AudioDelay.h

/*
 * AudioDelay.h
 *
 * Copyright 2012 Tim Barrass.
 *
 * This file is part of Mozzi.
 *
 * Mozzi is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.
 *
 */

#ifndef AUDIODELAY_H_
#define AUDIODELAY_H_


/** Audio delay line for comb filter, flange, chorus and short echo effects.
@tparam  NUM_BUFFER_SAMPLES is the length of the delay buffer in samples.  This should
be a power of two. The largest delay you'll fit in an atmega328 will be 512
cells, which at 16384 Hz sample rate is 31 milliseconds. More of a flanger or a
doubler than an echo. The amount of memory available for delays on other chips will vary.
AudioDelay() doesn't have feedback.  If you want feedback, use AudioDelayFeedback().
@tparam the type of numbers to use for the signal in the delay.  The default is int8_t, but int could be useful
when adding manual feedback.  When using int, the input should be limited to 15 bits width, ie. -16384 to 16383.
*/

template <unsigned int NUM_BUFFER_SAMPLES, class T = int8_t>
class AudioDelay
{

private:

    T delay_array[NUM_BUFFER_SAMPLES];
    unsigned int _write_pos;
    unsigned int _delaytime_cells;

public:

    /** Constructor.
    */
    AudioDelay(): _write_pos(0)
    {}


    /** Constructor.
    @param delaytime_cells delay time expressed in cells.  
    For example, 128 cells delay at AUDIO_RATE would produce a time delay of 128/16384 = 0.0078125 s = 7.8 ms
    Put another way, num_cells = delay_seconds * AUDIO_RATE.
    */
    AudioDelay(unsigned int delaytime_cells): _write_pos(0), _delaytime_cells(delaytime_cells)
    {}



    /** Input a value to the delay and retrieve the signal in the delay line at the position delaytime_cells.
    @param in_value the signal input.
    @param delaytime_cells sets the delay time in terms of cells in the delay buffer.
    */
    inline
    T next(T in_value, unsigned int delaytime_cells)
    {
        ++_write_pos &= (NUM_BUFFER_SAMPLES - 1);
        unsigned int read_pos = (_write_pos - delaytime_cells) & (NUM_BUFFER_SAMPLES - 1);

        // why does delay jump if I read it before writing?
        delay_array[_write_pos] = in_value;         // write to buffer
        int8_t delay_sig = delay_array[read_pos] ;  // read the delay buffer

        return (T)delay_sig;
    }



    /** Input a value to the delay and retrieve the signal in the delay line at the position delaytime_cells.
    @param in_value the signal input.
    */
    inline
    T next(T in_value)
    {
        ++_write_pos &= (NUM_BUFFER_SAMPLES - 1);
        unsigned int read_pos = (_write_pos - _delaytime_cells) & (NUM_BUFFER_SAMPLES - 1);

        // why does delay jump if I read it before writing?
        delay_array[_write_pos] = in_value;         // write to buffer
        T delay_sig = delay_array[read_pos] ;   // read the delay buffer

        return delay_sig;
    }


    /** Set the delay time, measured in cells.
    @param delaytime_cells how many cells to delay the input signal by.
    */
    inline
    void set(unsigned int delaytime_cells){
        _delaytime_cells = delaytime_cells;
    }


    /** Retrieve the signal in the delay line at the position delaytime_cells.
    It doesn't change the stored internal value of _delaytime_cells.
    @param delaytime_cells indicates the delay time in terms of cells in the delay buffer.
    */
    inline
    T read(unsigned int delaytime_cells)
    {
        unsigned int read_pos = (_write_pos - delaytime_cells) & (NUM_BUFFER_SAMPLES - 1);
        return delay_array[read_pos];
    }


    // /** Input a value to the delay but don't advance the write position, change the delay time or retrieve the output signal.
    // This can be useful for manually adding feedback to the delay line, "behind" the advancing write head.
    // @param input the signal input.
    // */
    // inline
    // void writeFeedback(T input)
    // {
        // delay_array[_write_pos] = input;
    // }

};

/**
@example 09.Delays/AudioDelay/AudioDelay.ino
This is an example of how to use the AudioDelay class.
*/

#endif        //  #ifndef AUDIODELAY_H_