[edmiston]

Hi James,

I understand the advantages of a one box player, but many of us have other sources (computer, music server, iPod with Wadia, etc that we may want to use as a source in addition to the cd player, and we are loathe to have to buy more than one dac.  Any chance of incorporating additional digital inputs in the Bcd-1?

Thanks,

Mark

[James Tanner]

Hi James,

I understand the advantages of a one box player, but many of us have other sources (computer, music server, iPod with Wadia, etc that we may want to use as a source in addition to the cd player, and we are loathe to have to buy more than one dac.  Any chance of incorporating additional digital inputs in the Bcd-1?

Thanks,

Mark

Hi Mark,

We are introducing an outboard DAC next week for mutilple sources. 

The idea with the CD Player was we wanted to optimize the digital quality by Clocking the Drive to the DAC to eliminate Jitter. Having a Digital input would mean that we would have to have another circuit to reclock and resample the incoming signal from the external drive etc.

james

[Sasha]

James,

Here is my dream single box CDP, there is no such product on the market, I may be one of a few that would like something like this, but anyway, this would be a killer product in my mind.
1.   Clock the drive to the DAC.
2.   Have a number of digital inputs (at least one of AES/EBU, SPDIF/BNC, SPDIF/RCA)
3.   Do upsampling/oversampling the way it is done in BDA-1, synchronously to 176.4K/192K depending on input sample frequency, with a twist described in #4.
4.   Extract clock from incoming signal only to keep internal DAC clock in sync with clock deviations from incoming signal, data is stored in buffer, clocked by internal clock that is adjusted at long time intervals, several seconds, so it is inaudible, and prevents buffer overrun/underrun, thus achieving high jitter immunity and independence from source clock.
5.   Have clock out to slave digital sources.
6.   Have high quality attenuation in analog domain after conversion.
7.   Have discrete class A analog output stage.

With such unit you are set for life, have the best redbook performance, and ability to bring high resolution signals (88.2, 96, 176.4, 192 kHz) what is in the near time future for material distribution, with superb jitter immunity.
Price it at near 10K, and kill dCS, Weiss , EMM, and likes, the “reference” DAC manufacturers.
When will you release the product, I am buying? 

[FM Acoustics]

...we wanted to optimize the digital quality by Clocking the Drive to the DAC to eliminate Jitter. Having a Digital input would mean that we would have to have another circuit to reclock and resample the incoming signal from the external drive etc.

James, this is exactly what I proposed you do for the the BDA-1 DAC with the Word Clock output, this way you can slave the transport to the BDA-1 clock. Right now the BDA-1 works only like you say about the needed circuit for a BCD-1 with a digital input: it re-clocks and re-samples the input signal.

[KeithA]

The advantage of the CD Player of course is that the DAC and the Drive can be clocked through a Master clock and that eliminates any jitter issues. Our intention is to have a second cable -clock cable- from our External Drive that will clock back to the BDA-1 and therefore allow for the same synchronization of DAC and Drive as in our CD Player.

I haven't been paying much attention to this, but I thought that based on James' post above that the BDA-1 will incorporate this concept so that it somehow works this way with the new Drive in development. Did I miss something or has this concept been tossed out?

Keith

[James Tanner]

Hi,

Yes the new Bryston Drive (BD-1) will be designed to clock to the BDA-1. As far as I know you have to KNOW the clocking frequency before you can slave and therefore there is no such thing as a universal master clocking mechanism?

james

[FM Acoustics]

Hi,

Yes the new Bryston Drive (BD-1) will be designed to clock to the BDA-1. As far as I know you have to KNOW the clocking frequency before you can slave and therefore there is no such thing as a universal clocking mechanism?

james

James, what do you mean with you have to know the clocking frequencies? Does it mean an oscillator (especially a high quality one that is very stable) can't be made to output all the sampling frequencies, so when you select an oscillator you also select the frequencies it can provide? I was just reading the Sync section from the Prism Orpheus multichannel AD/DA manual and I don't know if this is how they design their stuff but one solution may be to use one specific oscillator for every sampling frequency (44.1 to 192 kHz), a bank of oscillators like they say:

The externally-clocked design challenge has traditionally been a trade-off. since the more stable a
clock oscillator is, the less is its range of frequency adjustment: but we would ideally like an oscillator
which can operate over a wide range of sample rates, perhaps from <44.1kHz to >48kHz, plus
multiples thereof. But such an oscillator would inevitably have poor stability – at least in terms of the
stringent requirements for high-quality audio conversion. On the other hand, if we limit the range of
rates at which the oscillator needs to operate to small ‘islands’ around the standard sample rates we
could use a bank of oscillators, selecting the appropriate oscillator according to our desired sample
rate. But this is expensive and, in any case, the 'pull-range' of an ordinary quartz crystal oscillator is
still generally insufficient to meet the tolerance demands of the digital audio interfacing standards

