The biggest difference I hear between digital and analog

[opus111]

While I am sympathetic to what you say, a well designed amp, in the first place, will not slew at audio frequencies (wanna know how many of your favorite recordings from the sixties and seventies were on mixers with slew rates of 10Usec or less....a bunch) but I am not all together certain that extended bandwidth on the output is needed if you get the real audible audio band right in the first place.

A lot to address here - firstly do you have a falsifiable definition of 'well designed' ? Does it mean 'designed so that on listening, the vinyl guys will love it' ? Or does it mean 'meets traditional THD and SNR expectations' ?

Secondly, I wasn't meaning hard slew limiting which is why I used the scare quotes and said others use that phrase. But slewing induced distortion starts to occur well before the datasheet slew limit is reached. Check out any opamp datasheet which shows THD20 and compare that with THD1.

 

[Phelonious Ponk]

Tim,

You assume well. Most of us only report aspects we notice in LP reproduction. I am not an expert in audio design, I can not give you an exact explanation why and how some equipment manages it. I can guess that there is some manipulation of the signals that will enhance the music signal and separate it from noise exploiting the electrical properties of the mechanical noise of vinyl. It will surely be based in some well known psychoacoustic principle.

I have learned long ago that we have no good explanation for most things we observe in audio. I do not know why a Pass XS amplifier sounds different from a Soulution or a Bryston. But just because I can not explain it will not prevent me from enjoying their differences.

Yeah, here's the thing. Back in the real analog days, when it was the leading audio technology and, therefore, drew the best engineers, those engineers, some really, really brilliant ones, set themselves on task of eliminating, or at least substantially reducing, tape noise without audibly impacting the signal. Tape noise, of course, is much less random, much more predictable and more easily isolated than record surface noise. It was less of a challenge, but they couldn't pull it off. The best noise reduction was pretty good, but it was audible. Yet boutique high-end designers have not only pulled it off, but almost without trying? It happened not as a result of an entire recording and playback industry putting their substantial weight against a specific problem but as a side benefit of one man's preamp design?

I don't know what you hear, micro. But I know what it is not.

Tim

 

[Phelonious Ponk]

I think the technical explanation probably has something to do with overload performance, or what some would call 'slew limiting'. Pops and clicks have energy beyond the audio band - this excess HF energy can intermodulate with the in band stuff, giving rise to low-level grunge. A good phono preamp has extremely good linearity, even above 20kHz and the absence of low-level IMD shows itself when listening giving a natural, non-fatiguing sound.

Perhaps you have another, less technical explanation? I don't see how this one explains the reduction of the volume of noise in the audio band without reducing the volume of other content in the same frequencies as the noise. I must be missing something.

Tim

 

[Phelonious Ponk]

A lot to address here - firstly do you have a falsifiable definition of 'well designed' ? Does it mean 'designed so that on listening, the vinyl guys will love it' ? Or does it mean 'meets traditional THD and SNR expectations' ?

Secondly, I wasn't meaning hard slew limiting which is why I used the scare quotes and said others use that phrase. But slewing induced distortion starts to occur well before the datasheet slew limit is reached. Check out any opamp datasheet which shows THD20 and compare that with THD1.

Perhaps this is the less technical explanation?

Tim

 

[opus111]

Perhaps you have another, less technical explanation? I don't see how this one explains the reduction of the volume of noise in the audio band without reducing the volume of other content in the same frequencies as the noise. I must be missing something.

Yes you are missing something, but I agree my explanation was very 'bare bones' there. So let me add a little more meat to see where it gets us. The noise in the audio band is broad band IMD - from the many discrete tones of music come countless other small tones by virtue of IMD. They're all over the band because they arise from sum and difference frequencies between the music and the out of band pops and clicks. Mostly they'll be difference frequencies because the pop and click energy is above 20kHz so it has to 'fold down' to become audible. So then, for example a 15k tone beats with a 25k tone to give a 10k IMD product.

Any better now?

 

[opus111]

Perhaps this is the less technical explanation?

Does that seem less technical to you then?

