JUCE/modules/juce_dsp/widgets/juce_Bias.h

/*
  ==============================================================================

   This file is part of the JUCE 6 technical preview.
   Copyright (c) 2020 - Raw Material Software Limited

   You may use this code under the terms of the GPL v3
   (see www.gnu.org/licenses).

   For this technical preview, this file is not subject to commercial licensing.

   JUCE IS PROVIDED "AS IS" WITHOUT ANY WARRANTY, AND ALL WARRANTIES, WHETHER
   EXPRESSED OR IMPLIED, INCLUDING MERCHANTABILITY AND FITNESS FOR PURPOSE, ARE
   DISCLAIMED.

  ==============================================================================
*/

namespace juce
{
namespace dsp
{

/**
    Adds a DC offset (voltage bias) to the audio samples.

    This is a useful preprocessor for asymmetric waveshaping when a waveshaper is
    bookended by a bias on input and a DC-offset removing high pass filter on output.

    This is an extremely simple bias implementation that simply adds a value to a signal.
    More complicated bias behaviours exist in real circuits - for your homework ;).

    @tags{DSP}
*/
template <typename FloatType>
class Bias
{
public:
    Bias() noexcept = default;

    //==============================================================================
    /** Sets the DC bias
        @param newBias DC offset in range [-1, 1]
    */
    void setBias (FloatType newBias) noexcept
    {
        jassert (newBias >= static_cast<FloatType> (-1) && newBias <= static_cast<FloatType> (1));
        bias.setTargetValue (newBias);
    }

    //==============================================================================
    /** Returns the DC bias
        @return DC bias, which should be in the range [-1, 1]
    */
    FloatType getBias() const noexcept              { return bias.getTargetValue(); }

    /** Sets the length of the ramp used for smoothing gain changes. */
    void setRampDurationSeconds (double newDurationSeconds) noexcept
    {
        if (rampDurationSeconds != newDurationSeconds)
        {
            rampDurationSeconds = newDurationSeconds;
            updateRamp();
        }
    }

    double getRampDurationSeconds() const noexcept  { return rampDurationSeconds; }

    //==============================================================================
    /** Called before processing starts */
    void prepare (const ProcessSpec& spec) noexcept
    {
        sampleRate = spec.sampleRate;
        updateRamp();
    }

    void reset() noexcept
    {
        bias.reset (sampleRate, rampDurationSeconds);
    }

    //==============================================================================
    /** Returns the result of processing a single sample. */
    template <typename SampleType>
    SampleType processSample (SampleType inputSample) noexcept
    {
        return inputSample + bias.getNextValue();
    }

    //==============================================================================
    /** Processes the input and output buffers supplied in the processing context. */
    template<typename ProcessContext>
    void process (const ProcessContext& context) noexcept
    {
        auto&& inBlock  = context.getInputBlock();
        auto&& outBlock = context.getOutputBlock();

        jassert (inBlock.getNumChannels() == outBlock.getNumChannels());
        jassert (inBlock.getNumSamples()  == outBlock.getNumSamples());

        auto len         = inBlock.getNumSamples();
        auto numChannels = inBlock.getNumChannels();

        if (context.isBypassed)
        {
            bias.skip (static_cast<int> (len));

            if (context.usesSeparateInputAndOutputBlocks())
                outBlock.copyFrom (inBlock);

            return;
        }

        if (numChannels == 1)
        {
            auto* src = inBlock.getChannelPointer (0);
            auto* dst = outBlock.getChannelPointer (0);

            for (size_t i = 0; i < len; ++i)
                dst[i] = src[i] + bias.getNextValue();
        }
        else
        {
            auto* biases = static_cast<FloatType*> (alloca (sizeof (FloatType) * len));

            for (size_t i = 0; i < len; ++i)
                biases[i] = bias.getNextValue();

            for (size_t chan = 0; chan < numChannels; ++chan)
                FloatVectorOperations::add (outBlock.getChannelPointer (chan),
                                            inBlock.getChannelPointer (chan),
                                            biases, static_cast<int> (len));
        }
    }


private:
    //==============================================================================
    SmoothedValue<FloatType> bias;
    double sampleRate = 0, rampDurationSeconds = 0;

    void updateRamp() noexcept
    {
        if (sampleRate > 0)
            bias.reset (sampleRate, rampDurationSeconds);
    }
};

} // namespace dsp
} // namespace juce