Joshua, the FFT was what I was using last night to 'optimize' my RIAA curve in my latest phono preamp design.
The FFT goes back to the 1960's and was discussed in IEEE articles then, to a great degree. It was a faster version of the Discrete Fourier Transform.
However, until we had decent and cheap A-D converters and reasonably fast microprocessors, it was a special and expensive piece of test equipment that could do a FFT with its attendant
advantages. In 1974, we paid $50,000 for a Tektronix PDP-11 based FFT analyzer, for our lab in Switzerland. We even had to go to school to run the machine at Tektronix in Oregon.
Later, test equipment began to be made for the military industrial complex such as the HP3562 that was only the size of a very large suitcase and cost only $25,000, that used FFT for its analysis. This replaced the HP3580 Spectrum Analyzer for all practical purposes, that was based on conventional test equipment approaches, much as computer circuit simulation has replaced the Analog Computer, of previous years.
Today, almost everybody has some form of FFT based analyzer on their PC's, but I didn't have anything useful until about 10 years ago. It can be handy, but not absolutely necessary, except for acoustical measurement where it is very helpful in removing the room reflections.
The FFT goes back to the 1960's and was discussed in IEEE articles then, to a great degree. It was a faster version of the Discrete Fourier Transform.
However, until we had decent and cheap A-D converters and reasonably fast microprocessors, it was a special and expensive piece of test equipment that could do a FFT with its attendant
advantages. In 1974, we paid $50,000 for a Tektronix PDP-11 based FFT analyzer, for our lab in Switzerland. We even had to go to school to run the machine at Tektronix in Oregon.
Later, test equipment began to be made for the military industrial complex such as the HP3562 that was only the size of a very large suitcase and cost only $25,000, that used FFT for its analysis. This replaced the HP3580 Spectrum Analyzer for all practical purposes, that was based on conventional test equipment approaches, much as computer circuit simulation has replaced the Analog Computer, of previous years.
Today, almost everybody has some form of FFT based analyzer on their PC's, but I didn't have anything useful until about 10 years ago. It can be handy, but not absolutely necessary, except for acoustical measurement where it is very helpful in removing the room reflections.
john curl said:
It can be VERY handy. FFT-based multitones with, say 31 simultaneous tones (there is an ISO standard), will let you measure freq response, THD, IMD, noise etc in one test. The 31-tone signal looks very much like music, so you can actually measure your equipment in circumstances very close to actual use. It's like measuring non-linear artifacts and noise in the presence of music. Awesome.
Jan Didden
There are practical limitations to FFT processing, and analog can be just as good, in many cases.
However, it would be best, Joshua, if you just 'Googled' your question first, and saved us from providing you definitions of processes, etc. It would be most likely more complete, and saves time.
However, it would be best, Joshua, if you just 'Googled' your question first, and saved us from providing you definitions of processes, etc. It would be most likely more complete, and saves time.
Jan, an HP3580 can resolve that. It just takes a longer time to do. We did much the same thing in 1976 in our TIM research.
Yes but how would you GENERATE that waveform, with enough spectral purity to allow measurements down to -120dB or better?
And your HP3580 has, what, 80dB dynamic range? Forget it!
Edit:
HP 3580 A is a Low Frequency High Performance Spectrum Analyzer.
Its 1 Hz Bandwidth allows the user to examine noise and extraneous signal content close in to a signal of interest.
- Frequency range: 5 Hz to 50 kHz
- Bandwidths: 1/3/10/30/100/300 Hz
Digital storage of two traces. Both may be simultaneously displayed for easy comparison.
Amplitude character
- Instrument range: linear 20 V to 100 nV full scale; logar.: +30 to -150 dBm
- Dynamic range: 80 dB
Sweep characteristics
- Scan width: 50 Hz to 50 kHz
- Log sweep: 20 Hz to 43 kHz
- Sweep time: 0,1 s to 2000 s
Built-in Tracking Generator
Analog recorder output.
Mechanical frequency display.
BTW How do you use FFT to optimize your RIAA curve?
Jan Didden
And your HP3580 has, what, 80dB dynamic range? Forget it!
Edit:
HP 3580 A is a Low Frequency High Performance Spectrum Analyzer.
Its 1 Hz Bandwidth allows the user to examine noise and extraneous signal content close in to a signal of interest.
- Frequency range: 5 Hz to 50 kHz
- Bandwidths: 1/3/10/30/100/300 Hz
Digital storage of two traces. Both may be simultaneously displayed for easy comparison.
Amplitude character
- Instrument range: linear 20 V to 100 nV full scale; logar.: +30 to -150 dBm
- Dynamic range: 80 dB
Sweep characteristics
- Scan width: 50 Hz to 50 kHz
- Log sweep: 20 Hz to 43 kHz
- Sweep time: 0,1 s to 2000 s
Built-in Tracking Generator
Analog recorder output.