 

[NorthStar]

-- Tim brought an interesting 'analog' point: noise reduction systems for tapes.
...Dolby, Dolby B, Dolby C, Dolby S, Dolby HX Pro, DBX, etc.

We don't talk no more about analog in respect to tapes .... Where's the 'nostalgic' love now? :b

________________

- Analog: The improved past, with today's extravagances; mainly TTs & all that is related to them.
- Digital: The yet to be still improved future, today. ...CDPs (SACD) and Hi-res audio servers.

 

[Phelonious Ponk]

Yes you are missing something, but I agree my explanation was very 'bare bones' there. So let me add a little more meat to see where it gets us. The noise in the audio band is broad band IMD - from the many discrete tones of music come countless other small tones by virtue of IMD. They're all over the band because they arise from sum and difference frequencies between the music and the out of band pops and clicks. Mostly they'll be difference frequencies because the pop and click energy is above 20kHz so it has to 'fold down' to become audible. So then, for example a 15k tone beats with a 25k tone to give a 10k IMD product.

Any better now?

Maybe. Bear with me as I try to wrap my head around it -- Any tones in the signal -- pops, noise, music -- can interact, generating other non-linear tones (noise) all over the band: IMD. So a component with very low IMD, while it cannot reduce the amplitude of the surface noise of the record without reducing the amplitude of the same frequency bands of music in music, can reduce the IMD generated by those pops and cracks? Am I with you so far? I still have questions:

If the designer hasn't found some way to specifically target the surface noises, and has merely designed a pre with remarkably low IMD across the audible band, how is it that listeners hear the huge, targeted reduction of not only isolated bands, but of specific noise events (surface noises)? Wouldn't this huge improvement in linearity effect the entire signal? Wouldn't its relative impact on record surface noise remain equal?

If it is just the linearity, the low IMD of the components that are creating this "noise reduction," is this not measurable? Demonstrable? Haven't we understood for many years that low IMD is a good thing? Aren't we at the point where it is extremely low in most quality audio? Are we still making HUGE improvements? Really? And are they measurably, hugely, better in very expensive phono preamps than in every other class of component where low IMD is beneficial? That would explain how one could change phono preamps and suddenly hear this huge difference. I'm not sure what else can.

Tim

 

[microstrip]

Yeah, here's the thing. Back in the real analog days, when it was the leading audio technology and, therefore, drew the best engineers, those engineers, some really, really brilliant ones, set themselves on task of eliminating, or at least substantially reducing, tape noise without audibly impacting the signal. Tape noise, of course, is much less random, much more predictable and more easily isolated than record surface noise. It was less of a challenge, but they couldn't pull it off. The best noise reduction was pretty good, but it was audible. Yet boutique high-end designers have not only pulled it off, but almost without trying? It happened not as a result of an entire recording and playback industry putting their substantial weight against a specific problem but as a side benefit of one man's preamp design?

I don't know what you hear, micro. But I know what it is not.

Tim

Yes, Tim, the boutique people manage to do it. You will find it everywhere - speakers having a lower noise floor, cables changing the perception of noise. But it was not done without trying - most of them spent a lifetime perfecting their products for our delight.
I can not understand why you want to mix the recording industry in this debate - we are debating specifics of the playback system of existing LP recordings. And it is not a debate of one man's preamp design - happily many have similar properties. One of them even uses J-FETs in the input and tubes!

 

[opus111]

Maybe. Bear with me as I try to wrap my head around it -- Any tones in the signal -- pops, noise, music -- can interact, generating other non-linear tones (noise) all over the band: IMD. So a component with very low IMD, while it cannot reduce the amplitude of the surface noise of the record without reducing the amplitude of the same frequency bands of music in music, can reduce the IMD generated by those pops and cracks? Am I with you so far?

Yep, seems like you grasped it.

I still have questions:

If the designer hasn't found some way to specifically target the surface noises, and has merely designed a pre with remarkably low IMD across the audible band, how is it that listeners hear the huge, targeted reduction of not only isolated bands, but of specific noise events (surface noises)? Wouldn't this huge improvement in linearity effect the entire signal? Wouldn't its relative impact on record surface noise remain equal?

