bryan wade / Mbed 2 deprecated usb_sound_effects

Streams USB audio with sound effects applied. Sound effect selected by joystick and intensity altered by tilting the mbed. Output to the mbed-application-board phono jack.

Dependencies:   C12832_lcd MMA7660 USBDevice mbed

/media/uploads/bw/img_1293.jpg 

/* Uses the mbed LPC1768 and mbed-application-board to create a USB audio device
 * that streams audio from a host computer to headphones or powered speakers. 
 * A couple different sound effects can be applied to the stream in real-time,
 * and tilting the mbed alters intensity of the effect.
 *
 *                                               ECHO
 *       The joystick selects )                   |
 *       one of three effect  )       STRAIGHT -  o  - STRAIGHT
 *       modes.               )                   |
 *                                              REVERB   
 * 
 *
 *
 *                                               \\           ||    
 *       Tilting the mbed     )      ======       \\          ||
 *       determines intensity )                    \\         ||
 *       of the effect.       )
 *                                     0%         50%         100%  
 *
 * The LCD display shows the current effect mode, intesity and buffer level.
*/

main.cpp@2:9429f84ea165, 2014-03-27 (annotated)

Committer:
bw
Date:
Thu Mar 27 21:43:41 2014 +0000
Revision:
2:9429f84ea165
Parent:
0:bbf6cf0eab95 
Clean up comments.

Who changed what in which revision?

