annotate base/AudioLevel.h @ 1376:d9511f9e04d7 dev/refactor-piper-related

Introduce some POD structs for describing an external server application and the desired libraries to load from it, and disambiguating between empty list request and invalid list request. This allows for overriding PiperVampPluginFactory behaviour for using a PluginScan to populate the list request.

/* -*- c-basic-offset: 4 indent-tabs-mode: nil -*-  vi:set ts=8 sts=4 sw=4: */

/*
    Sonic Visualiser
    An audio file viewer and annotation editor.
    Centre for Digital Music, Queen Mary, University of London.
    
    This program is free software; you can redistribute it and/or
    modify it under the terms of the GNU General Public License as
    published by the Free Software Foundation; either version 2 of the
    License, or (at your option) any later version.  See the file
    COPYING included with this distribution for more information.
*/

/*
   This is a modified version of a source file from the 
   Rosegarden MIDI and audio sequencer and notation editor.
   This file copyright 2000-2006 Chris Cannam.
*/

#ifndef _AUDIO_LEVEL_H_
#define _AUDIO_LEVEL_H_

/**
 * AudioLevel converts audio sample levels between various scales:
 *
 *   - dB values (-inf -> 0dB)
 *   - floating-point values (-1.0 -> 1.0) such as used for a
 *     multiplier for gain or in floating-point WAV files
 *   - integer values intended to correspond to pixels on a fader
 *     or vu level scale.
 */

class AudioLevel
{
public:

    static const double DB_FLOOR;

    enum FaderType {
	     ShortFader = 0, // -40 -> +6  dB
              LongFader = 1, // -70 -> +10 dB
            IEC268Meter = 2, // -70 ->  0  dB
        IEC268LongMeter = 3, // -70 -> +10 dB (0dB aligns with LongFader)
	   PreviewLevel = 4
    };

    static double multiplier_to_dB(double multiplier);
    static double dB_to_multiplier(double dB);

    static double fader_to_dB(int level, int maxLevel, FaderType type);
    static int    dB_to_fader(double dB, int maxFaderLevel, FaderType type);

    static double fader_to_multiplier(int level, int maxLevel, FaderType type);
    static int    multiplier_to_fader(double multiplier, int maxFaderLevel,
				     FaderType type);

    // fast if "levels" doesn't change often -- for audio segment previews
    static int    multiplier_to_preview(double multiplier, int levels);
    static double preview_to_multiplier(int level, int levels);
};


#endif