USB cable hype

Kijanki, Your point about checksums is interesting. Let's say that a packet is dropped. What would take the place of the dropped packet? Would it be that the contents of previous packet are duplicated? Dropped packets are problematic regarless of how they are manged. The only good solution is o resend the packet.

With a buffer large enough for several minutes of audio, there would be ample time to resend packets. Does USB audio comply fully to USB standard specifications? The answer to that question would go a long way. Thanks.

Zd542, I have seen dual headed USB cables with one connector dedicated to power and the other to signal. But I am not sure about which thread you mean. I searched "Dual Headed USB hookup" in Audiodon and nothing came up.

Axle, I'm assuming, that without resending it would be 1ms gap. Not bad if it happens once but can sound pretty bad if frames are dropped often. I found some info and interesting computer audio FAQ site:
http://www.thewelltemperedcomputer.com/KB/USB.html

Kijanki, If USB DACs use off-the-shelf USB chipsets (why not?), then they can detect errors and negotiate re-transmission. The bits should be error-free.

Thanks for the link. I like it.

There are four transfer modes: control, interrupt, bulk, and isochronous. It seems that bulk transfer (as long as the buffer is large) is the way to go.

“Interrupt and bulk data transfers conclude with a handshake packet to provide confirmation that the data was received, or request that it be re-sent if it was not. Delivery of this data is therefore guaranteed, even if the time taken to deliver it is not.”

But there is no guaranteed access to the bus in bulk trasfer mode. If you want guaranteed access to the bus, then you must use isochronous mod.

"With isochronous data it is not possible to retry a failed transaction. Since only one ‘slot’ is allocated to the pipe during each frame, resending the data would delay transmission of the succeeding data samples, upsetting the time element of the data delivery. Consequently no handshake packet is sent and the data must be accepted ‘as is.’”

Bulk mode can be used for a dedicated music server because the bus is free. But isochronous mode is required for computers. Question is, do you have a choice? If not, you have to accept the default mode of the DAC, which is likely isochronous.

The answer to the question “are bit errors recovered?” and therefore "do cables matter?" is “it depends on the transfer mode”.