DelayA.h

#ifndef STK_DELAYA_H
#define STK_DELAYA_H

#include "Filter.h"

namespace stk {

/***************************************************/
/*! \class DelayA
    \brief STK allpass interpolating delay line class.

    This class implements a fractional-length digital delay-line using
    a first-order allpass filter.  If the delay and maximum length are
    not specified during instantiation, a fixed maximum length of 4095
    and a delay of 0.5 is set.

    An allpass filter has unity magnitude gain but variable phase
    delay properties, making it useful in achieving fractional delays
    without affecting a signal's frequency magnitude response.  In
    order to achieve a maximally flat phase delay response, the
    minimum delay possible in this implementation is limited to a
    value of 0.5.

    by Perry R. Cook and Gary P. Scavone, 1995--2023.
*/
/***************************************************/

class DelayA : public Filter
{
public:

  //! Default constructor creates a delay-line with maximum length of 4095 samples and delay = 0.5.
  /*!
    An StkError will be thrown if the delay parameter is less than
    zero, the maximum delay parameter is less than one, or the delay
    parameter is greater than the maxDelay value.
   */  
  DelayA( StkFloat delay = 0.5, unsigned long maxDelay = 4095 );

  //! Class destructor.
  ~DelayA();

  //! Clears all internal states of the delay line.
  void clear( void );

  //! Get the maximum delay-line length.
  unsigned long getMaximumDelay( void ) { return inputs_.size() - 1; };
  
  //! Set the maximum delay-line length.
  /*!
    This method should generally only be used during initial setup
    of the delay line.  If it is used between calls to the tick()
    function, without a call to clear(), a signal discontinuity will
    likely occur.  If the current maximum length is greater than the
    new length, no memory allocation change is made.
  */
  void setMaximumDelay( unsigned long delay );

  //! Set the delay-line length
  /*!
    The valid range for \e delay is from 0.5 to the maximum delay-line length.
  */
  void setDelay( StkFloat delay );

  //! Return the current delay-line length.
  StkFloat getDelay( void ) const { return delay_; };

  //! Return the value at \e tapDelay samples from the delay-line input.
  /*!
    The tap point is determined modulo the delay-line length and is
    relative to the last input value (i.e., a tapDelay of zero returns
    the last input value).
  */
  StkFloat tapOut( unsigned long tapDelay );

  //! Set the \e value at \e tapDelay samples from the delay-line input.
  void tapIn( StkFloat value, unsigned long tapDelay );

  //! Return the last computed output value.
  StkFloat lastOut( void ) const { return lastFrame_[0]; };

  //! Return the value which will be output by the next call to tick().
  /*!
    This method is valid only for delay settings greater than zero!
   */
  StkFloat nextOut( void );

  //! Input one sample to the filter and return one output.
  StkFloat tick( StkFloat input );

  //! Take a channel of the StkFrames object as inputs to the filter and replace with corresponding outputs.
  /*!
    The StkFrames argument reference is returned.  The \c channel
    argument must be less than the number of channels in the
    StkFrames argument (the first channel is specified by 0).
    However, range checking is only performed if _STK_DEBUG_ is
    defined during compilation, in which case an out-of-range value
    will trigger an StkError exception.
  */
  StkFrames& tick( StkFrames& frames, unsigned int channel = 0 );

  //! Take a channel of the \c iFrames object as inputs to the filter and write outputs to the \c oFrames object.
  /*!
    The \c iFrames object reference is returned.  Each channel
    argument must be less than the number of channels in the
    corresponding StkFrames argument (the first channel is specified
    by 0).  However, range checking is only performed if _STK_DEBUG_
    is defined during compilation, in which case an out-of-range value
    will trigger an StkError exception.
  */
  StkFrames& tick( StkFrames& iFrames, StkFrames &oFrames, unsigned int iChannel = 0, unsigned int oChannel = 0 );

protected:  

  unsigned long inPoint_;
  unsigned long outPoint_;
  StkFloat delay_;
  StkFloat alpha_;
  StkFloat coeff_;
  StkFloat apInput_;
  StkFloat nextOutput_;
  bool doNextOut_;
};

inline StkFloat DelayA :: nextOut( void )
{
  if ( doNextOut_ ) {
    // Do allpass interpolation delay.
    nextOutput_ = -coeff_ * lastFrame_[0];
    nextOutput_ += apInput_ + ( coeff_ * inputs_[outPoint_] );
    doNextOut_ = false;
  }

  return nextOutput_;
}

inline StkFloat DelayA :: tick( StkFloat input )
{
  inputs_[inPoint_++] = input * gain_;

  // Increment input pointer modulo length.
  if ( inPoint_ == inputs_.size() )
    inPoint_ = 0;

  lastFrame_[0] = nextOut();
  doNextOut_ = true;

  // Save the allpass input and increment modulo length.
  apInput_ = inputs_[outPoint_++];
  if ( outPoint_ == inputs_.size() )
    outPoint_ = 0;

  return lastFrame_[0];
}

inline StkFrames& DelayA :: tick( StkFrames& frames, unsigned int channel )
{
#if defined(_STK_DEBUG_)
  if ( channel >= frames.channels() ) {
    oStream_ << "DelayA::tick(): channel and StkFrames arguments are incompatible!";
    handleError( StkError::FUNCTION_ARGUMENT );
  }
#endif

  StkFloat *samples = &frames[channel];
  unsigned int hop = frames.channels();
  for ( unsigned int i=0; i<frames.frames(); i++, samples += hop ) {
    inputs_[inPoint_++] = *samples * gain_;
    if ( inPoint_ == inputs_.size() ) inPoint_ = 0;
    *samples = nextOut();
    lastFrame_[0] = *samples;
    doNextOut_ = true;
    apInput_ = inputs_[outPoint_++];
    if ( outPoint_ == inputs_.size() ) outPoint_ = 0;
  }

  return frames;
}

inline StkFrames& DelayA :: tick( StkFrames& iFrames, StkFrames& oFrames, unsigned int iChannel, unsigned int oChannel )
{
#if defined(_STK_DEBUG_)
  if ( iChannel >= iFrames.channels() || oChannel >= oFrames.channels() ) {
    oStream_ << "DelayA::tick(): channel and StkFrames arguments are incompatible!";
    handleError( StkError::FUNCTION_ARGUMENT );
  }
#endif

  StkFloat *iSamples = &iFrames[iChannel];
  StkFloat *oSamples = &oFrames[oChannel];
  unsigned int iHop = iFrames.channels(), oHop = oFrames.channels();
  for ( unsigned int i=0; i<iFrames.frames(); i++, iSamples += iHop, oSamples += oHop ) {
    inputs_[inPoint_++] = *iSamples * gain_;
    if ( inPoint_ == inputs_.size() ) inPoint_ = 0;
    *oSamples = nextOut();
    lastFrame_[0] = *oSamples;
    doNextOut_ = true;
    apInput_ = inputs_[outPoint_++];
    if ( outPoint_ == inputs_.size() ) outPoint_ = 0;
  }

  return iFrames;
}

} // stk namespace

#endif