I'm not with you on this. Most preamps (the mainstream, based as they are on opamps) don't have great IMD linearity so the surface noise they're generating isn't the real surface noise, rather its an IMD induced grunge. I don't understand 'targeted reduction' here. There's a secondary effect which I haven't mentioned - surface noise is just lowish level pops and clicks, but there are the bigger pops and clicks which can easily overload (clip) a not-so-well-designed stage and exaggerate their effect.

The linearity improvement does indeed affect the whole signal, there's no way that it couldn't. So I'm perplexed by your questions - would you rephrase them?

If it is just the linearity, the low IMD of the components that are creating this "noise reduction," is this not measurable? Demonstrable?

In principle yes, for sure. In practice the measurement is tricky to make.

Haven't we understood for many years that low IMD is a good thing? Aren't we at the point where it is extremely low in most quality audio?

Yes I believe so to the first, no, I don't believe so to the second owing to lack of standardized measurements and easily available kit to make them. The IMD is not the kind of IMD covered by SMPTE and CCIR, those measurements don't cut it because they're measuring large signal non-linearity, not small.

Are we still making HUGE improvements? Really? And are they measurably, hugely, better in very expensive phono preamps than in every other class of component where low IMD is beneficial? That would explain how one could change phono preamps and suddenly hear this huge difference. I'm not sure what else can.

I'd not say, nor even suggest that price is a guarantee of low IMD at the signal levels which matter. Amps also suffer from low level IMD problems which I believe is one reason why SQ differences exist between them.

 

[asiufy]

I wish I could say the same. But when I think of the great listening sessions I have with my LPs of the hatART, SoulNote, BlackSaint and many others and compare them with the much inferior CDs we get of this recordings I am happy that my analog system has very little surface noise.

Much of my classic listening is carried in digital, but for other types of music, if a good condition LP is available I prefer the LP. I would like to know of someone saying that he has an excellent digital version of "Lamb Lies down on Broadway" or of "The Crime of the Century".

Microstrip,

You should listen to the remixed SACD of "The lamb", or better yet, the DSD files ripped to a good computer, hooked up to a proper DSD-capable DAC. The original is quite muddy, even on an original LP, and the remix clears up quite a bit, making everything crystal clear. And the SACD layer softens a little bit the effects of the aggressive compression using for the redbook and DVD-A layers.


alexandre

 

[Phelonious Ponk]

Don't be perplexed by some of my answers, Opus. It is merely lack of knowledge. I'm thrilled, that on balance, I appear to have grasped it.

Tim

 

[opus111]

Oh its not your answers Tim that perplex me, rather the questions. And being perplexed isn't uncomfortable for me, so don't fret over my being perplexed, its a regularly occurring state for me.

 

[Phelonious Ponk]

Yes, Tim, the boutique people manage to do it. You will find it everywhere - speakers having a lower noise floor, cables changing the perception of noise. But it was not done without trying - most of them spent a lifetime perfecting their products for our delight.
I can not understand why you want to mix the recording industry in this debate - we are debating specifics of the playback system of existing LP recordings. And it is not a debate of one man's preamp design - happily many have similar properties. One of them even uses J-FETs in the input and tubes!

Now that I understand what "it" is -- lowered IMD -- this is no mystery. Of course the boutique high end is far from alone in having lowered IMD. And by the way, I cannot understand how you cannot understand that the recording industry is inseparable from playback and that noise reduction is relevant to a discussion of reducing noise. But I digress....

Tim

 

[Phelonious Ponk]

Oh its not your answers Tim that perplex me, rather the questions. And being perplexed isn't uncomfortable for me, so don't fret over my being perplexed, its a regularly occurring state for me.

In this case, my questions were the only answers I had to offer. They are one in the same.

