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RE: John Swenson on Sata cables

Posted by Tony Lauck (A) on July 10, 2014 at 08:30:16

In Reply to: RE: John Swenson on Sata cables posted by Ugly on July 10, 2014 at 07:35:54:

I don't see how reducing noise a little in the computer system is going to reduce the error rate (bit error rate) on a USB cable, unless junk equipment or cables are used or excessively long cabling is employed. The bit error rate on USB is going to be zero, for all practical purposes. If you look at the USB specifications you will see what the noise margins are for this system.

The problem with computer audio is noise being transferred from the electrically noisy computer to the critical analog components of the playback chain, starting with the master clock that controls the timing of digital to analog conversion and working downstream from there toward the speakers. The resulting sound quality will depend on the amount of noise generated multiplied by the fraction transferred to the analog equipment multiplied by the sensitivity of the analog equipment.

Most of the USB errors that people get are timing errors, because USB audio is streamed in real time. These can be minimized by reducing competition for computing resources (latency) or by increasing buffer sizes. This is easily seen with my Mytek DAC and the USBPAL control panel. The error rates can be made quite large by setting the buffer size to the smallest possible and then loading up the computer with lots of non-audio tasks or having my player software do extensive DSP. They are zero when the computer is configured with somewhat larger buffers, providing that it is dedicated to audio.

Unfortunately, setting large buffer sizes is not a panacea. While it may eliminate USB timing errors the pattern of noise generated by the computer system changes. Since some fraction of this noise gets coupled into the analog circuitry this has an effect on sound quality. Generally, the smaller the buffer sizes the less the audible effect, at least that's been most people's experience, including mine. So I run with the smallest possible buffer sizes so as not to get errors, or at least not to get audible errors. (The audibility of buffer errors depends on the music being played and also the size of the buffers being dropped. With large buffers almost every drop is audible unless the music is silent. With small buffers, some fraction of buffer drops will not be audible unless the listener is very attentive.)

With my system, reducing the buffer sizes makes a small improvement in sound quality, similar in magnitude to raising or lowering the window blinds behind my speakers or moving my display forward or back a few inches. It is not "game changing" but it's definitely noticeable. I would be surprised if SATA cables would change sound quality for my system, because most of the time that I am listening to music there is no disk I/O going on because I play audio files off a RAM disk. (My music library is mostly stored in FLAC on a hard drive and I convert an album to WAV and load it into the RAM disk prior to listening. This provides improved sound quality while still saving space on disk.)








Tony Lauck

"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar

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