Sound Quality Vs. Measurements

[nigel pearson]

Originally Posted by tvrgeek

If I close my eyes, can I believe? Of course it depends on the music. A lot of live music I would never tolerate in my house. I have walked out of too many concerts as the sound was so bad. My dream is someday, I will hear a recording of a single classical guitar that sounds like someone sitting ten feet from me. Maybe, but I am not as young as I was and the emphasis is now on portability not quality. I may never reach my dream but it is something to strive for. Instead, I head down to the coffee shop where Bruce pays when I can.

Try that at a classical concert . It is a very odd experience . Then do it at home . Equally odd . Put a picture with the sounds and suddenly OK sound becomes good sound ( my TV ) .

I was told that blindfolded people hear the orchestra in stereo . Even if musicians move around the first violin etc is always where it should be . They get the surprise of their lives to see the orchestra rearranged . Real life is mostly mono with lots of echo and depth . I like stereo and think it does no harm to classical if the hole in the middle is avoided . Make it sound good in genuine mono is one way . Not mono made from stereo ( BBC might be OK as they are fussy or were about mono that can be stereo , they perceived their No 1 audience as mono ) . Stereo for rock music is the music . As Gilbert Briggs ( Wharfedale speakers ) said we have two ears and be it mono or stereo two is best .

If you have some spare speakers of good phase similarity to your main pair try the Hafler idea . That is to retrieve out of phase information and send it to the back channels ( no decoder as such ) . I would guess some open air full range units ideal , maybe no box required ? The better car units are cheap and good . See if you find what I did . It is less fatiguing . Also Vinyl noise seems easier to live with . Now retry the test using Dolby devices ( home cinema , surround from stereo ) . You might like me find the magic has gone and the vinyl now miserable ( do not process the front so as to give it a chance ) ! The old KEF speakers were good with this as they embraced Quadrophonic and thought they would optimize the speakers for that . A friend " had " many LS3/5A , wish I had thought to do the test .

[a.wayne]

Originally Posted by Wavebourn

Symmetrical in each channel, and equal in both.

A few questions wave ,

1. so you are saying the slew rate is not as important as its symmetry ..
2. Does it matter if you have tilting on the low end
3 . Could you post a 40k wave of your amp ..

Regards ,

[dvv]

Originally Posted by a.wayne

A few questions wave ,

1. so you are saying the slew rate is not as important as its symmetry ..
2. Does it matter if you have tilting on the low end
3 . Could you post a 40k wave of your amp ..

Regards ,

I am not Wave, but your No.1 question hits a fat nerve with me, it's something I've dealt with for decades - literally.

A long, long time ago, in a galaxy far, far away, like many others, I had my period of being seduced by slew rates. Admittedly, at the time, the available choice of higher quality op amps was untinkably more limited than it is today, when it is almost unlimited. For audio, OP 27/37 were actually upmarket chips, while the general population had to make do with LF356 and its uncompensated brother LF357 (I liked them then and I still like them), and of course the TLO 81/82/84 family. They all worked as advertised, but it was hard to get really serious quality sound from them, even if some did, and even if they gave rise to ultra high end manufacturers, such as Germany's Burmester.

Then, some new kids from AD arrived, and the game changed. They were faster to much faster, and they sounded a whole lot better than their predecessors. BB 627 at al. also arrived, at BB prices, but they never managed to raise my blood pressure, presitigious names and all.

Like many others, my first thought was that it was the slew rate at work there, but then I noticed that AD op amps sounded better than other op amps with similar specifications. This begged the question what was AD doing that made them different from the others?

To cut a long story short, in the end, I realized that AD did have one thing VERY different from all others at one point. Everybody was hell bent on speed, you had to have a wild rise time, and you had to have wild slew rates, so many did just that. But at one point, ONLY AD could claim that their SETTLING TIME was not 2,000 or 1,500 nS as 99% of them had, but they had 90 nS of settling time for 0.01%, or TEN TIMES shorter than anybody else, who usually declared settling times for 0.1%. For 0.1%, they needed something like 55...45 nS, which is around 27 TIMES faster than anybody else. I would call that a quantum leap.

They simply provided better symmetry of square wave rise and fall. It looked much more like sa square wave.

The first inkling I got from OP275. In my viw, this is one of the best audio chips of all time. And try as many times with any other op amp you care to name, but you will always get the best overall performance from any Philips or Marantz CD player when you kick out that NJR junk and put in OP275, since then to these days. It's settling time is 200 nS for 0.1%, no longer impressive, but still at least 7 times shorter than with most others.

Playing with AD op amps, they never once failed to provide more coherent detail level and especially spatial information than any other competitor I have ever tiried (although I've tried many, of course I could never try them all out, so some reserve is advised). My own Yamaha CD player, for example, uses two AD826 op amps in lieu of NJR junk, and that after many, many trial runs with others.

Of course, this is not to say that one cannot make a really good op amp even with long settling times - much as I hate and can usually pick out BB 21xx op amps in many devices, I really love their 604/2604 op amps and usually quote them on any list of audio op amps one should use I make.

I freely admit to being an AD junkie. My entire stock of op amps is composed of AD op amps only, because to me, they still sound the best, and believe me, it's not because Walt Jung had his column, which I followed closely. If one remembers that AD op amps still suffer from the standard op amp failing, struggling with current, and if one adds a simple small signal current boost transistors (Motorola MPSA 56/06 or Siemens BC 639/640, etc), I know from personal experience that you could end up with an audio block which would give even John a run for his money.

