Primera visita a una tienda y lo 1º que me dicen es que magnat y berhinger es 1mierda

Sobre la audibilidad d ela THD e IMD quizás también os puede interesar esto:

Originally posted by smellygas


Woh, these were some very interesting papers from Geddes. Thanks for the link! I don't fully understand the math, but he basically showed that there is only a very weak correlation between IMD/THD and listener perception. He didn't include the actual % or dB levels of distortion, which makes it difficult for me to interpret. However, what this likely means is that simple measurement of IMD or THD levels does NOT correlate very well with audible problems with the sound. He does, however, create his own composite formula for quanitfying the amount of distortion present (not strictly HD or IMD) that correlates VERY well with listener preference (we're talking R^2 of 0.9). This tells me that increasing distortion is definitely objectionable, but increasing HD or IMD does NOT necessariliy correlate with objectioable sound. Maybe someone else can interpret the article better than me. Interesting.

SG

Gedlee:

Let me interpret since I did the work. The "weak correlation" of THD and IMD to perception was NEGATIVE - you forgot to mention that. This means that, as a metric of perception, one should increase the THD to make it sound better. This is of course absurd, but it's the absurdity of THD and IMD measures that is the culprit not the results of the test.

The THD and IMD numbers are indeed shown in all the graphs. They are the X-axis.

Its NOT the level of the harmonics that matter but where the nonlinearity occurs - at low levels or high levels and the order, 2nd, sixth, etc. Low level nonlinearity is by far the most insidious especially if high order - like crossover distortion in an amp. This is why an amp with extremely low levels of THD can still sound terrible. But loudspeakers, on the other hand, tend to have nonlinearities that increase with level and are likely very low level like second or third. This makes them fairly benign. In fact, for the most part, nonlinearity in a loudspeaker (as long as its not broke) is a non-issue. In a test of compression drivers we had twenty five people evaluate distortion levels up to 25% and statistically noone could detect it at those levels.

Its hard to make blanket statements about the audibility of nonlinearities in specific cases, but for the most part nonlinearity is a major concern in electronics, but so much so in loudspeakers.
There are, of course, going to be exceptions to this.

How much tweeter distortion is audible? - diyAudio


Este otro:

Geddes:

Actually modeling the nonlinearity curve is the only way to do this. Thats because THD and IMD are only symptoms of the problem which occur when precise waveforms are used. To hear the effects of these same nonlinearities on an actual music waveform you have to model the underlying root caues nonlinearity. Thats what my MathCAD program does. You can use any wave file. Lets decide on an example wav file and nonlinear characteristic and I'll post the results. First would obviously be a strong third order soft clip, because you will be amazed that at 50% THD the effect is completely inaudible. Then a .1% example of crossover distortion which will sound terrible.

http://www.diyaudio.com/forums/multi...audible-2.html





-Éste que mola más:

Gedlee:

THD on a compression driver was measured at 25% and it was not audible when compared to the direct fed signal. Compression drivers ARE NOT low THD devices.

The Summa speakers are not PA monitors, they have almost never been used for that purpose (although they do work quite well). They are almost exclusivley used for Stereo and HT critical listening. They were designed to be audiophile loudspeakers not Pro loudspeakers. I use Pro drivers because they are better drivers.

My point is that I don't care about nonlinear distortion anymore. I don't study it, I don't measure it and I don't look at THD levels in the drivers. Low THD, high THD, it doesn't matter. What matters is polar response, low diffraction and thermal capability. Smooth response is desirable, but ruler flat on any one axis is also irrelavent. THD and IMD are meaningless.

So did I or will I do the tests that you suggest - no. If you want to "prove the validity of THD" then you do it. I'm simply not interested. I did enough tests to make up my mind and if I have not convinced others then so be it. Let them think what they will. I made my case and I'll rest on the evidence presented.

And I am not the only one of this opinion - there is Floyd Toole, Laurie Fincham, Alex Voishvillo and many many other people who spent their lives looking at sound quality.

O este otro también bastante interesante:

Audibility of Non-Linear Distortion: A Practicum


I'm a real measurements person, but I like to keep things practical. After looking at enough graphs of harmonic distortion for different drivers, I decided to try a simple experiment - can I actually hear a 5th harmonic at -xxdB down from the fundamental?

I devised a relatively simple method of doing this. Using a digital audio 'workstation' (Cocko's Reaper), I set up a series of pitch shifters, one each producing a 2nd, 3rd, 4th, 5th and 7th harmonic. I patched in a stereo input (from my CD player), and also sent out the unprocessed 'fundamental'. I then patched everything out on one channel to my amplifier. I checked that the results with a FFT and a microphone, to make sure I was on target for my harmonics.

I also created an 'IMD' test, but taking two pitch shifters, and setting their output to +15% and -15% of the fundamental frequency. For a single tone, this produces a warble tone, often used in speaker testing. Watching a FFT of the output of a speaker, it was obvious this induces a lot of IMD.

Here is a screenshot of my setup:




So using the volume control on the various harmonics/IMD tracks, and the 'solo' buttons, I could listen to specific levels of each harmonic/IMD. The volume slider lets you set a specific -dB relative to the fundamental/source signal.

The results were surprising. Here is a chart of the point where I could no longer hear a difference between just the original, and the original plus the harmonic/IMD:




All listening was done on a single Pluto loudspeaker, my head 18" from the speaker, at a 90dB SPL level.

The warble tone was of a 100Hz sine wave. All other tests were done with music. I can provide reference to the specific albums if people really want.

A few things were surprising - the biggest was that with music, for the most part, I couldn't hear differences below -40dB down. Particularly with the IMD test, which was particularly noxious at high levels, below -30dB, it was basically inaudible.

I noticed that music with lot of HF content made it easier to hear (Vivaldi). Music with lots of bass, and/or lots of compression made is harder to hear differences (Nujabes). Contrary to 'common knowledge', complex music (orchestral) masked differences while simple (singer/acoustic guitar) made it easier to hear differences. So the point at which difference could be heard changed depending on the music, but still within what I would call a small window- ie, somewhere between -30 and -40dB.

I've zipped up the file I made to do these sort of examinations, so other people can try it. Reaper can be downloaded for free, and then use the file I've attached. People will have to route their hardware I/O (on each track), but other than that, it should be relatively straightforward. Use the solo button of the harmonics/imd to turn them on or off. Keep the 'fundamental' solo on. Change the level of the harmonics/imd with the track's respective volume sliders. Don't change the level of the track labeled 'fundamental'. To change the volume of the IMD tracks, use the volume slider and solo button of 'IMD1' - 'IMD2' is slaved to it. Be careful where you click, you may disrupt some of the internal routing.

Feedback? I, for one, am less worried about non-linear distortion now.

Audibility of Non-Linear Distortion: A Practicum - diyAudio


Y es que todos van en la misma línea... no me extraña que suenen tan bien las Supreme 100 a SPL medio tras la EQ con su respuesta polar impecable, verdad juluska!?


Un saludete