1.11 usb_speaker_bass_boost

The Bass Boost audio enhancement is the 16 bit fixed-point implementation of a "Peak Shelving Filter", described by:

The Direct-Form 1 implementation (without scaling) is shown below:

The a0 scaling parameter can assumed to be 1, but for fixed point coefficient multiplies the right hand side coefficients should be scaled to fit into the required Q format. See LIBQ or CMIS-DSP library documentation for the defined Q formats for fixed point values required by the library.

The response of the filter for a bass boost of 6dB and a cutoff of 200Hz is shown below:

The gain is boosted below ~350 Hz and attenuated by -6dB above 800Hz, with a transition in between. the -6dB attenuation of the upper frequencies give headroom such that the boost does not overly saturate the audio output.

The usb_speaker_bass_boost demonstration uses multiples projects for multiple hardware configurations. MPLAB-X Harmony 3 projects only have one associated configurations. When each Harmony 3 project is created the MPLAB-X Code Configurator (MCC) code generation is guided by the processor that is selected.

Start MCC for the project in order to add the application code components. Both projects of the usb_speaker_bass_boost application use the USB Audio stack components. These can be added by selecting the Libraries/USB/Device Stack/Audio Function Driver component template under the MCC Available Components list, as shown below.

Answer yes to all questions. This loads the USB High Speed Driver, the USB Device Layer and Audio Function Driver components.

Additional MCC components for Math and Codec depend on the hardware configuration and are described in the next two sections.

The MCC Project Graph for usb_speaker_bass_boost is shown below.

In the MCC, under Available Components select the BSP PIC32 MZ EF Curiosity 2.0. Under Audio>Templates, double-click on AK4954 Codec Template (shown below). Answer Yes to all questions except for the one regarding FreeRTOS; answer No to that one. This loads the AK4954 Codec component along with associated I2C, I2S and timer driver components.

Select the Audio/Math/Math Libraries component to load the libq_c, libq/dsp libraries, as shown below:

The project configuration should now look something like this:

When building a new application, start by creating a 32-bit MPLAB Harmony 3 project in MPLAB X IDE by selecting File > New Project. Chose the Configuration name based on the BSP used. Select the appropriate processor (ATSAME70Q21B). Click Finish.

In the MCC, under Available Components select the appropriate BSP (SAM E70 Xplained Ultra). Under Audio>Templates, double-click on WM8904 Codec. Answer Yes to all questions except for the one regarding FreeRTOS; answer No to that one.

Select the Libraries/USB/Device Stack/Audio Function Driver component template, as shown below. Answer yes to all questions. This loads the USB High Speed Driver, the USB Device Layer and Audio Function Driver components.

To add the CMSIS-DSP Library to the project, select the CMSIS packs component.

The project configuration should look something like this:

The I2SC1 host requires the I2SC1_GCLK generate an MCLK to approximate 12.288Mhz. This is sourced using the PLLA Clock (PLLACK), as shown below.

USB Speaker I2S1 Bit Clock for 48Mhz operation

Using the PIC32 MZ EF Curiosity 2 and the AK4965 Daughter Board:

Click on the I2S2 Peripheral. Set the Frame Select Pin to C2. This is used to sense the start of the Left/Right bit frame clock.

Select the I2S driver and change the Transfer Queue Size to 64, as shown below:

Select the I2C1 component and select the Include Force Write I2C, This is required for the case where the AK4954 is in reset and does not respond with NACK when the I2C operation completes.

Using the PIC32 MZ EF Curiosity 2 with the AK4965 Daughter Board:

The LIBQ/DSP are used with MIPS MCU with microAptiv core require The default configuration of the audio/math/math libraries component is used, as shown below:

The DSP Library requires the LIBQ library to be selected.

Using the SAM E70 Xplained Ultra board and the WM8904 Audio Codec Daughter Board:

The CMSIS-DSP Library is optimized for use with the ARM M0-M7 MCU cores. It is selected using the CMSIS-Pack component (which is loaded automatically with the processor core component), as shown below:

All the needed drivers, middleware, libraries and application framework code can be generated from the MCC blocks (MCC components) placed in the MCC Project Graph.

The generated framework code is placed under the firmware/src/config directory under the name of the configuration used for the Harmony 3 project. The initial application code is located in the firmware/src directory app.c and app.h files, which utilize the framework drivers, middleware and library APIs located in definitions.h located in the config directory.

All Harmony applications first execute the SYS_Initialize function, located in initialization.c. This is executed from the main function to initialize various subsystems such as the clock, ports, BSP (board support package), codec, usb, timers, and interrupts. The application APP_Initialize function in app.c is executed last in the generated SYS_Initialize routine after the system initializations have completed.

The SYS_Tasks function (located in tasks.c) is used to update the USB subsystems, WM8904 driver, timers etc., as well as the application state machine (APP_tasks routine in app.c). This function is executed from the main polling loop. The polling loop either execute SYS_Tasks repeatably in the infinite loop to perform the updates, or it the updates occur as separate processes executed at fixed time intervals using an RTOS schedular.

