What is PRAT?

[dantheman]

I think we all know what it is when we hear it and it's probably part of what first drew me to analog, but what's behind it? Here's an article that may provide an explanation or at least part of it:
http://www.physics.sc.edu/kunchur/paper ... Foster.pdf
Do we now have more evidence for super resolution not only in the frequency domain, but in time as well?

What's your thoughts?

Anyone else have a good explanation/example of research?

thanks,

Dan

[hurdy_gurdyman]

Interesting article. It happens to agree with some of my own thoughts on this, and gave me a couple of new things to chew on.

As for PRaT, I know it when I hear it, but don't expect me to describe or explain it. It does have a lot to do with why I prefer analog to digital, idler drive turntables over belt drive, and maybe even has something to do with my love of tubes over solid state. OB speakers seem to naturally have more PRat than box speakers (so do horns).

Dave

[dantheman]

Careful Dave. It sounds like we may agree again. This article may also hint at advantages of FRers or coax drivers as well.

[Bob from Florida]

Interesting article to be sure. Not very many have access to his selection of test equipment. Time domain accuracy is certainly important and the less you do to introduce errors the better. I believe this is the primary reason that simple gear - less electronics - usually sounds better than more complicated gear. I work on Magnetic Resonce Imagers - installation and repair of MRI's - for a living. TIme domain changes in the system as a whole will make the final image appear "smeared" instead of sharp and in focus. Specifically, the calibrated variations in the magnetic field produced by the Gradient Coils in a MRI can be thrown off by cables being the wrong length. There is a calibration for this - a variable delay that will bring things back into focus - but this is not an item one is likely to have in ones stereo system.....

Bob

[hurdy_gurdyman]

Careful Dave. It sounds like we may agree again. This article may also hint at advantages of FRers or coax drivers as well.

No argument from me on that.

Another system besides Coax or fullrange that should work good is using a fullrange, or very wide range, driver with bass augmenter and super tweeter added. I've played with this concept with my old EV LS-12's and LS-8's. Makes a very coherent sound with the tweeters crossed high (8-10 kHz or so) and the Augmenters below 100 Hz (maybe 200 Hz with the 8 incher). The wizzer cones make decent dispersion higher up. I plan on revisiting this idea someday with a few ideas I've been thinking on. One thing I'm not revisiting is conventional three way box speakers with drivers all crossed at the lowest end of their range, thus putting a crossover in the 1000 Hz area, more or less. This almost always seems to have a bad effect on PRaT. Our ears are extremely sensitive here, and any potential phase issues can be detected, either consciously or sub-consciously.

Dave

[dantheman]

Hmm, I decided I had better just pull this post.

Thanks guys,

Dan

[Rock4016]

Along the lines that Dave said, I think that's why the BassZilla has a strong following. Using an extended range driver as a mid that is crossed over high and low can sound fantastic.

[dantheman]

So many aspects of sound reproduction.............. Seems no matter which you pick to perfect, it adversely effects another. Probably best to learn as much as we can about human perception in order to perfect playback to cater to perception's strengths and weaknesses. The other end of the conundrum is the recording. Not much we can do about what is done there except buy what's well done. Problem is, the majority of audio media purchasers could care less. Audiophiles are fighting a losing battle in this respect. What to do, what to do? Dave probably has the most insight into recording. Is there a site where you can just post your own recordings w/o having to do anything else? Like a flickr for audio?

Thanks,

Dan

[TerryG]

True there is always compromises, but I feel balance is where we all wish to be whether we realise it or not. The thing is you can't ignore something for something else, it is not a matter of choosing to perfect one thing over another. For me I go for the most difficult to obtain knowing the other aspects will be easy to obtain once I have the more difficult aspects. The problem is that the industry doesn't want us to understand the details of audio, they just want us to understand it is complex so they can tell us what will make things sound good. How often do you see a manufacture focus on one special thing about their product while not telling the truth about the other aspects, in order to sell what they make. It can all be very frustrating, or at least it use to be before the internet, now I have more knowledge at my finger tips. The problem now is the perpetuated myths out there still in audio, these are my pet peeves that I consider it my mission to dispel them when possible. I really stuggle on how to do this in a dignified manner, but I think I have done fairly well the last few years.