Mechanical frequency display.
BTW How do you use FFT to optimize your RIAA curve?
Jan Didden
PMA said:
Wow!
PMA said:
What do you think? And why is that of interest?
http://www.helmut-singer.de/pdf/hp3580a.pdf
Jan Didden
GRollins said:
Gee, one lousy nights sleep and I'm over 50 responses behind.
Gray,
It's obvious you are a writer and comfortable on the keyboard.
I already know how to design equipment (both audio and non audio) with feedback. I design my audio equipment without feedback. I find it more of a challenge and more rewarding for me. I also prefer the way it sounds without feedback. That is, of course, an opinion on my part and not scientifically tested and verified.
I simply wondered what you felt was an achievable goal without feedback. Your response tells me you either do not know a great deal about audio design or you simply do not care if your work measures poorly. Your distortion and bandwidth numbers are ludricrous by standards achieved (I really hate to say this) 25 to 30 years ago.
I would like to see some of your work. Can you post a link?
anatech said:
I have a saying: "Fish don't notice water."
You have written a lengthy post attempting to justify your point of view and nearly every paragraph is just another way of expressing either your prejudice or your displeasure at being called out on it. You don't notice your prejudice because you live in it, relate most to people who share it, and have it so deeply ingrained in your world view that you can't imagine any other perspective to have any merit at all.
...Just like the fish who doesn't notice the water around him. All his friends swim, breathe, and see everything through the same water. Naturally the world looks the same to them. Things look a little different from the perspective of someone who lives in air, though.
Trying to respond to your post line by line would take hours; it would be like deconstructing a Creationist book's attempt to defend the young Earth concept. I just can't justify the time today.
I'll try to hit some highlights so as to demonstrate that I'm not just trying to cop out when faced with some sort of overwhelming logic in your part:
--Top line--BINGO! After denying that you are at risk of prejudice due to measurements before listening, you admit that you make measurements before listening. I don't think I could pay someone to say it any more clearly.
--Next--Your use of the words 'no evidence' actually translates as 'no evidence that you will accept.' That's not at all the same thing. If I were to attempt to describe a color that I see as I'm looking out the window here in SC, it wouldn't be surprising if we had a breakdown in communication. We'd get as far as blue or yellow, but giving you the exact shade of blue or yellow would be difficult. And no, something like a color chip as a reference isn't always the answer. Case in point--I and my wife were driving in the mountains in NC. We rounded a curve and both gasped. We were looking at a blue horse. WTF? The horse was in the shade, lit by north light (hence bluer), and was possessed of a sort of pale gray coat that supported an impression of blue more readily than, say, a brown coat would have. We pulled over to the side of the road to observe, only to have the horse move from where he was standing, which ruined the effect. Could I describe the color of that horse to you? No. And even had I matched its coat to a color chip, you would be skeptical, perhaps even with my explanation of the circumstances. With audio, we are limited by the fact that we are at distance. Just as the 'blue' horse was a you had to be there sort of thing.
--Which segues into a line that beautifully demonstrates my 'fish don't notice water' aphorism. You think you're right and as a standard, you compare yourself to other fish...but only other fish. Any other perspective need not apply. So you have--like Fundamentalists--a self-reinforcing belief system which boils down to "everybody believes what I believe." Well, yeah, they do. As long as you remain within your chosen group of fellow believers and reject any other viewpoint.
--Yes, people who have test instruments do have more experience...with test instruments.
I've never claimed that any effect was somehow supernatural, in the literal meaning of 'outside of physical law.' I approach our current knowledge of physics, chemistry, etc. with a little more humility than you do, however. We don't know everything yet. Your statements at this point smack of revisionist history (which you later protest) in that you ignore the fact that the very reason people now have proof that you would call substantive is because so-called golden ears heard it first, which lead to measurements. People who believe as you do are faced with an unpleasant conundrum. What on earth do you do when something new is proved? All your words about how it was impossible prior to the day it was proved are revealed to be nothing more than smoke on the wind. Do you sweep it under the rug and pretend you never said those things? Do you acknowledge that the effect in question exists and that you were wrong? Do you attempt to claim that you knew it all along, even if your prior words prove you to be a liar? What do you do? Not everything proposed as a valid audio tweak/whatever makes it, but a fair number do, given enough time. Sorry it takes a while, but that's life for you.
--I'm skipping a fair swath of stuff that either makes no sense whatsoever (old test equipment? huh? where did I mention old test equipment?) or I've already responded.
