Anyone read that article?
Marlene's Musings: Vodoo continued: my final Statement on USB cables
It's the last one from a series with final conclusion.
He eared differences, he tried to measure, he found differences in measurements but later discovered that his measurements where faulty.
After fixing his mesurements he found no differences at measurements but still recognize differences with ABX via Foobar (!)
Interesting... it seem we need better measurements, after all.
I find it hard to believe someone who understands so little about digital audio formats and there transmission. This is obvious from the posting of analog measurements that are 10 db different for specs that can not be changed in the digital format (without massive bit errors ) like dynamic range (does one cable lose the LSBit) or crosstalk. It took a year for him to figure this out? Maybe next year he will figure out that his ABX testing was also faulty. Where are the jitter tests? One of the few things that actually make a difference in real time dig audio transmission (not buffered).
Do I understand very little about digital audio formats and their transmission? I find it very interesting that you seem to know this. A groundloop (which was the cause for different measurements) has nothing to do with digital systems.
For all the people who were asking: USB_Comparisons.rar
These are the files derived with different USB cables. BTW, the link already was in the first article
Before I forget... my test conditions / setup were described in detail (text form) in the first and the third article. I´m not going to re-state them here.
All you girls/guys make these articles much more important than they really are. I´m neither a scientist nor an engineer, I make this clear in many of my posts. C'mon, I measure using RMAA. The measurements I posted are nothing more than nice pictures. It doesn´t matter that I repeated them five times for each cable.
However, I continue to hear the effects of different cables. Since a PC and a soundcard are a closed and controlled system behaving to certain pre-set rules and conditions, there MUST be measurable differences as well. My three USB articles were however only able to tell me one thing: the measurements I did were obviously insufficient.
All you girls/guys make these articles much more important than they really are. I´m neither a scientist nor an engineer, I make this clear in many of my posts. C'mon, I measure using RMAA. The measurements I posted are nothing more than nice pictures. It doesn´t matter that I repeated them five times for each cable.
However, I continue to hear the effects of different cables. Since a PC and a soundcard are a closed and controlled system behaving to certain pre-set rules and conditions, there MUST be measurable differences as well. My three USB articles were however only able to tell me one thing: the measurements I did were obviously insufficient.
Hi Clave,
I did try and edit my response but my internet is playing up.
The measurement tools we have these days are very good and have the ability to measure what we can hear to a higher resolution than we can hear.
With a digital interface the only way to determine differences is to measure the digital signal transmission (network analyser, even a scope will show the general shape of the wave) and to check it is getting there correctly. If noise is suspected, again you can measure this and solve it with filters or different power supplies.
If someone hears a difference but cannot measure it then IMO:
There measurement techniques need improving. or
There is no difference.
Not the most popular opinion, but to assess a digital transmission set up with audio you cannot use listening alone, you have to measure the transmission system, check that any software and/or firmware is operating properly as well as assess the quality of the audio with subjective listening.
Glad to help with the PCB design
I did try and edit my response but my internet is playing up.
The measurement tools we have these days are very good and have the ability to measure what we can hear to a higher resolution than we can hear.
With a digital interface the only way to determine differences is to measure the digital signal transmission (network analyser, even a scope will show the general shape of the wave) and to check it is getting there correctly. If noise is suspected, again you can measure this and solve it with filters or different power supplies.
If someone hears a difference but cannot measure it then IMO:
There measurement techniques need improving. or
There is no difference.
Not the most popular opinion, but to assess a digital transmission set up with audio you cannot use listening alone, you have to measure the transmission system, check that any software and/or firmware is operating properly as well as assess the quality of the audio with subjective listening.
Glad to help with the PCB design
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Hi Marce,
I was refererring to measurements made by Marlene.
Absolutely
Absolutely, if you want to be absolutely certain and not victim of some sort of placebo effect.
Sadly the required equipment and/or knowledge it's not at everyone disposal and sometimes we have to rely on our ears and brains with all the associated limits.
BTW
To me it seem a particular factor in digital trasmission in audio is often overlooked in these debates.
Streamed data is not necessarily bit perfect, it don't need to be (a missing chunk of data can be interpolated with acceptable loss) , much more critical is its timing.
One of USB's tranfer modes is isochronous transfer, used for audio and other time critical transmissions.
Such mode has no error detection or recovery so the quality of the cable (in terms of signal integrity it offers) is critical.
The file transfer or 'Notepad' examples are not relevant since the transfer mode used in such cases is bit perfect (in case of error data is retransmitted) and a worse quality cable simply affect speed and not data.
Glad to help with the PCB design
Results are really interesting, the amp sound really good and measures by some of the partecipants are also very good.
This thread has amused me, its similar to HDMI cable discussions i've read
but it does get me thinking
say our cheap cable is more prone to interference, it is therefore possible in severe cases, for our 0's and 1's to become vague? but would'nt the USB interfaces pass parity information which would make the sender/receiver aware of a corrupt word, and resend the word?
So in theory the resending of the word would put an incredibly small delay into the transmission... so how woudl the recipient (DAC) deal with this delay? does it buffer to compensate fora few dropped words or bits? and therefore it would be un noticable after the DAC has worked its magic?
but it does get me thinking
say our cheap cable is more prone to interference, it is therefore possible in severe cases, for our 0's and 1's to become vague? but would'nt the USB interfaces pass parity information which would make the sender/receiver aware of a corrupt word, and resend the word?
So in theory the resending of the word would put an incredibly small delay into the transmission... so how woudl the recipient (DAC) deal with this delay? does it buffer to compensate fora few dropped words or bits? and therefore it would be un noticable after the DAC has worked its magic?
From the link I've posted:
The USB protocol provides no error detection or recovery for Isochronous transfers. If no data is transferred or the data is corrupted, no error information is passed to the application. No retries are performed and subsequent packets of a partially failed transaction are nevertheless transferred.
No buffering is provided. If an application does not listen on an IN Isochronous endpoint, the produced data is lost. If an application must be sure to capture all isochronous data, it will have to work with at least 2 input buffers to ensure that data continues to be captured when the first buffer is full.
Even if the bits become vague they will still be read as either a 0 or 1, though bits may be dropped. This would be noticeable, not as increased noise but as drop outs. If the shielding was not up to the job you would get noise, but in either case the cable is not up to the job and should be binned.
A well engineered cable should avoid these problems, without having to resort to audiophile over priced USB cables.
I am not sure why you would be amused...
I can't see why any cable effect would be limited to 1's and 0's. If, as you surmise, the cable is prone to interference, why would this not affect a non galvanically isolated DAC? The grounds will be polluted with the "interference".
I know you aren't thick, so why limit your answers to simple first order effects, what is your purpose other than to be argumentative? If this were all there is to it there would be no need for Asynchronous protocols and galvanic isolation. Why do you suppose those were implemented? Why bother shielding USB cables either?
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Why do you think this is the only way audio is transfered over USB.
USB audio - Synchronous/Asynchronous
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