As well as outputting a clock at the selected sample rate, Orpheus' wordclock output can be
configured to produce a '256x clock' (a clock at 256x the selected sample rate, e.g. a 'superclock') or
a 'base clock' (44.1kHz if the sample rate is a 44.1kHz multiple, or 48kHz if the sample rate is a
48kHz multiple).

http://www.prismsound.com/m_r_downloads/Orpheus_Operation_Manual_LTR.pdf

Esoteric DACs also can output all the sampling frequencies up to 192 kHz through their Word Clock output but I don't know how they do it.

In the Pro AD/DA units you can usually find Word Clock outs which support all the sampling rates, check the Lynx Aurora, Crane Song Heed 192, Universal Audio 2192 etc. You should also check the Gearslutz forum ( www.gearslutz.com ), lots of pros there who can give input. This would be the time to use the Bryston pro connections and see what are the implementations of this feature ...

[James Tanner]

Hi FM,

Good info thanks - my understanding is the Word Clock is a poor cousin of the Master Clock so a master clock is the most accurate way to clock. I will run this by our digitalguys and see if I can get a more detailed answer.

james

[James Tanner]

Hi FM,

Good info thanks - my understanding is the Word Clock is a poor cousin of the Master Clock so a master clock is the most accurate way to clock. I will run this by our digitalguys and see if I can get a more detailed answer.

james

Engineering tells me you would need independent oscillators (clocks) per frequency.

james

[FM Acoustics]

Engineering tells me you would need independent oscillators (clocks) per frequency.

james

If this is the only way to provide Word Clock outputs for all the 5 standard sampling frequencies does it mean that all the DACs with WC outs have 5 oscillators in them and every time you select a different sampling frequency you activate a different oscillator?

Then the Word Clock generators like the ones from Antelope should also work this way...

http://www.antelopeaudio.com/en/products_iso.html
http://www.youtube.com/watch?v=48CIWloLyTU

[alexone]

 impressing inputs, FM!

 


 alex.

[FM Acoustics]

 impressing inputs, FM!

 


 alex.

Thanks Alex!

[James Tanner]

Thanks FM - I will have our guys look this over.

james

[vegasdave]

Will the bda-1 work as well with other makes of cd transports?

[James Tanner]

Will the bda-1 work as well with other makes of cd transports?

Hi Dave,

Yes the BDA-1 will work very well but you have to resample and reclock the incoming digital signal.

james

[FM Acoustics]

James, take a look at this RME pro audio interface; when set to master it can output all the sample rates and it has only one oscillator. Maybe the oscillator provides only the base sample rate and then it uses some 2x and 4x clock multipliers. It's true that the specified jitter is <1ns so high jitter must be the trade off for this solution.

http://www.cirrus.com/en/products/pro/techs/T16.html

[vegasdave]

Will the bda-1 work as well with other makes of cd transports?

Hi Dave,

Yes the BDA-1 will work very well but you have to resample and reclock the incoming digital signal.

james

I see. Thanks again.

[James Tanner]

James, take a look at this RME pro audio interface; when set to master it can output all the sample rates and it has only one oscillator. Maybe the oscillator provides only the base sample rate and then it uses some 2x and 4x clock multipliers. It's true that the specified jitter is <1ns so high jitter must be the trade off for this solution.

http://www.cirrus.com/en/products/pro/techs/T16.html

Hi FM,


Yes the very high Jitter figure with one oscillator seems to support our research as well. Our CD Player and the new External DAC have jitter figures that are difficult to measure even with the best test gear available.  Picoseconds rather than Nanoseconds - a factor of 1000 times better jitter rates.

Some have suggested that Word Clocks are convenient for clocking a variety of different digital products together but not if ultimate performance is the goal?

james
 

[FM Acoustics]

Some have suggested that Word Clocks are convenient for clocking a variety of different digital products together but not if ultimate performance is the goal?

james

Hi James,

Word Clock slaving is very good for ultimate performance but if you do it right. Word Clock generators like the ones from Antelope are mostly used in the studios where there are many digital devices which have to work on the same clock. Esoteric and dCS also sell standalone clocks. You are right in saying that these machines can't give very good results. I wasn't advocating the use of a standalone Word Clock to which you will slave both the DAC and the Transport. The point of Word Clock slaving of the Transport to the DAC is making the DAC work only from its internal Clock thus not having to extract the clock from the incoming AES or SPDIF signal through a PLL. Using an external Master Clock won't let the DAC work on its internal Clock, the DAC will receive the clock through another cable and will not have to extract it from the AES/SPDIF signal, but would still be worse than working on its internal clock to which the Transport will be slaved.