UserRevisionLine numberNew contents of line
bw 0:bbf6cf0eab95 1 /*******************************************************************************
bw 0:bbf6cf0eab95 2 * Project: USB Sound Effects.
bw 0:bbf6cf0eab95 3 *
bw 0:bbf6cf0eab95 4 * Uses the mbed LPC1768 and mbed-application-board to create a USB audio device
bw 0:bbf6cf0eab95 5 * that streams audio from a host computer to headphones or powered speakers.
bw 0:bbf6cf0eab95 6 * A couple different sound effects can be applied to the stream in real-time,
bw 0:bbf6cf0eab95 7 * tilting the mbed alters the effects.
bw 0:bbf6cf0eab95 8 *
bw 0:bbf6cf0eab95 9 * ECHO
bw 0:bbf6cf0eab95 10 * The joystick selects ) |
bw 0:bbf6cf0eab95 11 * one of three effect ) STRAIGHT - o - STRAIGHT
bw 0:bbf6cf0eab95 12 * modes. ) |
bw 0:bbf6cf0eab95 13 * REVERB
bw 0:bbf6cf0eab95 14 *
bw 0:bbf6cf0eab95 15 *
bw 0:bbf6cf0eab95 16 *
bw 0:bbf6cf0eab95 17 * \\ ||
bw 0:bbf6cf0eab95 18 * Tilting the mbed ) ====== \\ ||
bw 0:bbf6cf0eab95 19 * determines intensity ) \\ ||
bw 0:bbf6cf0eab95 20 * of the effect. )
bw 0:bbf6cf0eab95 21 * 0% 50% 100%
bw 0:bbf6cf0eab95 22 *
bw 0:bbf6cf0eab95 23 * The LCD display shows the current effect mode, intesity and buffer level.
bw 0:bbf6cf0eab95 24 *
bw 0:bbf6cf0eab95 25 * For better audio quality, packets are buffered before playbeck. Playback is
bw 0:bbf6cf0eab95 26 * halted when the buffer drops below two packets and resumes when it is greater
bw 0:bbf6cf0eab95 27 * than four packets. This creates a lag of a few milliseconds, which is not
bw 0:bbf6cf0eab95 28 * detectable by a listener using straight playback mode.
bw 0:bbf6cf0eab95 29 *
bw 0:bbf6cf0eab95 30 * The echo effect produces echos with a delay of about 250 milliseconds. Tilting
bw 0:bbf6cf0eab95 31 * the mbed alters the persistence of echo.
bw 0:bbf6cf0eab95 32 *
bw 0:bbf6cf0eab95 33 * The reverb effect utilizes multiple delay lines of length varying from
bw 0:bbf6cf0eab95 34 * about 25 to 200 milliseconds. Again, tilting the mbed alters the
bw 0:bbf6cf0eab95 35 * persistence.
bw 0:bbf6cf0eab95 36 *
bw 0:bbf6cf0eab95 37 * Implemenation Notes:
bw 0:bbf6cf0eab95 38 * Audio playback is implement with an mbed ticker, and it is critical that this interrupt
bw 0:bbf6cf0eab95 39 * is not delayed to acheive decent audio quality. USB audio packet handling also uses
bw 0:bbf6cf0eab95 40 * interrupts, but the priority is set lower to ensure proper playback. The USBAudio class
bw 0:bbf6cf0eab95 41 * was modified to use a callback to transfer the received packet from the packet buffer to
bw 0:bbf6cf0eab95 42 * the larger playback buffer. The user interface is handled entirely in the user-context
bw 0:bbf6cf0eab95 43 * since it has only soft timing requirements.
bw 0:bbf6cf0eab95 44 *
bw 0:bbf6cf0eab95 45 * Future work:
bw 0:bbf6cf0eab95 46 * 1. Clocks within the host computer and mbed will differ slightly, so the
bw 0:bbf6cf0eab95 47 * average sample rate from the computer will not exactly match the average mbed
bw 0:bbf6cf0eab95 48 * playback rate. Over time the playback buffer level with creep until it becomes
bw 0:bbf6cf0eab95 49 * totaly empty or full. The current implementation addresses this by simply
bw 0:bbf6cf0eab95 50 * increasing the buffer size and selecting a sample rate that the mbed
bw 0:bbf6cf0eab95 51 * can replicate most accurately (mulitple of 1 us to use mbed Ticker). A better
bw 0:bbf6cf0eab95 52 * solution may be to slightly alter the playback rate in response to the buffer level.
bw 0:bbf6cf0eab95 53 * For example use 20us rate when the buffer level is high and 19us when the buffer
bw 0:bbf6cf0eab95 54 * level is low. Of course this would distort the playback frequecy by 5%, so it would
bw 0:bbf6cf0eab95 55 * be even better to make a custom timer interrupt with better resolution than the
bw 0:bbf6cf0eab95 56 * mbed ticker.
bw 0:bbf6cf0eab95 57 *
bw 0:bbf6cf0eab95 58 * 2. It would be interesting to add stereo audio, but the mbed-application-board
bw 0:bbf6cf0eab95 59 * audio jack is mono so this would require hardware customization.
bw 0:bbf6cf0eab95 60 *
bw 0:bbf6cf0eab95 61 * Bryan Wade
bw 0:bbf6cf0eab95 62 * 27 MAR 2014
bw 0:bbf6cf0eab95 63 ******************************************************************************/
bw 0:bbf6cf0eab95 64
bw 0:bbf6cf0eab95 65 #include "mbed.h"
bw 0:bbf6cf0eab95 66 #include "audio.h"
bw 0:bbf6cf0eab95 67 #include "effects.h"
bw 0:bbf6cf0eab95 68 #include "user_interface.h"
bw 0:bbf6cf0eab95 69
bw 0:bbf6cf0eab95 70 int main()
bw 0:bbf6cf0eab95 71 {
bw 2:9429f84ea165 72 UI_Initialize(); // Init the user interface.
bw 2:9429f84ea165 73 Audio_Initialize(); // Starts audio playback.
bw 0:bbf6cf0eab95 74
bw 0:bbf6cf0eab95 75 while (true)
bw 0:bbf6cf0eab95 76 {
bw 2:9429f84ea165 77 // Check the playback buffer level.
bw 0:bbf6cf0eab95 78 int32_t level = Audio_CheckPlaybackBufferLevel();
bw 2:9429f84ea165 79
bw 2:9429f84ea165 80 // Update the user interface, passing in the current buffer level
bw 2:9429f84ea165 81 // for display
bw 0:bbf6cf0eab95 82 UI_Update(level);
bw 0:bbf6cf0eab95 83
bw 2:9429f84ea165 84 // Set the effect mode and gain according to the user input.
bw 0:bbf6cf0eab95 85 Effects_SetMode(UI_GetEffectMode());
bw 2:9429f84ea165 86 Effects_SetGain(UI_GetEffectGain());
bw 0:bbf6cf0eab95 87
bw 2:9429f84ea165 88 // 50 milliseconds provides good UI responsivness.
bw 0:bbf6cf0eab95 89 wait(.05);
bw 0:bbf6cf0eab95 90 }
bw 0:bbf6cf0eab95 91 }
bw 0:bbf6cf0eab95 92