Improved USB interlink for digital audio

Improved USB interlink for digital audio

USB was developed to connect peripherals like printers, scanners, mice, keyboards and storage devices to a PC, not for streaming digital audio. Incorrect received data can be re-sent as many times as required to ensure correct data transfer. The 5V USB bus power supply was intended to power peripherals that draw a maximum current of 500mA. Noise is of less importance as long as the peripheral works as intended.

As computer-based digital audio streaming became popular, USB was (mis)used for digital audio streaming. Because of related real-time data stream, there is no time for re-sending incorrect data. Incorrectly received data remains incorrect. USB audio devices are also highly sensitive to noise, this noise cannot be blocked as relatively large bandwidth interface is required to get the data through. Noise that falls within this digital audio interface bandwidth can enter the digital audio receiver and connected circuits like a DAC without any problems. Re-clockers won't help as these only attenuate jitter, not noise.

When the audio device is USB bus powered, it is important to keep this USB bus power supply as clean as possible. One could use a clean external mains power supply, but this would create an unwanted ground loop (PC -> mains -> mains power supply -> digital audio receiver -> USB interface -> PC) and may make matters worse.

Conventional USB interlinks have very thin wires (relatively high DC resistance). The data pairs are poorly twisted or not even twisted at all. This means that common mode noise isn't cancelled as intended and the data pairs emit electromagnetic interference. Data wire pairs and power supply wire pairs are running side by side without shield in between. This promotes crosstalk between both, data wiring and USB bus power supply wiring. When digital audio streaming starts, we get noise on both, data and USB bus power supply wiring. The varying load current creates an ac voltage drop across the power supply wires inside the interlink. This in turn creates an electromagnetic field that cross talks to the data wire pairs and vice versa. This is no problem for most peripherals and such construction keeps USB interlink price as low as possible.

USB interlinks intended for digital audio streaming can be improved by using individually shielded data and power supply wire pairs and higher quality wiring. This way unwanted crosstalk between both, data and USB bus power supply wiring can be minimised and Data transfer becomes more reliable.

Thicker wires (lower DC resistance) can be used to minimise ac voltage drop across the USB bus power supply wiring and ensure that the supply voltage at the USB audio receiver remains more stable.

We offer such an improved handcrafted USB audio interlink, it has individually screened data and USB bus power supply wiring, wiring is much thicker (lower DC resistance) and high quality cable is used (better dielectric). The wire we use has purple colour and has a diameter of 7mm, length equals 2.5 meters. It is recommended for USB DACs in general, and for use with U192ETL and UPL96ETL.