USB audio devices have stronger requirements for USB hardware and software layers than other USB devices. A faulty hardware component, e.g. USB cable or USB port, may not have an impact on standard USB devices such as a FLASH drive but can be catastrophic for a USB audio device. USB hardware requirements are discussed in more detail in the section 4. Due to the real-time nature of USB audio streams there are also requirements for time characteristic of the operating system and third party software components installed on the system. Software components that make real-time behavior of the operating system worse are not compatible with audio streaming applications in general. However, in this context it’s important to note that real-time requirements depend directly on audio latency requirements. If low audio latency is required (e.g. to create a monitor mix in the PC and route it back to speakers) then the operating system must be able to fulfill resulting timing requirements of the driver. If audio latency is not critical (e.g. in case of music playback) then timing requirements of the driver are relaxed which increases compatibility with other applications and drivers significantly. AMI Muse DDH-1 driver allows users to adjust internal buffer depths to find a tradeoff between audio latency and compatibility with a given system. Below, two typical scenarios are discussed.
(1) Low-latency applications
Audio latency is critical if an audio signal is routed into the PC, processed in the PC and then routed back to speakers. A typical scenario is a monitor mix created by a multi-track recording application such as Cubase. For such applications the drivers streaming buffer depth should be set to 4 milliseconds or less. In this configuration a couple of issues can occur because the given system may not be able to handle the resulting real-time requirements. A discussion of possible problems and incompatibilities is given in section 3.
(2) Normal-latency applications
In case of a playback-only or recording-only scenario, audio latency is not critical. For such applications the driver’s streaming buffer depth should be set to 16 milliseconds or more. This will reduce the risk of audio distortions caused by other software components in the system significantly. Issues discussed in section 5 may still occur but this will happen in extreme cases only. If the driver is configured this way, it will be compatible with a larger number of Windows systems. Normally, it will not be necessary to optimize a system for audio steaming according to the hints given in “known software issue and possible solutions”.