Distortions

Distortion or not my nosDAC sounds dam good.

 

Indeed!

 

Hi,

Nope, I said that in order to work as intended three conditions need to be met.

1) The I/V resistors and the reference resistors need to be of a value correct for a "bogey" chip at the supply voltage used.

2) The I/V resistors must then be adjusted to either give a "safe" value which will never clip even with a chip having the highest full scale current which will lead to a 3db difference in output level between the highest possible full scale current and the lowest, or the I/V resistors must be matched to the actual DAC's full scale currents in order to maximise the dynamic range. In other Riv = (Vdd-3V)/Ifs where I fs is the actual full scale current of the TDA1543 in question.

3) The reference resistor must be adjusted such that the distortion is minimised, is a suitable analyser is available. That failing it is neccesary to establish a quiescent voltage on the output of (Vdd-3V)/2+1.8V as the best that can be done without an analyser. A quick crosscheck on the 'scope should show no clipping with a 1KHz 0dbfs sinewave.

Ciao T

 

stuart - i'd picked up on the three options as well - be interesting to see if they are remedy or potential tweakery.

t.bone - gotta say - as with you i love the NOS - and thats with inherent fault of my unit! cant wait to hear it when fixed, run in (have you noticed improvements in yours over time - subjective i know but gotta ask) and adequately powered (i have asked Derek for the details on his PSU) and it'll all be on a dedicated ring main when we move in 4 weeks

and finally - FWIW - i think 'distortion' is possibly better as its own thread as it could run on a bit

 

Hi 3D Sonics


[[ Not at all, my argument is -60db 2nd harmonics (or 0.1% THD at digital full scale ) that is monotonic falling with level is a sonically very harmless form of distortion. Haveing 1/100's of that mount of high order distortion is much more objectionzble.]]

For me any distortion is objectionable . Only if can't get rid of the distortion,
you must choose between the one that you find less objectionable.Is like to choose between two fatal diseases.


[[ I am not arguing that everything sounds the same, but that distortion must be considered in the cointext of audibility. You complain over "high distortion" without qualifying and considering the impact. That is just plain idiotic.]]

Idiotic is pretending that any distortion isn't objectionable and may be even desirable (for to add some warm...?) , or a thing , not to care about.


[[ Well, they do? Aer you quite sure about that? I mean not just parroting others, but have you actually done extensive experiments (or at thge very least anbalysed the actual circuitry inside the DAC and attempted to understand it? ]]

Who is parroting others, are the ones that are manufacturing dacs with the TDA1543 , without even looking to the data sheet.
In 1984 I began to try passive resistor I/V in my now defunct Philips CD 100 .
IF the resistor that performed the I/V become greater that 47 Ohms one semisinusoide becomes grater than the other (even by eyes ).
The only way to do the passive approach , is with a transformer that maintain a low voltage excursion (low impedance) at the output pin of the DAC , but of course the transformer will introduce others problems.




[[ I am not saying that. However, if you use a low efficiency moving coil speaker and drive it from a voltage source you are establishing the exact conditions to maximise distortion and compression. That is a simple fact. ]]

In a current drive speaker you made a trade of. You get more excursion linearity , but less timming and fidelity to the original signal waveform.
If you measure the voltage at the therminals of the speaker , you will see that this voltage represents much of the motional voltage (the voltage produced by the effective movement of the voice coil speaker ).
In the resonant frequencies you will have a much greater voltage , that show that the speaker at that frequencies are running without any control and as you must know , a ressonance in the frequency domain is equivalent to a prolongment in time , in the time domain.



[[ Draw your own conclusions. And occasionally supplement parroting plainly false statemenst with actual empirical work. You may find the results rewarding.]]

I don't know your experience ,and even don't care , but I'm in Audio for more than 35 years and I never pretend to be right because of that.
And in this discussion , is you that must give the proof , because you are saying that a speaker must be current operated and this is against the rules that much clever people ,before us , ( P. Walker, Baxxandal, Hafler,....and much more )
The faith can't be confused with science , and for me Audio is Engineering


[[ Ciao T ]]

Ci sentiamo...dopo

Jorge

 

Hi,

This becomes highly philosophical at this point.