Tim

 

[microstrip]

Microstrip,

You should listen to the remixed SACD of "The lamb", or better yet, the DSD files ripped to a good computer, hooked up to a proper DSD-capable DAC. The original is quite muddy, even on an original LP, and the remix clears up quite a bit, making everything crystal clear. And the SACD layer softens a little bit the effects of the aggressive compression using for the redbook and DVD-A layers.


alexandre

Alexandre,

Thanks for your suggestion. However I was addressing CD, not the alternative digital formats. I currently do not own a SACD or DSD-capable DAC. There is currently not material enough that pleases my taste to justify my investment in these formats. IMHO for most music lovers the real choices are only two formats - the LP and the CD (16/44.1 either physical or virtual) if they want to enjoy new releases.

Anyway, I have looked for the SACD of "The Lamb ..." It seems to be sold out and became a collector item, people ask a lot for mint samples. No chance for me to evaluate it. But I never found my copy of the LP to sound muddy when a system was playing properly. Perhaps I got used to it, I have been listening to it since the year it was launched...

 

[microstrip]

Now that I understand what "it" is -- lowered IMD -- this is no mystery. (...)
Tim

Congratulations. For me it is not as easy as that. Anyway I take note you are now a believer in something that current usual techniques can not measure - the grunge and pops and clicks IMD. As most of my LPs are cleaned with a VPI17 and are usually in very good condition I am looking for something else.

 

[Atmasphere]

This is all very confusing. Just a post north of this one you told us "the choice of phono preamp can have a huge effect on surface noise." I think I do understand this. Let's bypass the hyperbole of "huge." All surface noise, of any size, is physical. It is the result of flaws in or on the surface of the disc (thus the name). The phono preamp receives that signal with the noise intact. If it has any effect on that surface noise, it can only be by making it louder by raising the volume of the frequencies of the noise, or making it softer by lower the volume of the frequencies of the noise. Phono preamps equalize and raise signal level that is given them at varying levels of purity and accuracy. Period. They have no noise reduction ability outside of those simple parameters. And what do we call it when specific frequencies are raised or lowered? Coloration. And yet you believe, at the same time that a phono preamp is lowering the volume of the frequencies of very audible surface noise, it is "lacking coloration." That's interesting.

I think the technical explanation probably has something to do with overload performance, or what some would call 'slew limiting'. Pops and clicks have energy beyond the audio band - this excess HF energy can intermodulate with the in band stuff, giving rise to low-level grunge. A good phono preamp has extremely good linearity, even above 20kHz and the absence of low-level IMD shows itself when listening giving a natural, non-fatiguing sound.

Tim, I have quoted you a response as it is part of the answer to your comments. But its not all- there is another factor.

Many preamps employ active EQ to do their job. The problem is that there is a propogation delay (the very measurable time it takes for a signal to move from input to output) in the phono (or tape) preamp. If active EQ is involved, the feedback signal will arrive slightly late at the input. Now at low frequencies this is not a problem, but as frequency goes up it becomes more and more pronounced (because the propagation delay is a fixed value). The phenomena varies from circuit to circuit depending on internal speed (slewing) of the circuit.

What can happen, and happens more than the industry really ever seems to talk about, is that a tick or a pop (which is a high frequency event due the sharp risetime they require) can 'ring' in the circuit. A simple way of looking at this is that the tick might appear, it gets amplified and fed back, but at the input the tick is already gone. But we now have a (weaker and negative) copy of the tick that is once again at the input of the preamp, offered by the feedback network. It has to make its way through the preamp too! This is a simple model of how this ringing can occur.

This problem seems to be exacerbated by poor high frequency response/slewing rate; of course there is a direct correlation to propogation delays in such circuits being longer.

The solution is to use no feedback (a circuit with no feedback is more stable than one with feedback and stability in this case is important) and passive EQ. You can still get the bandwidth (we spec 100KHz) but now the source of ringing has been eliminated. Since the circuit is zero feedback, methods other than feedback have to be employed to keep distortion down. (Keep in mind also that the preamp cannot be overloaded by the tick or pop; it must have very good IMD at high levels as previously implied.) The supply in particular must be quiet to prevent IMD. The tick or pop is then presented in its actual, non-emphasised amplitudes, occuring over a shorter period. The result is they are far less audible! I had this demonstrated to me in spades about 25 years ago; the difference can be quite dramatic, one where you would have thought the same record to be defective with one preamp and fine with another.

