![]() All of these 'standard' classes are defined in the USB specification, which you can download from usb.org. The way USB is designed, a single device can implement several classes simultaneously. For that reason, many of these controllers implement both Audio and HID classes, usually so you can attach buttons to the DAC and control the volume in the OS via HID. USB Audio Class devices implement audio transfer, but nothing else. For example HID is the class used for human interface devices, this class provides for keyboards, mice, and is generic enough that it's often used for simple I/O. To clarify things a bit, USB has 'device classes' which specify the interface for certain standard types of gizmos. I don't think they make any with I2S both in and out, but I'm not 100% sure. TI also makes PCM29xx series which are CODECs. Here are some resources that I have found: The only reason I mention the Teensy so much is that it is the only board I have heard of that can be a custom USB device but I would be willing to go to any other solution. Also I know for sure that the Teensy 2.0++ can be a HID Keyboard, Mice, Joystick and MIDI, but I want to know if the Teensy 3.0 has this same capability as well. I do not see any documentation on implementing an audio device besides the MIDI article but maybe the USB serial feature is able to send the audio stream data. Relatively recently, I saw the Teensy used in a project to make a custom game controller. I am going to be using this mixer / interface on a Windows machine but it would be nice if it used some specification of USB to be compatible with all OS without an external driver (Plug and Play). This of course would probably be possible through the I/O. Most of my experience comes from FPGA's (Digilent Basys2 and Atlys) and I think that the Digilent SDK can is only good for transferring bits and not emulating a USB device. I am not sure if those cards are classified as a HID or just Audio device or if that is the spec that Windows uses to auto identify a microphone or speaker but that is what I am looking for. ![]() I recently got a cheapy USB sound card (ebay search "usb sound card") from China just to see what is going on and they seem to be able to implement this in a tiny, super low cost solution. Most of the existing audio mixers cost hundreds of dollars and I am looking for a relatively low cost DIY solution. I have been interested in making a USB 3.5mm mixer with multiple input/output channels but have not been able to find the starting point or dev board that will be able to accomplish this task.
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