Well, as we can safely state that electronic devices and system are always non-linear and subject to many forms of distortion which can only be traded off against each other (eg THD can be lowered at the expense of higher PIM) we can surmise from the start that "harmonic spectrum shaping" of distortion is much more relavant than any absolute amounts. In fact this has been a matter of record since at least the 1950's (Walker, Crowhurst, Bereskin, Kiebert et al.). More recently the point was renforced by Geddes/Lee.

Hmmm. So, if all distortion is objectionable, have you had your ears re-modeled yet? And what are you using to play music?

In any audio system they are demonstrably the highest contributor to distortion (around 30%+ THD for the ears mechanical system @ 92db/200Hz), followed by speakers.

My contention is simply, that if you set up correctly the passive I/V conversion for actually any given DAC the deterioration of linearity and/or increase in THD is notional and the particular type of non-linearity causes only moderate levels of very low order components, which are due to the way the human hearing works inaudible.

In order for 2nd Harmonics to become reliably audible they need to reach well above 1%, usually 3% 2nd harmonics are considered reliably audible. Correctly set up the TDA1543 offers much lower levels of distortion, so any arguments about this level of distorttion are purely academic and unrelated to the real world, where people use such a DAC to listen to music.

This contains a Philips TDA1540 which has a DC compiance on the output specified at +/-25mV, but realistic has a clipping voltage at a few 100mV, just like the TDA1541. Either of these requires the I/V resistor to be kept low, due to the internal contruction of the Chip. The same does not apply to the TDA1543 and to a lesser degree the TDA1545. It equally does not apply to the Burr Brown PCM56/61 and related series, but it does apply to the more recent Burr Brown DAC's stating with the PCM63 through to the PCM1704.

Sorry, that is plainly wrong, actually. Timing and fidelity will be just fine, if you make sure that your mechanical resonance system is critically damped, which is how it should be done for good linearity anyway, instead of using the voicecoil as eddy current brake. It is true that a driver designed for voltage drive is not suited to de driven by a current surce amplifier, but that is execution and not principle related.

If you measure a distinctive resonance, you have merely confirmed that you designed a poor speaker, in the absolute sense, nothing else. To damp mechanical resonances by sending current back into the amplifier is an extremely crude, inefficient and nonlinear approach to controlling resonance. It is of course one that requires no thought and is cheapest, which is why it is seen so often, but that does not make it any more of a good approach.

I am not sure what you read in my writing. However, it very easy to demonstrate that a speakers cone movement is porportional only and entierly to the current flowing in the voicecoil. It is equally very easy to demonstrate that if we apply a socalled voltage source (in other words an amplifier with zero output impedance) we will experience a distortion of the current in the voicecoil due to eddy current losses in the solid ferromagnetic polepieces, which unfortunatly are essential for the functioning of the moving coil system. In addition you experience also thermal compression which si significant (as much as 6db at full power) which BTW also alters the drivers T/S parameters or in other words the elecrtical damping if used.

Tell that to Prof. Dr. Hawkesford and Paul Mills. And please them in the JAES where they published their articles on the subject in the 80's. They demonstrate quite comprehensively what the reality is. If you disagree with them, please correct their error in said publication, if you can that is.

Then perhaps it would benefit you if you made sure you are aware of comparably recent (eg post 1930's) developments in the field of audio engineering. At the very least it saves egg on your face if someone chooses to expose your ignorance.

Ciao T

 

Cool - thanks - I mis-understood what you were saying

Subjectively, yes.

I received mine on a Monday. Out of the box it represented an improvement over the Squeezey's DAC but the Planet 2000 sounded better. I was in the middle of re-building my server (v.ill disc) at the time so could only run the Squeezy off the laptop. Got the server up and running mid to late in the week and therefore was able to leave it streaming 1 & 0's to the DAC all day and night.

