How inexpensive could a pre-pro be? (1 Viewer)

[chung]

I'm actually quite surprised if an audio enthusiasts claims they can't hear differences in CD players, as in exteme examples it's really rather overt.

My standard response when people say they can hear differences between DAC's is "So"? I am much more concerned about differences between speakers, power amps, and the quality of the sound mastering. I consider myself lucky that I am not at all bothered by the differences between DAC's, but I believe some of us have much more acute sense of hearing.

 

[chung]

Oversampling was specifically implemented to address electronic jitter. Oversampling can not cure mechanical jitter however.

I plead ignorance. Please explain to me how oversampling is implemented to address jitter. While you are at it, explain to me what mechanical jitter means.

 

[Craig_Kg]

Sorry Chung, you've lost me with your description of oversampling reducing aliasing distortion in DACs. All the documentation that I have seen relating to oversampling shows the oversampling being applied to increase the timing accuracy for determining the edge transitions for the output from the transport to reduce jitter.

I can't see how reconstructing the waveform at a higher rate than the recording sampling interval makes any difference to the output waveform. Does the DAC create intermediate interpolations between the recorded values to try and raise the resolution of the output? Ringing from the filtering required at recording is still going to creep in for the frequencies approaching the sampling cutoff (any intermediate oversampling values in recording at a higher rate will be lost in the 44.1kHz master).

Did you read what a posted about the effect of phase on the sonic image constructed by the brain? This is why jitter and ringing can be more of a problem than wow and flutter and the lower frequency limits of vinyl.

BTW I agree with your comments re interconnects and I can barely hear most of the problems that I am describing but know of the theoretical effects. I also prefer CD.

 

[Larry B]

Chung:

Quote:

I can't speak to the magnitude of differences in turntables, as I have not listened to many. However, I do know that the difference in CD players is enormous. I strongly suggest you listen to an entry level CD player (perhaps a JVC, or something of similar ilk) and compare it to a top-of-the-line Linn or Levinson. Of course, the better your associated equipment, the greater will be the perceived difference between the players.
Larry

 

[MatthewJ S]

O.k. SO, if we get a good transport,great amps and speakers,and a pre-pro with up to date D to A converters ...how cheap could Yamaha build a resonably good pre-pro for?..many think @ $400...if you build it they (or at least my cheap ass) will come!

 

[Larry B]

Matthew:

O.k. SO, if we get a good transport,great amps and speakers,and a pre-pro with up to date D to A converters ...how cheap could Yamaha build a resonably good pre-pro
for?..many think @ $400...if you build it they (or at least my cheap ass) will come!

Well, that sure brings this thread back on track. (Although I found the digressions more interesting. )
Larry

 

[Saurav]

Assuming your statement is true, how is that going to show up at the DAC's output, which is sampled by a clock phase-locked to a crystal reference?

Actually, according to posts I've seen by people who've actually worked at companies making CD players/receivers/DACs, that statement is true for less than 10% of commercially available DAC implementations. Most DACs regenerate the clock from the input digital stream using a PLL. Or maybe I don't understand what you're saying - what do you mean by a DAC's output being sampled by a clock? Why would a DACs output, which is analog, be sampled?

Anyway, in theory, it is possible to virtually eliminate the effects of all upstream jitter simply by reading the bits into a buffer and then re-clocking them out using a crystal oscillator, and then feeding that stream to the DAC. This technique is very commonly used in the telecom and datacom worlds. However, to the best of my knowledge, very few CD players/DACs use any such mechanism.

 

[Larry B]

Saurav:

Here's a partial description of the Mark Levinson No. 31.5 transport which may be relevant:

"But the Nº 31.5 goes much further than conventional electrical and mechanical isolation. Using a highly refined version of Madrigal's proprietary Closed-Loop Jitter-Reduction™ (CLJR™) system, the Nº 31.5 actually improves the quality of the digital signal before passing it along to the digital processor. The CLJR system uses a small memory buffer in conjunction with the reference clock discussed above. Operating at 256x the sampling rate, this precision clock controls precisely when each successive bit of information is allowed to leave the Nº 31.5 on its way to the digital processor and ultimate conversion to analog. To ensure that the next bit of information is ready to go at its appointed time, the transport mechanism is slaved to the needs of a "perfect" output (as defined by the reference clock). A 2x industrial CD-ROM mechanism is used to read the data on the disc, due to its greater ability to respond quickly to the needs of the output."

Larry

 

[Saurav]

That's interesting, especially the fact that the transport is slaved to the DAC, instead of the other way round (which is more common in CD players). I read of a Linn transport-DAC combination where they had the digital data line running between them, and a separate clock connection through which the DAC fed a clock back to the transport. Apparently, doing this helps reduce (or remove) jitter introduced by the motors driving the CD spindle and the servo motors controlling the laser assembly.

