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Old 4th July 2018, 07:13 AM   #11
Max Headroom is offline Max Headroom  Australia
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IME different 'off the shelf' USB cables most certainly can alter system sound, subtly but evident nevertheless.
'Theoretically', fitting a ferrite filter around USB cable should cause zero change in system sound, in practice I find this is not true.
Fitting a non magnetic filter (propriety) around USB cable should cause zero change in system sound, in practice I also find this is not true.

Dan.
 
Old 4th July 2018, 07:29 AM   #12
JPS64 is offline JPS64  Germany
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Im using USB for military custom development.
Ive used COTS cable at the beginning with very bad results although cable marking High Speed USB (cheap or expensive ones, dont care).

After a lot of expertising with a lot of measurements (LeCroy with fixture according USB standard, eye diagram...) we state that this is like russian roulette.
So we decide to use only custom made and qualified cable from Draka.
We dont need any ferrite on cable, but the interface is ESD protected and CMC EMI filtered on PCB.
This is a technical issue.

My 2 cents.
JP
 
Old 4th July 2018, 07:47 AM   #13
Pygmy is offline Pygmy  Netherlands
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Quote:
Originally Posted by Max Headroom View Post
IME different 'off the shelf' USB cables most certainly can alter system sound, subtly but evident nevertheless.
'Theoretically', fitting a ferrite filter around USB cable should cause zero change in system sound, in practice I find this is not true.
Fitting a non magnetic filter (propriety) around USB cable should cause zero change in system sound, in practice I also find this is not true.

Dan.


If there is a difference then the USB cable - which transmits a digital signal - is broken, because it's not transferring the correct bits.

Either it transfers all bits correctly, or it doesn't thus it's broken.
It's really not polishing up the ones while they're being transferred.

Even if you think it must be jitter, no really, it doesn't matter.
Archimago's Musings: MEASUREMENTS: USB Cables for Audio DACs. [2013-06-18 UPDATE]
 
Old 4th July 2018, 08:43 AM   #14
lcsaszar is offline lcsaszar  Hungary
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USB is an asynchronous transmitting method, where clock is retrived from the data stream by using a PLL at the receiving end. The data stream can be characterized by an eye pattern, similar to the CD transport. The USB cable clearly affects the shape of the signal at the receive end, there are methods for physical layer measurements, like this:

Understanding and Performing USB 2.0 Physical Layer Testing

The USB cable affects signal shape, that has influence on jitter. In digital domain, jitter is bad for audio No wonder there is difference between sonic characteristics of USB cables (and Toslink, and SPDIF and all similar async digital audio tranfer).
 
Old 4th July 2018, 09:02 AM   #15
Max Headroom is offline Max Headroom  Australia
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Quote:
Originally Posted by JPS64 View Post
Im using USB for military custom development.
Ive used COTS cable at the beginning with very bad results although cable marking High Speed USB (cheap or expensive ones, dont care).
After a lot of expertising with a lot of measurements (LeCroy with fixture according USB standard, eye diagram...) we state that this is like russian roulette.
Like I said.

Quote:
So we decide to use only custom made and qualified cable from Draka.
We dont need any ferrite on cable, but the interface is ESD protected and CMC EMI filtered on PCB.
This is a technical issue.
Thanks JP.
Can you give details of the Draka cable type that you are now using ?.

Dan.
 
Old 4th July 2018, 09:04 AM   #16
Max Headroom is offline Max Headroom  Australia
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Thanks.


Quote:
The USB cable affects signal shape, that has influence on jitter. In digital domain, jitter is bad for audio No wonder there is difference between sonic characteristics of USB cables (and Toslink, and SPDIF and all similar async digital audio tranfer).
Yes.


Dan.
 
Old 4th July 2018, 09:45 AM   #17
JPS64 is offline JPS64  Germany
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Dan,


Im not at business today. Ill give you answer tomorrow.


JP
 
Old 4th July 2018, 10:15 AM   #18
Max Headroom is offline Max Headroom  Australia
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.
 
Old 4th July 2018, 10:45 AM   #19
00940 is offline 00940  Belgium
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Quote:
Originally Posted by lcsaszar View Post
USB is an asynchronous transmitting method, where clock is retrived from the data stream by using a PLL at the receiving end. The data stream can be characterized by an eye pattern, similar to the CD transport. The USB cable clearly affects the shape of the signal at the receive end, there are methods for physical layer measurements, like this:

Understanding and Performing USB 2.0 Physical Layer Testing

The USB cable affects signal shape, that has influence on jitter. In digital domain, jitter is bad for audio No wonder there is difference between sonic characteristics of USB cables (and Toslink, and SPDIF and all similar async digital audio tranfer).
I think you're confusing adaptive and asynchronous protocols. What you describe is true for adaptive endpoints (the pcm2*** serie from TI for example). Definitely not for the more modern interfaces like xmos, which work as asynchronous endpoints.

There are 3 modes for audio transfer under USB audio. All 3 are falling in the isochronous category (real time with no error correction).

From the USB Device Class Definition for Audio Devices:

Quote:
3.3 Audio Synchronization Types

Each isochronous audio endpoint used in an AudioStreaming interface belongs to a synchronization type as defined in Section 5 of the USB Specification. The following sections briefly describe the possible synchronization types.

3.3.1 Asynchronous
Asynchronous isochronous audio endpoints produce or consume data at a rate that is locked either to a clock external to the USB or to a free-running internal clock. These endpoints cannot be synchronized to a start of frame (SOF) or to any other clock in the USB domain.

3.3.2 Synchronous
The clock system of synchronous isochronous audio endpoints can be controlled externally through SOF synchronization. Such an endpoint must do one of the following:
• Slave its sample clock to the 1ms SOF tick.
• Control the rate of USB SOF generation so that its data rate becomes automatically locked to SOF.

3.3.3 Adaptive
Adaptive isochronous audio endpoints are able to source or sink data at any rate within their operating range. This implies that these endpoints must run an internal process that allows them to match their natural data rate to the data rate that is imposed at their interface
For more details on the synchronization methods, see section "5.10.4.1
Synchronization Type" from the Universal Serial Bus Specification Revision 1.1.
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Old 4th July 2018, 10:59 AM   #20
nigelwright7557 is offline nigelwright7557  United Kingdom
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Copper quality could make a difference to the signal. A piece of wire isn't just a piece of wire, the resistance varies a lot between different wires.

Also excessive length of cable will make a difference.
You should be using the shortest length of cable as possible.

The number of items on the same bus will affect data quality too as each loads the bus a little more.
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