my previous comment, if you choose your recordings carefully, then maybe the distortion might add some 'edge' to simple music. But put in a symphony orchestra and you are reminded of the character of those old valve radios with paper speakers or 78 records.

Got it, and fully agree. I've been thinking about a generalized DSP distortion toolbox, something that would let me mix and apply various types and levels of distortion. An adjustable non-linear transfer function was one of the main components planned :)
 

Cosmik

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Got it, and fully agree. I've been thinking about a generalized DSP distortion toolbox, something that would let me mix and apply various types and levels of distortion. An adjustable non-linear transfer function was one of the main components planned :)
Well, best of luck with it, but personally I think you should be putting your efforts into eliminating distortion! :)
 

andreasmaaan

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Got it, and fully agree. I've been thinking about a generalized DSP distortion toolbox, something that would let me mix and apply various types and levels of distortion. An adjustable non-linear transfer function was one of the main components planned :)

@pkane I'm very interested in what you're doing, as controlled distortion is something that is impossible with all the consumer DSPs I'm aware of, and what you're doing is something I've been meaning to try for some time but have never got around too (big learning curve for me in terms of maths and programming).

Would you be so kind as to share with me whatever you come up with? :)
 

pkane

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@pkane I'm very interested in what you're doing, as controlled distortion is something that is impossible with all the consumer DSPs I'm aware of, and what you're doing is something I've been meaning to try for some time but have never got around too (big learning curve for me in terms of maths and programming).

Would you be so kind as to share with me whatever you come up with? :)

Of course. At the moment it's just in the planning stages -- too many audio projects started and not completed as is :)
 

andreasmaaan

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Of course. At the moment it's just in the planning stages -- too many audio projects started and not completed as is :)

Exactly the state I'm in :)

Anyway, awesome - thanks!
 

amirm

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I think the point that harmonic distortion is not just the clear effect we see in sine waves was worth mentioning. With any real music we will have a spray of such distortions for every fundamental frequency. In my listening tests I find that this spray will then hide low level detail. The effect is not what people describe in tonal response changing.

I find the effect mostly when bass notes come in. Due to their high amplitude and ample bandwidth for harmonic distortion to materialize, it is easier to hear the loss of detail that way.

Now this is not solid, controlled listening test results. :) But it is what I observe at modest levels of THD.
 

RayDunzl

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With any real music we will have a spray of such distortions for every fundamental frequency.

I can measure harmonic distortion coming from the speakers.

The relative levels are quite dependent on the level of the fundamental, and the harmonics rise more rapidly than the fundamental as the volume level is increased.

Do electronics increase their distortion proportionally more rapidly than the fundamental (at normal rising signal levels), or is there a more fixed relationship?

Is there even enough electrical harmonic distortion to matter?
 
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amirm

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Is there even enough harmonic distortion there to matter?
WIth headphone amplifiers, yes. I can easily push them to single digital THD numbers by just turning up the volume.
 

RayDunzl

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I can easily push them

Is that at "normal" or "too loud" levels?

(I realize things go wrong when you run out of steam)
 

NorthSky

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How much distortion a volume knob from a high grade preamplifier adds to the music playing when you move that knob and leave it where the volume level sounds right?

The volume pot, how much importance should we give? ...Balanced dual L & R separate volume controls.
_____

WD-Stereoknight-angle.jpg


http://witchdoctor.co.nz/index.php/...ne-balance-transformer-volume-control-review/
 
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maverickronin

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Is that at "normal" or "too loud" levels?

(I realize things go wrong when you run out of steam)

It really depends on the headphones. Impedances and efficiencies are all over the map. Impedance can be from single digit speaker territory to peaks above 1200 ohms. Efficiencies I know of range from ~76dB/mW to greater than 120dBmW.

"Too loud" with one headphone can easily be completely inaudible with another.
 

amirm

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Is that at "normal" or "too loud" levels?

(I realize things go wrong when you run out of steam)
For mild levels of distortion, no. But for the extreme THD with high power amps, I can only do it for a 5 seconds or so before worrying about my hearing. :D

In general, headphone amps run out of power far more easily than speaker amplifiers. Part of it is due to very high impedance of some headphones which reduces the power substantially.
 

amirm

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How much distortion a volume knob from a high grade preamplifier adds to the music playing when you move that knob and leave it where the volume level sounds right?
Do you mean with passive or active pre-amp Bob?
 

NorthSky

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Nothing specific Amir, just an overall volume pot we all have on our preamps, integrated amps, receivers, headphone volume control from headphone amps, laptops, tablets, etc.

Some I bet are cleaner, introducing less noise, distortion. That was my main point.
The picture and the link are just an example. When I was searching for a high end volume pot, I had a different one in mind, one that you posted in the past, and expensive too, very, this one ($1,000) came up in that search, and I found it pretty, simple, nicely built, relatively down-to-earth priced. ...But without any more than that.

Is active preamp better than passive?
 

Sal1950

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