--I just had to leave in the next lines...they're just too perfect. Once more, I could not pay to have someone more clearly expose their prejudices than to say, "don't expect too much intelligence..." and, "hearing things that aren't there." Perfect! You not only insult the intelligence of people who listen, but you follow it up with a blanket denial that there is anything more to be discovered. Tell me...which option will you choose from those listed above when the next item is proved? Doug Self, to his credit, chose to admit he was wrong to have blasted people who insisted that absolute polarity was audible, once it was proven. But he is in a distinct minority.
--And finally, to wrap this up, you went from claiming that measurements-oriented folks accept uncertainty in a previous post to a crystal-clear statement that they were always right. Hmmm... There are any number of ways I could respond to this, but the most efficient time-wise is to simply refer you to the absolute polarity question. People claimed it was audible for years, only to be shouted down by those who refused to face a simple observational fact that many of them could have demonstrated for themselves in minutes and at no cost. What have they had to change their minds on? Well, golly, here's a good example. To claim otherwise is revisionist history. Why do you think someone even undertook the test if not because others said there was something there to test for? Listeners first, then along came the confirming tests.
Uncertainty? What uncertainty, Chris? Show me the 'uncertainty' in your post wherein you admit that maybe, just maybe, the measurements might not cover everything. It's not there. Period.
Might I suggest that you go back and read a post of mine wherein I suggested a more humble approach? "I have not tried XX." "I tried XX and did/did not hear a difference." Full stop. That's honest observational science.
--Incidentally, I've got two degrees, one in psychology. I happen to know a fair amount about testing and statistical methods. Your implied insults about my not considering the possibility of suggestibility, prejudicial mindsets, and so forth don't impress me in the least. Refer back to my last dozen posts or so, should you doubt that I've acknowledged same in print. Where's your admission that you suffer from the same, human tendencies?
My other degree is in geology, which involves quite a bit of chemistry and physics. Indeed, I had intended to triple major and take a degree in physics, which I've always enjoyed, but policy was double major being the limit. Bummer. I also took quite a few courses in electronics--which would have stood me in good stead had I been allowed to take physics--but I took them because I had already been interested in electronics for quite some time.
In short, you have mistaken the depth of your conviction for the force of your logic. Just like a Fundamentalist.
Grey
Steve Dunlap said:
In the context of your wording, I simply don't care if it 'measures poorly.' Measures poorly according to whose standards? Your post seems to indicate that you feel THD to be valid below .1%. I don't. I'm not in some sort of a race to see if I can achieve the lowest distortion ever. If that's your goal, then by all means pursue it. From where I sit, you oil the squeakiest wheel first. Once THD gets below some nominal value, I don't care to pursue it. I used to sell audio gear back during the era when .0001% range numbers were common, so I'm well aware that lower numbers are achievable. And so I should attempt to recreate those figures...? Nah. Not interested. If I get that, great. If I don't, great. You can, though, if you think it's that important.
The GR-25 can be found here:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=120673
Grey
john curl said:Good reply, Grey. I would rather you, than me, reply in detail at this time. I'm tired!
Jeez, guys, quit posting while I'm responding to the previous one...
John,
Hate to say it, fella, but I'm going to have to let you carry the load for a while. I've used up entirely too much time on this over the last week or so (I'm not a particularly fast typist...ironic, perhaps, but there it is) and I've got to get back to other things, like the boys and blocking out our '08 taxes before turning them over to the accountant, etc.
Besides, I have limited patience for some of these people whose prejudices are so prominently on display. 'Round these parts we've still got this legacy of hatred left over from the slavery days. The "I'm not prejudiced, I just don't like black people" line can be heard even today. And, no, they don't seem to be aware that they just gave themselves away. From their point of view, that's somehow a valid, non-contradictory statement. A couple of these recent posts are trending a little too far in that direction and I don't see that there's much to be gained by wasting even more time arguing with someone whose mind is that far removed from reality. Once you get to revisionist history, there's no point in going further.
Grey
Hi Grey,
What I attempted to do was to answer your points as cleanly as possible. Some of those were the same thing asked a different way, much the same way a psychologist may interview someone. I did well in my psychology courses, but I majored in electronics. Hey, that's what we are discussing - electronics! That and the ways we measure performance.
I am not the one who is defending myself here (nice try though). I am one of those people who accept the importance of listening to a design, but I also understand the importance of what measurements can tell me also. I consider data from each overall method, and I know I'm on the right track with a design when they both agree.
Now, Grey, you are the one who is ignoring the useful information that some measurements can give you. You are the one who doesn't look for agreement between measurements and listening tests. In fact, you are the one who advocates ignoring any information that comes from measurements. It is as if you are in a religious cult, "I can't prove it, but you must believe me! Don't look at measurements, for they are the numbers of the devil!". The impassioned plea of someone who doesn't really understand how to interpret this extra information.
