USB unlimited

Vincent Kars said:

Lot’s of people think that USB is limited to 16 bits / 48 kHz sample rate.
Small wonder, there are many USB DACs incapable doing anything > 48.

USB class audio 1 is tied to the USB 1 spec.
USB doesn’t specify a maximum sample rate or a number of channels.
You simply tell the bus what the properties of the audio stream are.

Full speed USB allows for 1 package of maximum 1024 bytes pay load each millisecond.
This is about 7.8 Mbit/s
A 2 channel 24 bit 96000 Hz recording = 4.4 Mbit/s so it fits in.
The next common sample rate 172 kHz requires 8.07, just a bit too much.

The other way round: 24*2*176400= 8467200 bit/s or 1058.4 Byte/ms
Too much given the package limit of 1024.
Obvious the USB 1 Full Speed bus limits the resolution.

Now USB 2 High Speed is 40 times faster than Full Speed.
Obvious this bus is not the limiting factor anymore.

This explains why USB 2 DACs like Antelope’s Zodiac do 32 bits at 384 kHz over USB 2.
Both OSX and Linux supports this as part of the USB audio class 2.
Win doesn’t have a class 2 driver

Obvious with high speed USB DACs the limit in resolution is only of theoretical value

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Light Harmonic said:

Yes. Right now, our Da Vinci DAC also support 384K/32Bit over USB 2.0
In our Titan USB module, we already successfully output 10 channels of 192K/32Bit or 4 channels of 384K/32Bit... So for USB 2.0 Audio Class 2.0 standard, the speed limitation is really NOT a problem for now.

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