PRR said:
> Can you actually squeeze 24 channels of digital audio down a USB port??
I too remember choking early USB with CD-rate audio.
Original-flavor USB would barely cover a CD. Stereo 16-bit 48K. 1.5 Mbit/s and 12 Mbit/s
USB 2.0, which is 14 years old, is 480 Mbit/s (effective throughput is limited to 280 Mbit/s). 23.3 times better, so it works for 24 channel 16 bit 48K.
USB 3.0, 6 years old but not so widely adopted as 2 was, claims usable data rate of 500 MB/s.
We like better-than-CD quality in production. Say 24 bit 96K (2,304 Kbits/S), times 24 channels, is ~~56,000 Kbits/S or 56Mbits/S. Far short of USB3's capacity, about 20% of USB2's capacity.
Arithmetic corrections welcome.
Not an arithmetic correction, but rather one of specification. Saying that a device complies with USB 2.0 does not at all indicate its transfer rate.
A device which adheres to the USB 1.1 spec may run at the Low Speed (1.5 Mbps) or the Full Speed (12 Mbps).
A device which adheres to the USB 2.0 spec may run at the Low Speed, the Full Speed, or the High Speed (480 Mbps).
A device which adheres to the USB 3.0 (or 3.1, whatever they're up to now) can run at those three speeds, or at the new Super Speed (5 Gbps for USB 3.0, 10 Gbps for 3.1).
There are a lot of USB devices which are 2.0 compliant yet run at Full Speed. This is perfectly OK, and from the user's point of view, it doesn't really matter. (OK, perhaps it does if the device is a disk or flash drive, in which case the user will hate Full Speed.)
One more caveat. The above is about the overall USB specification. That is separate from the various Device Class specifications, among them HID (Human Interface Device, which is your keyboard and mouse and game controller, but can be used for custom devices, too), CDC (communications device class, which is your USB-to-RS232 adapter and other such things), the Printer class, the Mass Storage class, and of course the Audio Device class (which also includes MIDI).
The boner is that to take advantage of High Speed for audio devices you must use the Audio Device 2.0 spec. The Audio Device 1.0 spec, written before such a thing as High Speed existed, doesn't work with High Speed for various technical reasons. Apple has supported the Audio Device Class 2.0 with a driver since OS X 10.5, which was ages ago. To this day, Windows does not support Audio Device Class 2.0, and as such any manufacturer who wants their multichannel USB audio product to work in Windows has to either write or farm out for a driver. Go figure.
