TC-7510 question

[Phileas]

I recently bought a TC-7510 (it sounds pretty good).

This forum seems to contain a lot of shared knowledge about it and I'm curious about a couple of claims made on the Beresford web site:
"It reclocks and resamples incoming digital data using its own inbuilt jitter free clock in order to negate jitter in the original signal. The actual Digital to Analog conversion process takes place at 352.8KHz for a 16 bit/44.1KHz CD audio signal, and 384KHz for DVD audio."

Firstly, is there such a thing as a jitter free clock? There are no measurements quoted on the site and I'm assuming it doesn't totally 'negate' the jitter in the incoming signal.

Secondly, are there DAC chips which convert at 384kHz or does this statement refer to 8x oversampling? (Or am I confused?)

[roscoeiii]

True, "jitter-free" would imply an escape from the laws of physics, but I think the writers assume that you will automatically insert the words "for all intents and purposes relevant to the task at hand." That said, I would love to see some John Atkinson (Stereophile magazine) style measurements of the 7520 or any other DAC.

True, we shouldn't buy on measurements alone, but they can be useful data to have as you are weighing your options.

[Phileas]

I would love to see some John Atkinson (Stereophile magazine) style measurements of the 7520 or any other DAC.

True, we shouldn't buy on measurements alone, but they can be useful data to have as you are weighing your options.

I'm not an electronics specialist but I like the idea of a well-engineered product which to me implies a certain amount of objective measurement.

As I said, I own a TC-7510. I also have a Benchmark DAC1. In my (wholly inadequate) listening comparisons, I couldn't detect a significant difference between them (although the DAC1 was a significant step up from my Marantz CD6000 OSE LE).

So, although the TC-7510 is clearly a well designed (internally) product, the slightly confusing information on the company website might tend to put seeds of doubt in a prospective purchaser's mind.
It was only by doing research on internet forums like this that persuaded me to buy one.

Even then, I may have made a mistake by buying the TC-7510 instead of the TC-7520 because I assumed the only difference was the USB interface -apparently the headphone amp is also a significant upgrade. But that's partly my fault for not reading the available information carefully.

[StanleyB]

Firstly, is there such a thing as a jitter free clock? There are no measurements quoted on the site and I'm assuming it doesn't totally 'negate' the jitter in the incoming signal.

Secondly, are there DAC chips which convert at 384kHz or does this statement refer to 8x oversampling? (Or am I confused?)

The clock is jitter free. 0 = 0, so it is pointless to quote a measurement of 0%. The jitter of the clock and the jitter of the incoming signal are two different things.

DAC chips can convert at all kind of frequencies. Oversampling chips like the one fitted to the TC-75xx range can be set at the design stage to convert at frequencies up to 769KHz. Unfortunately at that frequency it will only accept 24bit/48KHz audio data at its input. I choose 384KHz since that will accept 24/96 audio for decoding.

The incoming frequency of the data and the conversion frequency are two different things.
In the case of say the DacMagic, their conversion frequency is 192KHz for every incoming data frequency.
In the case of the TC-75xx Audio CD is converted at the higher 352.8KHz and DVD at 384KHz.

As for the observations with regards to comparisons with the DAC1, I have been pointing that out for years.

Stan

[Phileas]

The clock is jitter free. 0 = 0, so it is pointless to quote a measurement of 0%.

Ah, but then it might be argued that it's pointless to mention that it's jitter-free unless some clocks aren't.

DAC chips can convert at all kind of frequencies. Oversampling chips like the one fitted to the TC-75xx range can be set at the design stage to convert at frequencies up to 769KHz

I asked about this because the Benchmark engineer (Elias Gwinn on a thread over at Head-Fi) said that there aren't any chips which convert well at 192kHz, but I'm probably misunderstanding somewhere.

As for the observations with regards to comparisons with the DAC1, I have been pointing that out for years.

The great thing with the DAC1, of course, is that it performs equally regardless of the amount of jitter on the input and Benchmark publish test results which (apparently) demonstrate that. It's nice to know that when connecting it to various sources (even if the audibility of jitter is slightly controversial).

Phileas

[StanleyB]

Ah, but then it might be argued that it's pointless to mention that it's jitter-free unless some clocks aren't.

Well I suppose a deviation of a few seconds over a year would make a watch powered by a jitter free clock not accurate enough. How many 0's would you consider an appropriate figure after the comma before an accuracy of 100% can be quoted? 1, 6, 9, 12?

I asked about this because the Benchmark engineer (Elias Gwinn on a thread over at Head-Fi) said that there aren't any chips which convert well at 192kHz, but I'm probably misunderstanding somewhere.

Which is why I am perplexed at the use of that frequency by Cambridge.

Stan

[StanleyB]

That said, I would love to see some John Atkinson (Stereophile magazine) style measurements of the 7520 or any other DAC.