A 2x CD-ROM... I wonder how many other audio manufacturers use ideas like that. That's the simplest way to eliminate one problem with data buffers, which is the need to wait for a little while until the buffer gets 50% full.

 

[Larry B]

Saurav:
I guess there's a reason why Levinson products sound as good as they do (and cost as much as they do ).
Larry

 

[Larry B]

Saurav:
You might also enjoy reading John Atkinson's review of the Levinson 31.5 transport:
http://www.stereophile.com/showarchives.cgi?356
Larry

 

[chung]

Craig_Kg:

I can't see how reconstructing the waveform at a higher rate than the recording sampling interval makes any difference to the output waveform. Does the DAC create intermediate interpolations between the recorded values to try and raise the resolution of the output? Ringing from the filtering required at recording is still going to creep in for the frequencies approaching the sampling cutoff (any intermediate oversampling values in recording at a higher rate will be lost in the 44.1kHz master).

You might want to read another thread on this forum, I think it was called something like 96KHz DAC vs 192KHz DAC's. Someone tried to explain oversampling with diagrams, and those may be helpful if you don't fully understand oversampling.

One intuitive way of looking at oversampling: If you do not have oversampling, the DAC's output changes every 22.7 microsecs. The filter smoothes out that change (connects those samples up) so that there is all the signal stays in the 20-20KHz band. Now, with 4X oversampling, for instance, the DAC's output changes every 5.7 microsec. These samples are much closer in time, therefore the filter has a much easier job connecting those samples together.

Ringing from the filter comes from the phase response of the filter not being linear (or the group delay changes with frequency). If the filter does not need to have a steep slope, one can more easily design a filter that has less group delay variations and therefore rings much less. Ringing refers to the response of the filter to a step change at its input.

In a similar way, oversampling at the input to an ADC reduces ringing of the anti-aliasing filter. Note that ringing is not an inherent by-product of conversion, but it is a result of the anti-aliasing filter.

Ideally you can design a non-oversampling system that has the exact performance specified by the CD format. But it is more difficult to do so. Oversampling does not improve the inherent accuracy of the CD format, but makes it easier to implement.

There are many good references on oversampling on the web. This is a subject that has been thoroughly studied since the late '60's.

 

[chung]

On the contrary my friend, you hear it every time you listen to a CD.

Larry, I don't really understand why people are obsessed with jitter at the output of the DAC. These things are not important. They are only important if you BELIEVE they are important. One phenomenon in "high-end" audio is that small differences get blown way out of proportion, and people pay mightily for the small differences.

No testing that I know of has correlated measurements of jitter at the output of the DAC to sonic, audible differeneces. It is all speculation.

On the other hand, imperfections of vinyl equipment are very well known and understood. You have your wow-and-flutter, tracking force and the centrifugal force imbalance causing distortion, surface noise, huge sensitivity to loading of cartridge (impedance seen by cartridge), vulnerability to dust/oil, deviations from RIAA specs., etc. These are much larger imperfections than jitter could ever be.

Those who prefer vinyl LOVE THE VINYL SOUND. It is OK to love that vinyl sound, just like it's OK for someone to love the tube sound. But understand that it has nothing to do with accuracy. High Fidelity should be about accuracy, otherwise it's just one man's taste against another's.

 

[chung]

Most DACs regenerate the clock from the input digital stream using a PLL. Or maybe I don't understand what you're saying - what do you mean by a DAC's output being sampled by a clock? Why would a DACs output, which is analog, be sampled?

Larry:

The raw data from the CD drive contains jitter and other errors. That data is read into the digital system of the player which resamples the data (therefore resynchronizing the data and removing jitter), applies error-correction and digital filtering (with or without oversampling) and then clocks the data out to the DAC's. The DAC's do not regenerate the clock. The DAC's are clocked by the digital system that generates a clock phase-locked to a reference. The output of the DAC is in sampled form, because it changes in response to the data it receives at the instant the incoming clock pulse is received. Then the low-pass filter smoothes out the samples to give you the 20Hz-20KHz audio. Jitter from the reading process can also be removed at the transport, by synchronizing the transport with a crystal reference. I do not think that is necessary, but obviously some companies do that to obtain a "perceived" sonic advantage.

Hey, if someone thinks that the Linn CD player is the way to go and is willing to pay for it, that is OK with me. I am just saying that it is not going to make a difference that is anywhere close to what you pay. However, money takes on different value for different people. For me, putting money on speakers is a much better deal.

