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Old 15th April 2013, 01:09 PM   #21
rsowen is offline rsowen  United Kingdom
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I've worked with DACs from most (if not all) manufacturers, both directly and indirectly via customers. I have also had contact with DAC designers , but I cannot really discuss this I'm afraid (We have quite a few silicon and hardware designers in house also )

Edit: I see that you quite significantly modified your last post, I don't have time to re-reply now.

Last edited by rsowen; 15th April 2013 at 01:27 PM. Reason: Update to previous post.
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Old 15th April 2013, 01:58 PM   #22
rsowen is offline rsowen  United Kingdom
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Btw its is important to realise we are coming from two separate angles, mine being building complete systems/products from scratch. Yours (I think) being adding external modules to existing DAC products.
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Old 15th April 2013, 05:13 PM   #23
glt is offline glt  United States
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Quote:
Originally Posted by Nanoloop View Post
Here jitter is measured on old xmos and crystal on evm.

mclk is good but other bclk, etc not good.

XMOS USB Audio 2.0 Reference Design Jitter Measurement

and here say xmos is best.

USB DAC 2 - Hi-Resolution System
Yes, that is probably the most detailed measurement on the "old" chip.
Yet many high end products have used this chip in their USB input implementation.
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Old 16th April 2013, 01:06 AM   #24
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Maybe they choose it because it can do 384khz.
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Old 16th April 2013, 01:21 AM   #25
qusp is offline qusp  Australia
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yes, I prefer to modify or add to one post, rather than making multiple posts, it happened long before you replied. maybe read the post instead of the notification email... your assumption would have been right a year or 2 ago. well not modifying in the way you mean it. i'm using someone elses design at the moment for buffering though that puts out ~1ps at the clock buffer for all of the signals and drives a dual mono ESS synchronously with dual clocks, so.... but most is built from blank PCBs along with a few bits and pieces of my own, only recently have I started on an integrated design of my own though, I admit.

I dont see how having a complete systems approach negates anything I said actually, just reads like an opportunity to beat your chest.

obviously, as I said, you would just do something about it with a clock buffer or logic/flip flops if you were doing a PCB of your own and its even more important to keep in mind that WE ARE TALKING ABOUT A MODULE, 2 modules even, not an integrated device; dont move the goal posts so as to more easily score...

I sure wouldnt leave that amount of jitter on there for the dac to clean up and if you would, regardless of the dac chip, then I will happily let you keep your trade secrets.

perhaps you are XMOS? ive seen them defending this very issue before

Last edited by qusp; 16th April 2013 at 01:41 AM.
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Old 16th April 2013, 01:22 AM   #26
qusp is offline qusp  Australia
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Quote:
Originally Posted by Nanoloop View Post
Maybe they choose it because it can do 384khz.
this and the 'driverless' operation, plus multichannel. its an interesting range of parts, but using them bare, without reclocking at least the last ones, is dubious

to be clear, I would love if they had fixed the issue, the development environment looks very good and they have made a flexible, reasonably powerful set of parts that would require FPGA coding and maybe some glue logic to achieve otherwise. its completely solvable with adding a reclocking stage, sure, but it would be nice if it wasnt that bad to begin with. saying it (the BCK signal) doesnt matter, as is however, is another thing entirely

Last edited by qusp; 16th April 2013 at 01:38 AM.
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Old 16th April 2013, 01:58 AM   #27
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Quote:
Originally Posted by qusp View Post
perhaps you are XMOS? ive seen them defending this very issue before
His affiliation is stated openly on his profile :

Occupation Senior Development Engineer, XMOS Semiconductor Ltd
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Old 16th April 2013, 09:27 AM   #28
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Mr Owen,

I am very interested to know what improvement new xmos is. Have you done tests on old vs new ? Can you say or is it secret ? What is technical performance benefit of faster USB analogue node clock ? What Mhz speed is best ? Does integrated USB give performance benefit or is it for convenient/cost reasons ?

Thank you.
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Old 16th April 2013, 09:47 AM   #29
rsowen is offline rsowen  United Kingdom
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Regarding the TDA1541A previously mentioned, please re-read what I wrote.
Quote:
Originally Posted by rsowen
A DAC would not use the BCLK when MCLK is available. If you are using a DAC that does not take an MCLK but internally generates based on LR on BCLK (via a PLL or similar) then perhaps this is an issue, but the product is probably "low-end" anyway.
The TSA1541A does not have separate MCLK and BCLK inputs. In the case of the TAD1541A the bit clock used for audio rendering with no PLL involved, it is the master clock if you like, and therefore should be treated as such. If I was asked to design with this DAC IC (highly unlikely I suppose now...) the clocking methodology would of course allow for this, but this would be a special case. Sometimes these do happen - a recent implementation involving DSD support on a fairly old TI/Burr Brown DAC design did require some thought.

I believe the design of a all-things-to-all-men (or woman, there are a few out there!) module intended to be used with an external DAC product is very different to the design of a constrained system (I am normally involved in the latter). The previous statements seemed to be directed at XMOS implementations in general. That module does have an MCLK out which you are free to use however you see fit.

By the way, I do know know of the module provider, its performance or otherwise, but good luck to the chap

Quote:
Originally Posted by Nanoloop
Maybe they choose it because it can do 384khz.
I don't believe so, I would say over 95 percent of designs I have been involved with don't use 384kHz. In fact a lot of designs actually restrict the rate of their products to 96kHz...

Quote:
Originally Posted by qusp View Post
this and the 'driverless' operation, plus multichannel.
"Driverless" operation is based on full-speed Audio Class 1.0 operation to remain spec compliant so has its restrictions I'm afraid (stereo up to 96kHz for input OR output, 48kHz for input AND output). Multi-channel is obviously a big area for XMOS, especially recording.

Quote:
Originally Posted by abraxalito
His affiliation is stated openly on his profile :

Occupation Senior Development Engineer, XMOS Semiconductor Ltd
Yes that is my day job, however, I signed up here in a personal capacity - but it is best to be open about who are I believe.

If I can help people with any projects then fantastic I didn't really wish to be involved with discussions about clocking, but there seemed to be some confusion regarding the statement in the advert regarding the 48MHz oscillator on this thread, hence my involvement. It is often best to support people in the open, since everyone can benefit (and my email inbox is not as strained!). Im not really interested in "chest-beating" or "scores" I'm afraid.
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Old 16th April 2013, 09:52 AM   #30
rsowen is offline rsowen  United Kingdom
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Quote:
Originally Posted by Nanoloop View Post
Mr Owen,

I am very interested to know what improvement new xmos is. Have you done tests on old vs new ? Can you say or is it secret ? What is technical performance benefit of faster USB analogue node clock ? What Mhz speed is best ? Does integrated USB give performance benefit or is it for convenient/cost reasons ?

Thank you.
The main benefits are integration of the USB phy and power-supplys (from a Bill of Materials point of view). The clock speed shouldn't make any difference, performance should be the same.

Cheers
Ross
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