delay.cpp

00001 /*******************************************************************************
00002  * Implements delay lines for audio samples.
00003  * Bryan Wade
00004  * 27 MAR 2014
00005  ******************************************************************************/
00006 #include "delay.h"
00007 #include "string.h"
00008 
00009 struct delay_t { // Implementation of opaque type.
00010     int16_t *base;
00011     int16_t *head;
00012     size_t len;
00013 };
00014 
00015 /*
00016  * Create a delay object given a ptr and size of available RAM.
00017  * This is only allocating memory for the metadata. The location of 
00018  * the buffer memory is passed in.
00019  * @return Ptr to the new delay.
00020  */
00021 delay_t *Delay_Create(void)
00022 {
00023     return (delay_t *)malloc(sizeof(delay_t));
00024 }
00025 
00026 /*
00027  * Configure delay buffer location and size.
00028  * @return True if successful.
00029  */
00030 bool Delay_Configure(delay_t *delay, void *ram, size_t size)
00031 {
00032     if (delay) {
00033         delay->base = delay->head = (int16_t *)ram;
00034         delay->len = size / sizeof(int16_t);
00035         memset(ram, 0, size);
00036         return true;
00037     }
00038     
00039     return false;
00040 }
00041 
00042 /*
00043  * Push a new sample with feedback into the delay while simulateously retieving the output sample.
00044  * @return Output data.
00045  */
00046 int16_t Delay_WriteWithFeedback(delay_t *delay, int16_t dataIn, uint16_t gain)
00047 {
00048     int16_t dataOut = *delay->head;
00049 
00050     // Feedback gain is fixed-point Q16 format.
00051     *delay->head = dataIn + ((gain * dataOut ) >> 16);
00052     
00053     if (++delay->head >= delay->base + delay->len)
00054         delay->head = delay->base;
00055         
00056     return dataOut;
00057 }
00058