On the thread I opened concerning the BDA-1 my last post refers to another thread on the Slim Devices forum with the subject being the slaving of the Transporter to a DAC with WC out (dCS Scarlatti). Here are a few responses from the SD founder who argues with a guy about the necessity of using an external Master Clock unit to which to slave both the DAC and the Transporter contrary to slaving the Transporter directly to the DAC:

Quote:
Yes it is a manual setting. Please, notice that I use a DAC and en external clock, i.e. two units.

?!? Why?

Such a configuration should only be used if you have some requirement to synchronize multiple _source_ components, perhaps for editing purposes.

It is the MCLK (eg 11.2896MHZ) signal that actually drives the internal operation of a modern DAC chip, and the whole point of word clocking (for the purpose of reducing jitter) is to put that clock as close as possible to the DAC chip itself.

A PLL is absolutely _terrible_ at generating a master clock from a word clock, compared to generating it directly with a crystal. But that is not even the only source of jitter - you are also accumulating it in all the connections between this equipment, and in the clock source device itself, as it has to divide a crystal-generated clock internally to produce that low word clock frequency.

I am not aware of any situation where a word clock would be advisable for driving a DAC. You will get jitter much worse than anything you'd get even from traditional s/pdif master->slave clocking.... i.e. this is not only defeating the jitter eliminating mechanism of the word clock interface, but is actually making the jitter far worse even than plain s/pdif. You are probably running your DAC on a few hundred picoseconds of jitter, as opposed to the 30ps or less that would come from a good quality internal oscillator.


Quote:
2) Even better is to syncronize both the DAC and the Transporter to an external clock - if this clock is of higher precision than the one in the DAC.

No, this is where you are very wrong. I have already explained why from a theoretical standpoint, but to put it another way, which do you expect will have more jitter:

- A crystal oscillator running at 12.2880 MH, directly driving the DAC

Or

- A crystal oscillator running at 12.2880 MHz
- driving either a synchronous counter or a series of flip-flops, to divide that signal down to 48 KHz
- then feeding this signal through some transmission circuit to a BNC connector
- coupling that signal into a cable
- feeding it down the cable
- getting it into another connector at the other end of that cable
- driving that signal into a PLL circuit which multiplies the word clock signal back up to 12.2880 Mhz
- feeding the output of that PLL into the DAC chip.


Quote:
Finally, I still can not understand your theory of internal vs external clock (high precision oscillator) for a DAC. Please, notice that both Esoteric and dCS promotes this idea - and for me it works well with the Transporter and 44.1kHz.

Which part of it is unclear?

Consider an absolutely perfect clock with zero jitter. No such thing exists, but let's just suppose for the sake of argument that your external clock source is such a device.

Now, divide that clock signal down to word clock speed (/128 or /256), send it through a bunch of cables and connectors, through a PLL to multiply it back up to MCLK speed, and then across another circuit board to the DAC chip. How can that possibly still be a clean clock? How could it possibly be cleaner than if you placed the crystal oscillator right next to the DAC chip? It can not. Not by any stretch of the imagination, and not even if you consider a _perfect_ external clock source compared to the poorest imaginable local crystal clock source. It is not even close. The external clocking scheme is worse by about a factor of ten. In practice you would get about 15-50ps for the internal clock, versus 100-300ps for the external, PLL-recovered clock.

The fundamental principle of word clocking, when used for the purpose of reducing jitter, is that you are eliminating all the crap between the clock source and the DAC. This is where jitter comes from. The quality of the crystal oscillator is actually not even a major factor.

Finally ask yourself, if dCS can produce a better clock signal through such a convoluted means, why would they not then simply build this technology into their $18K(?) DAC? Maybe they just want to sell you yet another overpriced box.

Look, I am not making this up and I have nothing more to sell you. What I am telling you is all solid theory that can easily be tested with suitable equipment.

http://forums.slimdevices.com/showthread.php?t=39770&highlight=word+clock

[James Tanner]

Thanks FM

I know in our CD Player and our External DAC that our engineer placed the DAC and the Oscillator as close to each other as physically possible.

james