HIFI Choice did such a measurement test in their Feb 2009 issue and the TC-7510 was a close match to the Lavry10 and out performed the Apogee.

True, we shouldn't buy on measurements alone, but they can be useful data to have as you are weighing your options.

Do you put more trust on measurements displayed on a CRT or LCD display, than those measured by your ears? If that's the case, you won't like the sound of an Aston or Ferrari with their ICE switched off.

Stan

[Phileas]

Well I suppose a deviation of a few seconds over a year would make a watch powered by a jitter free clock not accurate enough. How many 0's would you consider an appropriate figure after the comma before an accuracy of 100% can be quoted? 1, 6, 9, 12?

What I meant was that if any half decent clock is essentially jitter-free, why mention it? It's almost like mentioning that the on-off switch is error free.

On the subject of conversion rates, here is a quote from the aforementioned Head-Fi thread (http://www.head-fi.org/forums/f46/be...r#post2971892):

"I would like to expound on why 192 kHz conversion is not a good idea.

The filters in a D-A chip ideally pass all audio below the Nyquist frequency and block (filter) all audio above the Nyquist frequency. In reality, however, there will be some audio below the Nyquist that is being filtered some, and there will be some audio above the Nyquist which is not filtered enough. The latter is very dangerous because those frequencies will be aliased and cause distortion.

Here's the problem with 192 kHz: the filter used for 192 kHz is of far less quality. This is true of ALL D/A chips on the market. What happens is this: the filter cut-off becomes less defined, causing audio below Nyquist to be attenuated. And, more importantly, AUDIO ABOVE NYQUIST IS NOT FULLY ATTENUATED!! The filter does not do its job as well at 192 kHz.

Another 'real-life' limitation to these filters is amplitude ripple. This means that the audio below Nyquists will have ripples in amplitude across the frequency spectrum. This is equivalent to inaccurate frequency response. This is also something that happens in all D-to-A chips, some more so then others.

The problem with 192 kHz: the ripples in amplitude become much more exaggerated when filtering 192 kHz signals. Consequently, the frequency response is much less accurate and distortion goes up.

This is why most all converter designers and recording engineers don't recommend 192 kHz. The chip technology has not provided the means to effectively convert 192 kHz without these problems.

So, the trade-off for the extra analog bandwidth is an increase in aliasing and frequency-response distortion. Although some people may 'enjoy' listening to 192 kHz more then lower rates, it is not as accurate, objectively speaking.

Thanks,
Elias"

Phileas

[StanleyB]

What I meant was that if any half decent clock is essentially jitter-free, why mention it? It's almost like mentioning that the on-off switch is error free.

. Your logic defies gravity. on-off switches are not error free. As an electronic repair engineer I replaced many on-off switches that had developed errors in their operation.

On the subject of conversion rates, here is a quote from the aforementioned Head-Fi thread (http://www.head-fi.org/forums/f46/be...r#post2971892):

[I]"I would like to expound on why 192 kHz conversion is not a good idea.

The filters in a D-A chip ideally pass all audio below the Nyquist frequency and block (filter) all audio above the Nyquist frequency. In reality, however, there will be some audio below the Nyquist that is being filtered some, and there will be some audio above the Nyquist which is not filtered enough. The latter is very dangerous because those frequencies will be aliased and cause distortion.

As I mentioned, I don't use 192KHz. I use a far higher frequency for precisely the reasons mentioned. By converting at a higher frequency I am able to filter at a far higher frequency and take care of the more dangerous aliased frequencies in that region that cause distortions in other, often more expensive, DACs.

Stan

Stan

[Phileas]

. Your logic defies gravity. on-off switches are not error free. As an electronic repair engineer I replaced many on-off switches that had developed errors in their operation.

OK, sorry. I'm guilty of forgetting what I wrote in my original post.

I wrote:"Firstly, is there such a thing as a jitter free clock? There are no measurements quoted on the site and I'm assuming it doesn't totally 'negate' the jitter in the incoming signal."

I don't think I meant (it was a long time ago) that I wanted a measurement of the jitter of the clock, it was just jitter attenuation as a whole I was interested in.

:
As I mentioned, I don't use 192KHz. I use a far higher frequency for precisely the reasons mentioned. By converting at a higher frequency I am able to filter at a far higher frequency and take care of the more dangerous aliased frequencies in that region that cause distortions in other, often more expensive, DACs.

Stan

Sorry to sound obtuse, but the way I interpreted what Elias said is they chose 110kHz because there are no chips available which convert above that rate without certain compromises which they preferred not to make.
In another post in the same thread, he says that when such a chip becomes available, they'll be incorporating it into a new design as soon as possible.

I'm not trying to question the design of your DACs, I just like to understand things I read. If a reply would be too lengthy or reveal any trade secrets then feel free not to answer.

Phileas