Audio Processing Problems and Solutions2

Audio Processing Problems and Solutions2 - Microcomputer...

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Microcomputer Systems 1 Audio Processing Problems and Solutions
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Audio Processing Problems  and Solutions
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February 11, 2012 Veton Këpuska 3 Automatic Gain/Volume Control One of the simplest operations that can be performed in a  DSP on an audio signal is volume gain and attenuation.   For fixedpoint math, this operation can be performed by  multiplying each incoming sample by a fractional value  number between 0x0000…. and 0x7FFF…. or  using a shifter to multiply or divide the sample by a power of  2.  When increasing the gain of a signal, the programmer must  be aware of overflow, underflow, saturation, and quantization  noise effects.
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February 11, 2012 Veton Këpuska 4 Estimation of the Energy of the Signal Algorithm: Keep track of the maximum energy of the input signal. if (abs(in_sample) > myMax) { myMax = abs(sample); } Ajust the Gain to cover 80% of the overall dynamic range of the output. new_target_gain = 0.8*MAX_RANGE/myMax; Compute actual gain factor based on some empirically defined function  that performs necessary smoothing based on desired responsiveness  and smoothness of the gain. gain = compute_gain(gain, new_target_gain); Apply Gain: out_sample = gain*in_sample;
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February 11, 2012 Veton Këpuska 5 Gain Update Function float compute_gain(gain, new_gain) { // Linear interpolation float g, alpha = 0.2; // computed gain will adjust gain // each time is called by 20% toward // target gain g = (1-alpha)*gain + alpha*new_gain; return (g); }
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Amplitude Panning of Signals to a  Left or Right Stereo Field Reference: Using The Low Cost, High Performance ADSP-21065L Digital Signal Processor For Digital Audio Applications Dan Ledger and John Tomarakos DSP Applications Group, Analog Devices, Norwood, MA 02062, USA
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February 11, 2012 Veton Këpuska 7 Amplitude Panning of Signals to a  Left or Right Stereo Field In many applications, the DSP may need to process two (or  more) channels of incoming data, typically from a stereo A/D  converter.  Two-channel recording and playback is still the dominant  method in consumer and professional audio and can be found  in mixers and home audio equipment. V. Pulkki [22]  demonstrated placement of a signal in a stereo field (see  Figure 4 below) using Vector Base Amplitude Panning. The formulas presented in Pulkki’s paper for a two- dimensional trigonometric and vector panning will be shown  for reference.
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February 11, 2012 Veton Këpuska 8 Amplitude Panning of Signals to a  Left or Right Stereo Field Normally, the stereo signal will contain an exact duplicate of  the sampled input signal, although it can be split up to  represent two different mono sources. 
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This note was uploaded on 02/10/2012 for the course ECE 3551 taught by Professor Staff during the Spring '11 term at FIT.

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Audio Processing Problems and Solutions2 - Microcomputer...

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