Could it be that some of those who can not afford some good test equipment counter that short coming by determining that they do not require this knowledge to better execute an analog design? The have-nots railing against those who have the resources? I suspect there is some truth to that hypothesis. You, as a student of human nature, have to accept this as a possibility for some people, if not yourself.
Let me tell you something Grey. For years and years I desperately wanted better test equipment. I knew that there was information that would really help me with designs if I could only get access to the equipment I needed. For years I did what I could with the tools I had. I even investigated methods for getting more information out of the gear I had. So here I am, accepting that I didn't have enough information to become a better technician / designer, and admitting it. I had gone into debit to buy equipment to do my job better, some new, some used. Some time ago I was involved in an accident that left me unable to work. In fact, this accident also affected my memory and ability to think creatively as well. My prototypes and notes appear to be written and built by someone else. Out of desperation and fear, I did go deeply into debt in order to buy parts and more test equipment in order to relearn the things that I lost as a result of this accident. I have an idea of what I need to do to arrive at a spot that was equivalent to where I was before. The accompanying depression was / is severe, and you as a student of psychology should have some inkling of what this can do to someone. I lost "me". If you want, PM me and I'll give you a list of drugs I'm on now. I'm on as light a dose as we can use, but I'm still on 80 mg of Oxycontin / day + more other stuff. So as a result of depression and fear, I did buy more test equipment. Included is an HP 3585A, 3580A (early), 3336B, 3586B, 3324A and 339A, and more. At least I feel I am in a position to relearn now. My "replacement income" isn't nearly enough to support my wife, kids and I either. So for whatever reason, I have put my money where my mouth is. This is because the instruments are necessary.
Anyway, you are the one excluding information. Myself and others are accepting all of it. Measurements and listening both. You are one the defensive here, not me. Why can't just simply accept that some measurements are a necessary part of the package? This is my question to you and John.
-Chris
Nope, but that's your take on things I guess. I have noticed that most of your posts relating to people's views can just as easily be applied to you, the reverse.
What I attempted to do was to answer your points as cleanly as possible. Some of those were the same thing asked a different way, much the same way a psychologist may interview someone. I did well in my psychology courses, but I majored in electronics. Hey, that's what we are discussing - electronics! That and the ways we measure performance.
I find this extremely amusing! Thank you Grey, because it speaks to a point I made earlier.
I am not the one who is defending myself here (nice try though). I am one of those people who accept the importance of listening to a design, but I also understand the importance of what measurements can tell me also. I consider data from each overall method, and I know I'm on the right track with a design when they both agree.
Now, Grey, you are the one who is ignoring the useful information that some measurements can give you. You are the one who doesn't look for agreement between measurements and listening tests. In fact, you are the one who advocates ignoring any information that comes from measurements. It is as if you are in a religious cult, "I can't prove it, but you must believe me! Don't look at measurements, for they are the numbers of the devil!". The impassioned plea of someone who doesn't really understand how to interpret this extra information.
Could it be that some of those who can not afford some good test equipment counter that short coming by determining that they do not require this knowledge to better execute an analog design? The have-nots railing against those who have the resources? I suspect there is some truth to that hypothesis. You, as a student of human nature, have to accept this as a possibility for some people, if not yourself.
Let me tell you something Grey. For years and years I desperately wanted better test equipment. I knew that there was information that would really help me with designs if I could only get access to the equipment I needed. For years I did what I could with the tools I had. I even investigated methods for getting more information out of the gear I had. So here I am, accepting that I didn't have enough information to become a better technician / designer, and admitting it. I had gone into debit to buy equipment to do my job better, some new, some used. Some time ago I was involved in an accident that left me unable to work. In fact, this accident also affected my memory and ability to think creatively as well. My prototypes and notes appear to be written and built by someone else. Out of desperation and fear, I did go deeply into debt in order to buy parts and more test equipment in order to relearn the things that I lost as a result of this accident. I have an idea of what I need to do to arrive at a spot that was equivalent to where I was before. The accompanying depression was / is severe, and you as a student of psychology should have some inkling of what this can do to someone. I lost "me". If you want, PM me and I'll give you a list of drugs I'm on now. I'm on as light a dose as we can use, but I'm still on 80 mg of Oxycontin / day + more other stuff. So as a result of depression and fear, I did buy more test equipment. Included is an HP 3585A, 3580A (early), 3336B, 3586B, 3324A and 339A, and more. At least I feel I am in a position to relearn now. My "replacement income" isn't nearly enough to support my wife, kids and I either. So for whatever reason, I have put my money where my mouth is. This is because the instruments are necessary.
Anyway, you are the one excluding information. Myself and others are accepting all of it. Measurements and listening both. You are one the defensive here, not me. Why can't just simply accept that some measurements are a necessary part of the package? This is my question to you and John.
-Chris
Any extreme position is wrong, regardless it is measurement assement only or listening assesment only.
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