After about 3 days of near constant running it was presenting the music more co-hesively and dynamically - fuller sound. Very roughly I'd say that by about 100 hours running time it was (pick whichever of the following suits your world view):
1) fully run in
2) close enough to fully run in to make any marginal improvements pass un-noticed
3) I was fully acoustomed to the presentation and run in is bollocks

So yeah - I'd expect that there is more to come from your unit if you only have a handfull of hours clocked up (fault rectification aside).

Regards,

Stuart.

 

Man, you are really lost... you must make up your mind...

Either you believe in fighting distortion (by means of trimming your DACs) or you don't... which will be?


PS: If our ears "distort" how is our perceived reality?! How can we localize and identify a sound source in the dark?!

All I hope is hearing, and only hearing my ears' distortion... not your equipment's distortion!

 

Does anyone know of a utility for calculating I/V and Vref resistor values for a TDA1543?

TIA

I'm using +5v, 910R I/V and 1K0 Vref, based on one of 3DS' old posts.

 

Chris, its really hard to say of its improved, I got mine just after xmas and Id say its been on everyday since so its had plenty of time. Im becoming more of a sceptic when it comes to burning-in periods, I'll gladly accept that components perform better once warmed up but anything more, Im still to be convinced. It makes more sense to me that in round terms, after the initial switch-on the only way is down, components have a finite life. Getting back to the subject, adding the psu made a big difference and it is really needed to get it to really sing.

 

T-bone - look up "electrolytic capacitor forming" on google. They can and do change, and I've measured variations in amplifiers due to it.

 

Hi,

My mind is quite clear as are my posts.

1) Clipping type distortion must be avoided.
2) Distortion below clipping is a complex subject and the right answer is not always "the lower the measured distortion the better".

I don't believe anything actually. I actively disbelieve. I prefer to know.

As said above, gross clipping must be avoided in all conditions (what Isaac measured looked well past 10% THD). Below that I believe in minimising the AUDIBILITY of distortion which is not the same as minimising the one-dimensional THD Number. If you don't believe, take the Geddes Test.

That is the point, you NEVER percieve reality. You percieve an interpreted and processed form of it.

And as noted, the distortion mechanisms in the ear have been long known. Here a quote from an article I wrote in the late 90's:

"Experiments by Patterson in 1969 revealed that if a PURE tone of 200Hz is presented to the ear with a SPL of 94db harmonics are produced within the ear at 400Hz, 600Hz, 800Hz, 1kHz, and 1.2 kHz with magnitudes of 84dB, 76dB, 70dB, 66dB and 60dB. This represents a roll-off of around 12dB per octave. The distortion levels are thus extremely high, corresponding to 32, 12.6, 6.3, 4 and two per cent respectively. So the Ear itself produces over 30% Harmonic Distortion at 94db. Yet we ourselves perceive this kind of tone as ABSOLUTELY PURE. Our Brain indeed will effectively "filter out" the Distortion and let us hear the pure tone.


For the Reproduction of Music, as long as the Harmonic Spectrum produced by the COMBINATION of Amplifier and Speaker is significantly lower, but of an IDENTICAL Spectrum, this harmonic distortion of the playback mechanism will be masked by the Ear/Brain system. Again, we will hear a pure tone despite a VERY HIGH level of distortion. It simply means that we cannot hear it. I am indeed saying that under CERTAIN conditions a MEASURED level of Harmonic Distortion amounting to about 10% is inaudible to the human ear. This should absolutely not be construed as claiming that 10% THD are always inaudible, but rather that at certain sound pressure levels and for certain spectral compositions for the Distortion 10% THD are inaudible.


This effect called masking does obviously also apply to the Intermodulation Distortion produced by the same non-linearity's leading to the harmonic Distortion. The BBC's D.E.L. Shorter wrote several articles on the subject in the 1950's and 1960's, which I'm still trying to locate, I have info only of one and then in the abstract rather than the whole article.


At the same time, if we had distortion that does not have the specific and monotonic structure of distortion present in the ear, the resulting harmonic spectrum and intermodulation distortion will NOT be fully masked by the Ear/Brain system and the tone will be perceived as impure. With many Instruments playing together, the intermodulation distortion actually becomes dominant over the harmonic distortion. Indeed, once more than twelve independent sinewaves are present intermodulation distortion will dominate.


