refactor: Move chunkware to third_party

third_party/chunkware_dsp/SimpleLimitProcess.inl

@@ -0,0 +1,139 @@
+/*
+ *	Simple Limiter (runtime function)
+ *
+ *  File		: SimpleLimitProcess.inl
+ *	Library		: SimpleSource
+ *  Version		: 1.12
+ *  Implements	: void SimpleLimit::process( double &in1, double &in2 )
+ *
+ *	2006, ChunkWare Music Software, OPEN-SOURCE
+ *
+ *	Permission is hereby granted, free of charge, to any person obtaining a
+ *	copy of this software and associated documentation files (the "Software"),
+ *	to deal in the Software without restriction, including without limitation
+ *	the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ *	and/or sell copies of the Software, and to permit persons to whom the
+ *	Software is furnished to do so, subject to the following conditions:
+ *
+ *	The above copyright notice and this permission notice shall be included in
+ *	all copies or substantial portions of the Software.
+ *
+ *	THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ *	IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ *	FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ *	THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ *	LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ *	FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ *	DEALINGS IN THE SOFTWARE.
+ */
+
+
+#ifndef __SIMPLE_LIMIT_PROCESS_INL__
+#define __SIMPLE_LIMIT_PROCESS_INL__
+
+namespace chunkware_simple
+{
+	//-------------------------------------------------------------
+	INLINE void SimpleLimit::process( double &in1, double &in2 )
+	{
+		// create sidechain
+
+		double rect1 = fabs( in1 );	// rectify input
+		double rect2 = fabs( in2 );
+
+		double keyLink = std::max( rect1, rect2 );	// link channels with greater of 2
+
+		// threshold
+		// we always want to feed the sidechain AT LEATS the threshold value
+		if ( keyLink < thresh_ )
+			keyLink = thresh_;
+
+		// test:
+		// a) whether peak timer has "expired"
+		// b) whether new peak is greater than previous max peak
+		if ( (++peakTimer_ >= peakHold_) || (keyLink > maxPeak_) ) {
+			// if either condition is met:
+			peakTimer_ = 0;		// reset peak timer
+			maxPeak_ = keyLink;	// assign new peak to max peak
+		}
+
+		/* REGARDING THE MAX PEAK: This method assumes that the only important
+		 * sample in a look-ahead buffer would be the highest peak. As such,
+		 * instead of storing all samples in a look-ahead buffer, it only stores
+		 * the max peak, and compares all incoming samples to that one.
+		 * The max peak has a hold time equal to what the look-ahead buffer
+		 * would have been, which is tracked by a timer (counter). When this
+		 * timer expires, the sample would have exited from the buffer. Therefore,
+		 * a new sample must be assigned to the max peak. We assume that the next
+		 * highest sample in our theoretical buffer is the current input sample.
+		 * In reality, we know this is probably NOT the case, and that there has
+		 * been another sample, slightly lower than the one before it, that has
+		 * passed the input. If we do not account for this possibility, our gain
+		 * reduction could be insufficient, resulting in an "over" at the output.
+		 * To remedy this, we simply apply a suitably long release stage in the
+		 * envelope follower.
+		 */
+
+		// attack/release
+		if ( maxPeak_ > env_ )
+			att_.run( maxPeak_, env_ );		// run attack phase
+		else
+			rel_.run( maxPeak_, env_ );		// run release phase
+
+		/* REGARDING THE ATTACK: This limiter achieves "look-ahead" detection
+		 * by allowing the envelope follower to attack the max peak, which is
+		 * held for the duration of the attack phase -- unless a new, higher
+		 * peak is detected. The output signal is buffered so that the gain
+		 * reduction is applied in advance of the "offending" sample.
+		 */
+
+		/* NOTE: a DC offset is not necessary for the envelope follower,
+		 * as neither the max peak nor envelope should fall below the
+		 * threshold (which is assumed to be around 1.0 linear).
+		 */
+
+		// gain reduction
+		double gR = thresh_ / env_;
+
+		// unload current buffer index
+		// ( cur_ - delay ) & mask_ gets sample from [delay] samples ago
+		// mask_ variable wraps index
+		unsigned int delayIndex = ( cur_ - peakHold_ ) & mask_;
+		double delay1 = outBuffer_[ 0 ][ delayIndex ];
+		double delay2 = outBuffer_[ 1 ][ delayIndex ];
+
+		// load current buffer index and advance current index
+		// mask_ wraps cur_ index
+		outBuffer_[ 0 ][ cur_ ] = in1;
+		outBuffer_[ 1 ][ cur_ ] = in2;
+		++cur_ &= mask_;
+
+		// output gain
+		in1 = delay1 * gR;	// apply gain reduction to input
+		in2 = delay2 * gR;
+
+		/* REGARDING THE GAIN REDUCTION: Due to the logarithmic nature
+		 * of the attack phase, the sidechain will never achieve "full"
+		 * attack. (Actually, it is only guaranteed to achieve 99% of
+		 * the input value over the given time constant.) As such, the
+		 * limiter cannot achieve "brick-wall" limiting. There are 2
+		 * workarounds:
+		 *
+		 * 1) Set the threshold slightly lower than the desired threshold.
+		 *		i.e. 0.0dB -> -0.1dB or even -0.5dB
+		 *
+		 * 2) Clip the output at the threshold, as such:
+		 *
+		 *		if ( in1 > thresh_ )		in1 = thresh_;
+		 *		else if ( in1 < -thresh_ )	in1 = -thresh_;
+		 *
+		 *		if ( in2 > thresh_ )		in2 = thresh_;
+		 *		else if ( in2 < -thresh_ )	in2 = -thresh_;
+		 *
+		 *		(... or replace with your favorite branchless clipper ...)
+		 */
+	}
+
+}	// end namespace chunkware_simple
+
+#endif	// end __SIMPLE_LIMIT_PROCESS_INL__