env.h

/*
 * Copyright 2017 Pascal Gauthier.
 * Copyright 2012 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
 
#pragma once
 
#include <stdint.h>
 
// DX7 envelope generation
 
#define ACCURATE_ENVELOPE
 
class EnvParams {
public:
    uint8_t rates[4];
    uint8_t levels[4];
};
 
class Env {
public:
    // The rates and levels arrays are calibrated to match the Dx7 parameters
    // (ie, value 0..99). The outlevel parameter is calibrated in microsteps
    // (ie units of approx .023 dB), with 99 * 32 = nominal full scale. The
    // rate_scaling parameter is in qRate units (ie 0..63).
    void init(const EnvParams& p, int outlevel, int rate_scaling);
    void update(const EnvParams& p, int outlevel, int rate_scaling);
 
    // Result is in Q24/doubling log format. Also, result is subsampled
    // for every N samples.
    // A couple more things need to happen for this to be used as a gain
    // value. First, the # of outputs scaling needs to be applied. Also,
    // modulation.
    // Then, of course, log to linear.
    int32_t getsample(const EnvParams& p, int n, int extra_rate);
    void keydown(const EnvParams& p, bool down);
    static int scaleoutlevel(int outlevel);
    void getPosition(char* step);
 
    static void init_sr(double sample_rate);
    void transfer(Env& src);
 
private:
    // PG: This code is normalized to 44100, need to put a multiplier
    // if we are not using 44100.
    static uint32_t sr_multiplier;
 
    // Level is stored so that 2^24 is one doubling, ie 16 more bits than
    // the DX7 itself (fraction is stored in level rather than separate
    // counter)
    int32_t level_;
    int targetlevel_;
    int ix_;
    int inc_;
#ifdef ACCURATE_ENVELOPE
    int staticcount_;
#endif
 
    int outlevel_;
    int rate_scaling_;
    bool down_;
    bool rising_;
 
    void advance(const EnvParams& p, int newix, int extra_rate);
};