 

[Larry B]

Chung:

Once again, I respectfully disagree with much of what you say.

On the other hand, imperfections of vinyl equipment are very well known and understood. You have your wow-and-flutter, tracking force and the centrifugal force

imbalance causing distortion, surface noise, huge sensitivity to loading of cartridge (impedance seen by cartridge), vulnerability to dust/oil, deviations from RIAA specs., etc. These are much larger imperfections than jitter could ever be. Those who prefer vinyl LOVE THE VINYL SOUND. It is OK to love that vinyl sound, just like it's OK for someone to love the tube sound. But understand that it has nothing to do with accuracy. High Fidelity should be about accuracy, otherwise it's just one man's taste against another's.

I disagree (as do many others) that the imperfections in vinyl playback "are much larger imperfections than jitter could ever be." Perhaps to a machine, but not to the human ear. Out of curiosity, do you audition equipment by listening, or by reading specs?

And last, while I agree that High Fidelity is (literally) about accuracy, I most definitely do not agree that the mechanical, tinny, digital sound of CDs is more accurate. If live music sounded like most CD players, I would have very little interest in listening. But then again, you thought the CD players of the early 1980's were terrific....

Larry

 

[chung]

Larry:
I know I am not going to win arguing against one who so adamantly prefers vinyl
Interesting how this thread morphs to a vinyl-vs-CD thread.

 

[Larry B]

Chung:

Let's keep vinyl out of the discussion.

Do you have any experience with stand-alone transports? If so, do you think they all sound alike? More precisely, do you believe that a $200 CD player, if used as a transport, will sound pretty much the same as a Mark Levinson reference level transport?

I have done this kind of comparison and, to my ear, the difference is substantial. To what other than jitter can this be attributed?

Larry

P.S. If you've never done such a comparison, I suggest you consider doing so.

P.P.S. Do you think all measurable deficiencies in playback are of equal importance to our ear/brain?

 

[Saurav]

Regarding accuracy... I feel that my vinyl setup more accurately conveys what I'm interested in the music, which is the emotional content. My CD setup sounds dull and boring in comparision. So, you're right, it's all about a person's tastes, and I think it's also about what you're trying to achieve with your system. I don't care for flat frequency response if the presentation doesn't move me emotionally. Other people have different priorities.

I disagree (as do many others) that the imperfections in vinyl playback "are much larger imperfections than jitter could ever be."

Actually, I agree with Chung here. If you're comparing the magnitude of the distortion, IMO vinyl is nowhere close to digital in terms of accuracy. However, even with its measurably larger errors, I think vinyl gets some things right that CDs do not, and to me those are the things that are important in the music.

Here's a great example which illustrates what I'm trying to say. There are some turntables which employ feedback mechanisms to control the rotation speed of the platter. In essence, the control electronics constantly checks the speed of the platter, and slows it down or speeds it up to correct for errors. This technology gives vastly superior wow and flutter performance figures than conventional belt or direct drive turntables. As a result, when these turntables were first introduced, they were met with great enthusiasm, because it was quite obvious to everyone that these performed better than turntables with conventional technology.

However, after living with this technology and listening to it for a while, people realized that it had a critical flaw. What was happening was, the electronics that controlled the platter's speed was always searching for the correct operating point - it was always speeding up, correcting the error and slowing down, correcting the error and speeding up again, and so on. This happened quickly enough and with a small enough magnitude that the wow and flutter measurements (which are averaged out over time) were better. However, this constant speed change obviously had an effect on the music - the timing and rhythym in the music weren't reproduced accurately. And it turned out that human hearing is pretty sensitive to this missing "swing" in the music.

Anyway... someone as well-versed with technology as chung is probably well aware of what I'm talking about, so this isn't meant to be a condescending discourse in any way. I'm just trying to illustrate the fact that something that measures better doesn't always sound better. 30 years ago, I'm sure we believed that we knew what to measure. Today, we know that sound of our ideas back then were pretty far off. I'm fairly confident that 20 years into the future, we will consider some of our current ideas laughable.

 

[Saurav]

Interesting how this thread morphs to a vinyl-vs-CD thread.

Yup. Maybe we should throw in some tube vs. SS and powered towers vs. subwoofers too, just for good measure, and then make this the "mother of all arguments" thread. Of course, any thread with a title like that has to have some "all cables sound the same", or it doesn't deserve to be called the mother of anything

 

[Larry B]

Saurav:

30 years ago, I'm sure we believed that we knew what to measure. Today, we know that sound of our ideas back then were pretty far off. I'm fairly confident that 20 years into the future, we will consider some of our current

ideas laughable.

Well said. As an aside, this humbling point of view is shared by many in the field of medical research, as well.