T

[dantheman]

Hey T, excellent post! I agree with most of what you said, which is nice for a change. What do you think are the most difficult aspects of balanced (I'd prefer to read "accurate, spacious and thus thoroughly enjoyable" here, but I think that's just semantics) sound reproduction? To me, if those most difficult aspects of reproduction have been shown to be less important by science, then why bother trying to optimize them first? (I'm not guessing what you are referring to, just stating my philosophy and its rationale) As far as I'm concerned, all aspects of accurate reproduction seem about even in difficulty--ain't none of them easy if all are absolutely adhered to. So we have to pick our priorities wisely. Well I guess that is unless you feel having a FRer, any old amp and cd player is the ultimate in reproduction. That's fairly easy, but wrong all at the same time with all the present drivers available (if you believe science and you're human). So I think picking the right things to place the most emphasis on is extremely important. IMO we're best off to use what science has shown to be true first. Then we can guess about what else through experimentation. Getting what science suggests is difficult, but it has been demonstrated in a meaningful way to work. It taught me why I loved my previous OB design when in test baffles, then gradually thought less of them after building the final baffle(which was different and optimized for a flat on axis response). Few designers are even close or looking in the direction of science, though all abide by its laws. In any case, Kunchur's work suggests something. The usefulness in sound reproduction has not been demonstrated in a meaningful way yet though it doesn't mean it's useless. Hopefully more work will be done.

Dan

[TerryG]

Dan,

Often times it seems to me your thinking to specific rather than over all, that is why I brought up the word "balance" because often times one factor effects the others. Well not just often times, lets say most if not all of the time.

The aspect I feel most important is dynamics, and this one factor is related to other factors so closely you can't ignore it. This in my opinion is the key to many things, as dynamics will effect frequency response, and distortion will effect frequency response as well. So it is possible to "fix" frequency response, but still have other things way out of wack that it is like cutting off your nose inspite of your face. So often we measure frequency response with just one amplitude that we are not getting the full picture of it, and often times we measure frequency response at what WE consider the worse case senerio that we ignore other factors. I was on the testing specification band wagon of the 1980's at the very begining, but later I found I was barking up the wrong tree. Too look at a tube amp and consider it better based on tests would seem foolish as SS amps seem to be far superior, but they do some things right inspite of their failure. Some have even asked me why I like to listen to distortion, because tube amps they say have so much more distortion, and that is true if you look purely at the specifications. But I worked in a lab where we put a 2 watt tube amp (My then Decware amp) against a 30 watt SS amp (Technics receiver, with very low published specifications) in a real world set up with speakers, and the tube amp had less distortion by a factor of 10 at least. I didn't really need a distortion meter to know that the tube amp sounded better, and that I liked it better, and that there was a measurable reason as to why I liked it better. Simply put if it sounds good it is good, our hears are a far more sensitive instruments that what was previously thought, as now they are realizing the redbook standard isn't measuring up with regard to what is audible. The difference between one amplifier and another can rest in less than 1% of a difference of distortion and our ears hear that and other things.

Measurements are helpful and they have definitely influenced my pursuits as to what I like to listen to, and how to get there, but I frankly don't trust most sources of measurements myself included really. They are too much like statistics, the interpretation of them is a weighty factor. I would rather trust my ears, they have proven to be much more truthful.

