This demo implements a USB audio mixer based on LPC55S69, and LPC55S69 is a USB composite device that can support
two USB audio speakers (Chat and Game speaker), a USB audio recoder and a HID device.This demo can support below features:
1. Support Full-speed USB and High-speed USB interface
2. Support UAC1.0 and UAC2.0
3. Support USB audio synchronous mode

Note:
1. USB HID class is not tested yet.

Hardware:
1. LPC55S69-EVK board
2. Two micro USB cables
3. 3.5mm headphone
4. PC
5. Double-ended 3.5mm audio cable for microphone test

Software:
1. IAR 9.60.2
2. windows media player or other audio player.


Test:
1. Select the desired working mode by setting macros in the usb_device_config.h file.
   #define USB_DEVICE_CONFIG_LPCIP3511FS (1U)
   #define USB_DEVICE_CONFIG_LPCIP3511HS (0U)
   #define USB_DEVICE_CONFIG_AUDIO_CLASS_2_0 (0U)
2. Compile this project and download it to LPC55S69 using the onboard debugger or an external debugger.
3. Press the RESET button S4 to run the program.
4. Play music on PC and select the correct audio speaker, can use one or two audio speaker
5. connect 3.5mm headphone to audio jack J2 and you can hear the mixed audio.
6. when testing microphone channel, need to connect the PC or other analog audio output and line-in jack (J1) of LPC55S69-EVK board using double-ended 3.5mm audio cable
   and play audio via line-in channel, then you can recorder the audio on PC and playback the recorded audio file.