May not better John's, Wave's and Thorsten's discrete work, but it will make them sweat to better it. And, of course, in terms of prices, it will come up best, if you can stomach the sound difference, which will probably be there, but it will be small, I guarantee it.

Symmetry accounts for much more than it is commonly credited with.

[1audio]

While slew rate is part of good settling time it takes a holistic approach to design to get really good settling times. Any stored energy will translate to longer settling times.

Keith's (KOJ) focus on asymmetric slew rates is due to a sensitivity to dc build up since audio waveforms are not symmetrical. Its less important today as much because digital has hard limits on the maximum rate of change at the input of a system as anything else (unless you chose to dispense with the reconstruction filter and like the IM contributions. . . ) I do remember opamps with slew rate claims based on full internal saturation, meaning the recovery was going to take a long time (poor settling times). I used the 3% THD frequency as a way to determine useful slew rate. Measuring the short settling times is a real bitch to do.

Keith's place in Tarzana was a nice little bungalow (with his pipe organ stuffed into that small living room) and the "space matrix" which could pull amazing spatial information from conventional recordings. I still have not heard as good a solution.

[dvv]

@1audio

Your remark of full saturation slew rate measuring makes me wonder about slew rate specs in general - what is declared as slew rate may in fact be more than what one would really want, because I strongly doubt anyone wants full saturation of any part of his circuit.

In other words, if the specs say 15 V/uS, it could well be that in fact this is more like say 10 V/uS without saturation.

Completely agreed on the wholistic design remark.

[nigel pearson]

I was always unhappy about the idea of an over engineered VAS in amplifiers which claimed to be so fast as to ignore the asymmetry . The main reason is it makes other aspects hard to design . The PP VAS of the Hitachi MOSFET and many op amps a better idea . The objection to PP VAS is that there are two independent routes for current flow . OK if making a mass produced amplifier the 2 minutes work to optimize the amp a problem ( really ? ) . Even the un-tweaked Hitachi is good . The tweaks are improved current mirror and verifying the 6n8 and 12 K VAS No1 compensator at 50 kHz is optimum ( distortion ) .

The slewing of the Hitachi can be improved . However real music will not be a problem . It is a nice compromise . Some over look how it's two VAS's form a symmetrical constant voltage clamp on the LTP input . That gives a balance factor of 2% which is fine .

The standard single VAS is like a bicycle with one crank . I have tried it and it works OK for either . Two much better .

[bcarso]

Originally Posted by 1audio

While slew rate is part of good settling time it takes a holistic approach to design to get really good settling times. Any stored energy will translate to longer settling times.

Keith's (KOJ) focus on asymmetric slew rates is due to a sensitivity to dc build up since audio waveforms are not symmetrical. Its less important today as much because digital has hard limits on the maximum rate of change at the input of a system as anything else (unless you chose to dispense with the reconstruction filter and like the IM contributions. . . ) I do remember opamps with slew rate claims based on full internal saturation, meaning the recovery was going to take a long time (poor settling times). I used the 3% THD frequency as a way to determine useful slew rate. Measuring the short settling times is a real bitch to do.

Keith's place in Tarzana was a nice little bungalow (with his pipe organ stuffed into that small living room) and the "space matrix" which could pull amazing spatial information from conventional recordings. I still have not heard as good a solution.

Another aspect of d.c. buildup as you call it comes in with second harmonic distortion, which so many refer to cavalierly as "benign". But for other than pathological cases, there is always a d.c. shift as well as the actual 2f energy. And then IM products are at simple sum and difference frequencies, thus high frequency energy can produce a difference that falls in regions of highest aural acuity.

If one confines listening material to single instruments or voices, a little low-order HD amounts to, perhaps, a perceptible timbral shift, and the aforementioned d.c. shift may be just noticeable (if always highpassed out rapidly by other aspects of the system). But for more complex textures the congestion sets in.

I once remarked to KOJ that, for sampled-data systems, you had the luxury of just waiting to look at the settled signal, but in audio how one "got there" was probably important as well.

And yes, settling time to high accuracy is a biatch to measure.

dvv, there is an old Analog Dialogue with a very good introduction to settling time and the requirements for its achievement in opamps. Probably it's available online. They have been at this for a while Pease also did some good work with Philbrick on test fixtures.

Brad

[dvv]

Originally Posted by bcarso

...
dvv, there is an old Analog Dialogue with a very good introduction to settling time and the requirements for its achievement in opamps. Probably it's available online. They have been at this for a while Pease also did some good work with Philbrick on test fixtures.

Brad

Good pointer - thank you, Brad, I will take a look.

I prefer to read up on such matters rather than rely on my own experiences only, even if they are primary.

And I do agree, they HAVE been at it for quite some time. Obviously.

[nigel pearson]

The DC component of second harmonic is a very good point . I never stopped to think how it gets there if a transistor amplifier in detail ( LTP balance and VAS usually said ) . My one legged cyclist again ? I am sure second harmonic is benign . The one legged cyclist not . The point is a double VAS both sources and sinks current equally like a 180 degree twin cylinder engine . The single cylinder ( leg ) more relies on any flywheel effect . I wonder has a choke ever been used for CCS of a single VAS ? Also is a bootstrap better than a standard CCS if so ?

[gpapag]

Originally Posted by bcarso

there is an old Analog Dialogue with a very good introduction to settling time and the requirements for its achievement in opamps. Probably it's available online. They have been at this for a while Pease also did some good work with Philbrick on test fixtures.

Brad

Is this the one Brad?

http://www.analog.com/library/analog.../cd/vol4n1.pdf

(In any case, thank you for pointing to these publications)

George