If we then have a lot of odd order or high order harmonic distortion, we get a lot of Intermodulation side-bands spaced very close to the original tone. Such sidebands are much more audible than the widely spaced sidebands created by low order and even order harmonics. Subjectively the tone will sound not so much distorted, but "dirty". A different impurity, so to speak. Try massed strings to listen for intermodulation distortion and single pure instruments (again strings or something like an acoustic guitar or piano) to listen for harmonic distortion."

(from "Some thoughts about singleended Valve Amplifiers - An introduction by Thorsten Loesch")

That is a very good question. Localisation has a lot to do with the transients (you will find it difficult to locate the source of a steady state noise but very easy to pinpoint the crack of a breaking branch or twig or the click when someone unlatches the safety on a rifle). Distortion in the traditional sense is something that affects the waveshape, which has more to do with the percieved tonaity.

That is exactly what I try to achieve. And the solution is not neccesarily to make a device with arbitrarily low (but non zero) measured THD from a given non-linear device, but sometimes to accept HIGHER level of distortion if they follow a pattern that LESS AUDIBLE than the lower measured THD pattern.

Ciao T

 

Hi,

I guess I could write a spreadsheet, but as there is so much variation between chips (> +/-15% variation of Ifs and +/-5% for Vref) you pretty much have to tune then to match every individual IC or simply assume "worst case" conditions. If you assume worst case conditions and design for that you will loose a lot of available dynamic range and you might as well build and active I/V stage.

Ciao T

 

I'll just take your word for it, Im too tired and my head hurts.

 

Have you measured the pain in your head, or is this merely a subjective opinion?

 

stuart / t-bone.

thanks for the replies, the thoughts at LordSummits bake of were that i needed to leave the box on for a good few days with 1 and 0's passing through which i'll do just as soon as the little beast returns.

Given that pre fault comments were favouable it can only get better

A dedicated PSU was also discussed and certainly appears to be the other way forward. Be interesting to see first feedback on dereks PSU as well. Derek has all but said i cant order one until i have the dac back and am happy with it, good customer service, though not without its frustrations!

Will keep you informed

edited to add - stuart - your 3 point options were great - i now understand that certain components have running in requirement, i also believe that we also need running in to any changes in our systems.

 

That's both arrogant and presumptious. You've never even heard a NOS DAC! You might well be able to tell the difference between the two but there's no way you'd be able to hear the "distortion" in the NOS DAC.

I'd like to see a 15kHz sinewave output from a NOS DAC that is known to not be faulty but anyway, being able to see distortion on the scope and being able to hear it are two quite different things. The Stereophile trace showed the NOS DAC representing a 20kHz sinewave as a square wave. There is no way that you, or any other human being, can tell apart a 20kHz sinewave from a 20kHz square wave by ear. The distortion in this case is made up of frequency fundamentals well beyond the limits of human hearing.

Michael.

 

Now, guys,

I might be close to that area tomorrow and could give you a help.
On the behalf of the other members who won't be able to attend your match, I can act as a referee and testify in favor of whoever bribes me most.

(BerylliumDust, I once told you that player only performs well using the balanced outputs. AFAIK, you have only tried the single-ended ones.)

Regards,

106

 

Now, that is philosophical... I believe that knowledge = cience.

This is in profound contradiction to what you say next...

"you will find it difficult to locate the source of a steady state noise but very easy to pinpoint the crack of a breaking branch or twig or the click when someone unlatches the safety on a rifle)."

... and you should know that pure tones are rarely heard in nature.

This is something you believe in, or that you know?

Because everything that affects the waveshape is distortion, and the ear is many times more sensible to transients (like you say above) than to the perceived tonality or THD.

 

Michael,

You misunderstood me... I'm not saying that your system is f**ked up, I'm just saying that if you could hear the difference between your present NOS DAC and your DAC64 to the point of wanting to sell it, I will also be able to hear it...

If there wasn't a NOS sound, an intrinsic distortion, what would be the point of buying one?