While I am sympathetic to what you say, a well designed amp, in the first place, will not slew at audio frequencies (wanna know how many of your favorite recordings from the sixties and seventies were on mixers with slew rates of 10Usec or less....a bunch) but I am not all together certain that extended bandwidth on the output is needed if you get the real audible audio band right in the first place.

Bandwidth and high slew rate are really one and the same. If you want a circuit to have a high slew rate, it will also be capable of wide bandwidth. You can't "get the real audible audio band right in the first place" if you don't have the bandwidth (as Holman was fond of pointing out decades ago), you need that to reproduce phase relationships correctly! 20Hz to 20KHz just will not do it. You need 2Hz to 200KHz to be able to reproduce all audible frequencies without phase shift. This is because group delays which are an artifact of the cutoff frequency will manifest 10X higher than the lower cutoff, and 10X less than the high cutoff.

 

[Phelonious Ponk]

Congratulations. For me it is not as easy as that. Anyway I take note you are now a believer in something that current usual techniques can not measure - the grunge and pops and clicks IMD. As most of my LPs are cleaned with a VPI17 and are usually in very good condition I am looking for something else.

I have always believed there are things we perceive that can't be measured. I believe this is mostly in the psychoacoustic realm you often refer to. I also happen to believe that the line between psychoacoustics and hearing what we expect to hear is a tiny bump in the road that we weave back and forth across all the time. This may be a great example. "It" is IMD. Commonly known. Measurable. Not often as thoroughly analyzed as we'd like, but not at all out of reach. Have the manufacturers of these uber-expensive pres shared the full body of what must have been exhaustive research, measurement and documentation leading to such breakthrough linearity as to result in such a HUGE audible difference? Or do you simply believe that they've done what so many others could not (without measurements even this is in question), because of your faith in their integrity, methodology, reputation? And could that faith be influenced by your perceptions of the brand? By the price? Would you believe it possible of a $50 phono pre? You don't have to answer this last question, but be honest with yourself.

Are we standing on the fine line between psycho acoustics and psychology? Or are we all over the line? In any case it makes me glad I have no records, no pops, no cracks, and no phono pre to exaggerate them. My the cost of limiting that exaggeration is dear!

You are as zealous a true believer in the church of high end as I have met, micro. I do not expect to change your mind. Ever. But I do enjoy the engagement. Thanks.

Tim

 

[microstrip]

I have always believed there are things we perceive that can't be measured. I believe this is mostly in the psychoacoustic realm you often refer to. I also happen to believe that the line between psychoacoustics and hearing what we expect to hear is a tiny bump in the road that we weave back and forth across all the time. This may be a great example. "It" is IMD. Commonly known. Measurable. Not often as thoroughly analyzed as we'd like, but not at all out of reach. Have the manufacturers of these uber-expensive pres shared the full body of what must have been exhaustive research, measurement and documentation leading to such breakthrough linearity to result in such a HUGE audible difference? Or do you simply believe that they've done what so many others could not (without measurements even this is in question), because of your faith in their integrity, methodology, reputation? And could that faith be influenced by your perceptions of the brand? By the price? Would you believe it possible of a $50 phono pre? You don't have to answer this last question, but be honest with yourself.

Are we standing on the line between psycho acoustics and expectations? Or are we all over it? In any case it makes me glad I have no records, no pops, no cracks, and no phono pre to exaggerate them.

You are as zealous a true believer in the church of high end as I have met, micro. I do not expect to change your mind. Ever. But I do enjoy the engagement. Thanks.

Tim

No Tim, I do not consider the high-end a religion. But I have the honesty and experience enough to know that we can not explain with our conventional mechanical and electrical knowledge all the high-end can offers us, and I do not believe in pseudo-science. I prefer to say I do not know why, and just acknowledge what I listen. The possibility of LP specific noise signals inter-modulating with other signals was studied long ago - people even used storage oscilloscopes to study these signals much before the digital oscilloscope was introduced. Even the 25 years old conrad johnson Premier 3 was specified as having less than .05% IMD.