Take for example the two amplifiers I mentioned previously that I had the opportunity to prove to an electronics engineer that you can't just read spec's and go from there. At 1K Hz with a resistive load the SS amp appeared by the manufactures standards to be the better amplifier with less distortion, with as a result better frequency response. But the SS amp was a class AB amplifier, and there is crossover distortion no matter how much you tried to adjust for it with an inductive load, as a result the SS amp at 20K Hz measured far worse under all conditions. It was literally choking at 20K Hz. The reason being is that its frequency extension was not far above 20K Hz, and distortion in electronic devices increase logrithmicaly on a curve, so not just how much distortion an amplifier have is important at 1K Hz, but what is its upper limit with regard to frequency is also important. Because that curve could be gradual if it has a frequency extension is up to 100K Hz rather than 25K Hz, if an amp had a upper frequency limit of 25K Hz its maximum distortion would be there, not leaving much room for a good figure at 20K Hz. Now if you take that as a fact there are all sort of implications this makes and difficulties it presents for an amplifiers performance. Not to mention that this figures are with resistive loads, when you put a inductive load into the picture the real colors of these amplifiers became apparent and you could not ignore one things in favor of another, you can to consider the entire picture. But I learned in a very short period of time that if you concentrate on dynamics, something you can tangibly hear, and discribe, that you can also fix other factors that make it possible thereby also helping other factors like distortions, frequency response, phase problems, and there many reasons why. So scientists may say that dynamics should be the least of our worries because we don't perceive them as much as other factors, but if you concentrate on dynamics others things naturally follow and it sure is a whole lot less brain damage. And I don't need a lot of test equipment to work on them, although I must admitt it would make things a lot easier. If you just pay attention to some basic principles then other factors like wild frequency plots won't get out of hand, but I find them really not all that common. There is a reason I gave up on single driver speakers, they just can't do what I want. I don't argue that they can sound good, they just aren't for me, if people are happy with them then more power to those people.

Thats enough for now.

T

T

[dantheman]

Hey T, sometimes I think we are on the same page, other times, well less so. My guess is that you want to read into what I say instead of just read what I say. It seems to be where we don't get each other. So far this thread is going well though. I agree with your last post as well, but I have one thing that I just don't get: Why is the FR of an amplifier important to you?

Dan

[TerryG]

Dan,

My response was carefully calculated according to previous agendas, we disagree on some points, that is fine we can agree to disagree. I was trying to give a little background so that my thoughts just were not without cause to some. It seems the longer your at this game of audio you tend to learn where the short cuts are.

As far as frequency response of a amplifier it is not that the FR is of an overriding importance but that you can tell a lot about an amplifier by this. All aspects of an amplifier I like to view like a mobile, each of them effects the other and so you can start with what is easiest to work with because of limited resources. Still I feel anyones best measuring tool is their own ears and you can tell a lot by them especially when they have been trained. Just last night my wife noticed the difference of how my CDP sounded compared to an LP of the same music.

T

[dantheman]

Actually, your last post sort of alludes to what I'm interested in now and why I started this thread. What faults become more problematic with what sources. Are timing errors in speakers more of an issue with analog gear than run of the mill digital (redbook or more compressed)? It seems many who do analog often prefer low order networks. Makes one wonder why there aren't any studies on it yet. At least none that I've seen. Another study I'd like to see would be the audibility type AB and B crossover distortion at low and high volumes. Anyone know if these exist?

BTW T, I do focus in on certain problems--the ones that have been demonstrated to be easily audible. I try not to weight things as equal if they've been shown otherwise. Perception of the recorded media is the key to me. The current recording/playback system isn't going to change, so we've got to optimize it. I ideally want to compile a list of most to least audible issues in audio, but that surely will never happen as it's a tall order. Then fix my system from top to bottom. Right now I'd say polar response and dynamics top my list, but below that............. a mystery to some degree. This is one of those mysteries.

Thanks,

Dan

[TerryG]

Your present recorded media doesn't have to change there are things you can do to get more out of whatever you have without too much cost. Believe it or not a tube stage can do a lot for digital, and a simple circuit can be tried for a phono pre.

I think I posted on the analog forum or perhaps it was above somewhere my perceptions with digital and vinyl. Oddly enough I don't feel it is do to the strickly digital or vinyl media as much as it is the old and new way of engineering each media's recordings. That is my belief anyway. I was just reading a study done where they thought when they first produced the redbook standard, that 11uS would not be audiable and it turned out it was, so now they are trying to change to a new standard as a result. Personally I feel the redbook standard can sound very good, but most players fall down in their quality, and the CD's themselves are mixed for ipods and other portable devices not home listening where dynamics are worth their effort.

T