The application utilizes a simple state machine (APP_Tasks executed from SYS_Tasks) with the following functions.

1. Setup the drivers and USB Library interface
2. Respond to USB Host control commands (Attach, Detach, Suspend)
3. Initiate and maintains the bidirectional data audio streaming for the "USB Playback" function

The parent folder for these files is audio/apps/usb_speaker_bass_boost. To build this project, you must open the audio/apps/usb_speaker_bass_boost/firmware/*.X project file in MPLAB X IDE that corresponds to your hardware configuration.

This table lists and describes the supported configurations of the demonstration, which are located within ./firmware/src/config.

Using the SAM E70 Xplained Ultra board and the WM8904 Audio Codec Daughter Board configured for the I2SC1 PLIB:

Jumper J203, which is next to the SAM E70 Xplained Ultra logo, should be jumpered for VBUS (not LED2).

To connect to the I2SC1, the jumpers (J6, J7, J8, and J9) on the WM8904 Codec Daughter board must be oriented toward the pink, mic in, connector.

Attach the WM8904 Daughter Board to the X32 connector and connect headphones to the green HP OUT jack, as shown in the figure below.

Headphone Out Jack is green. Microphone In Jack is pink.

As shown, the SAM E70 will be programmed via MPLAB-X through the USB cable connected to the EDBG micro-mini connector. Program debug can also be performed over USB this connection, if required.

Using the PIC32 MZ EF Curiosity 2 and the AK4965 Daughter Board:

The PIC32 MZ EF Curiosity board and the AK4954 Audio Codec Daughter Board only requires the AK4954 Codec Daughter board to be connected to X32 Header 2 as shown below. No jumper settings are required.

Headphone Out Jack is green. Microphone In Jack is pink.

Connect headphones to the green HP OUT jack of the Codec Daughter Board (as shown in the Figure above).

As shown, the SAM E70 will be programmed through the USB cable connected to the PKOB4 micro-mini connector. Program debug can also be performed over USB this connection.

Configure the board as described in the previous section. Attach either the EDBG or PKOB4 USB cable from the PC Host to the board, as described in the prior section.

To compile, select the appropriate MPLAB X IDE project configuration (see Table above). Compile and program the target device. Refer to Building the Application for details Do the following to run the demonstration:

1. After connecting a standard USB cable from the Host PC to either the EDBG or PKOB4 of the respective board, compile the application and program the target device. Run the device. The system will be in a waiting for the USB to be connected (LED1 off). The RGB LED on the Curiosity 2 board will run red, indicating no USB connection.
2. Connect a standard USB cable to the USB Host via the micro-mini connector located, either:
   • Above the push-button switches on the right side of the SAM E70 Xplained board, or
   • Above and to the left of the Reset switch on the PIC32 MZ EF Curiosity 2 board
3. Allow the Host computer to acknowledge, install drivers (if needed), and enumerate the device. No special software is necessary on the Host side.

LED1 will turn on as the USB function is enumerated (it may blink if audio is not streaming over the connection). The RGB LED on the Curiosity board will turn from red to green.

If needed, configure the Host computer to use the usb_speaker as the selected audio recording device. For Windows 7, this is done in the "Playback" tab in the "Sound" dialog accessed by right clicking the loudspeaker icon on the taskbar. For Windows 10, this is accessed by right clicking the loudspeaker icon on the taskbar and clicking Open Sound Settings. Select the Speaker( Harmony USB Speaker w/Bass Boost Example) as the default device. Now all sounds should be heard through the headphones.

1. Open a playback application (such as Window Media Player) and initiate playback, which should be heard throught the headphones.
2. Four volume levels are available, when pressing SWITCH 1. Initially, it is set to the lowest playback level. Pressing 2 more times will change the volume from the lowest to the highest playback level. Pressing 1 more time will mute audio and LED 1 will blink slowly. Pressing the button again will go back to the initial setting, from which the volume sequence began.
3. Bass Boost is demonstrated as follows:

Using the SAM E70 Xplained board and the WM8904 Daughter Board

A Long Press of SWITCH 1 will turn on Bass Boost. This will enhance (boost) the lower audio frequencies heard through the headphones. You can cycle from boosted audio to normal audio by repeating the Long Press of SWITCH1.

Using the PIC32 MZ EF Curiosity 2 and the AK4965 Daughter Board

Pressing SWITCH 2 will turn on LED 2 and the RGB LED will turn blue (indicating boost). The audio Bass Boost filter will be at its lowest level. Pressing SWITCH 2 repeatedly will cycle through 4 levels of Bass Boost (4, 6, 8, and 10 dB). A Long press of SWITCH 2 will turn off the Bass Boost, LED 2 will turn off and the RGB LED will turn green. Pressing again will turn on Bass Boost at the previous level.