Linear Predictive Coding in Mixed-Excitation Linear Predictive Coder - MELP

4/25/2020

MELP LPC LSFs demonstration

Subject:

Adaptive Digital Signal Processing

Scientific Postgraduate Study of Electronics, FESB, University of Split Professor:

dr. sc. Dinko Begušić

Student:

Zoran Sambol

LPC impact on MELP 1

Adaptive DSP - Study

 Subject program  Literature - Simon Haykin: Adaptive filter theory, Prentice Hall, 1991.

 Practical work based on MELP codec  Study subject – Speech coding Presentation  Three phases  Adaptive Filter theory – Seminar documents   MELP codec adjustment - coding LPC LSF impact on MELP – today presentation 4/25/2020 LPC impact on MELP 2

LPC – show impact on MELP

 Task was given during MELP codec presentation – September 2002.

 MELP codec is based on Linear Predictive Coding.

 Its LPC coder has 10 th order  My task was to show impact of LPC coder on overall MELP algorithm 4/25/2020 LPC impact on MELP 3

LPC web & resources

 MELP documents - MELP Presentation page 3.

 DDVPC Homepage,

Standard draft

, ASPI digital – Polycom, Texas Instruments and

Noam Amir educational site

.

  Most of the resources has samples coded in

Matlab

Google groups search – Line Spectrum Pairs (LSP)  Cite – William M. Wiese Jr.

[ In the real world, if two adjoining LSF values are equal we separate them by some small value like 35 – 50 Hz.]

What will happen if I change LSF that minimum distance is greater or less than 50 Hz?

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Encoder MELP – LPC

Speech Signal Hamming Window (200 samples) LPC Filter Residual Signal Autocorrelation function Levinson-Durbin recursion uses Toeplitz 10 LP coefficeints

1) VOICING ANALYSIS (peakines calculation)

10 LPC -> 10 LSF 10 predicton coefficients 10 LSF ascending order Bandwith expansion

2) Final PITCH calculation

3) FOURIER MAGNITUDE

calculation

MSVQ (multi state vector quantization) Array of vectors Quantizied LSF vector LSF vector Separation algorithm (50 Hz) Separation algorithm (50 Hz)

Quantization of prediction coefficients

Quantizing predictor coeficients Generating the residual window

Fourier Magnitude calculation & quantization

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Decoder MELP - LPC

Bit unpacking and FEC 10 LSF check for ascending order and minimum separation Parameter Interpolation Interpolated LSFs LPC Synthesis 4/25/2020 LPC filter coefficients

Parameters

LSF’s Fourier Magnitudes Gain (2 per frame) Pitch (overall voicing) Bandpass voicing Aperiodic Flag Error protection Sync Bit Total bits/ 22.5 ms Frame

Voiced 25 8

8

7 4

1 1

54

Unvoiced

25 8 7 13 1 54 Adaptive Spectral Enhancment 1 st Reflection Coefficient LPC impact on MELP 44/54 = 81.48% 6

MELP codec

 Windows console application  What were changed?

 Command prompt – additional argument 

ConsoleMelp –a –i dam9.bin –o dam9.ccl –f 150

 Parse function

- void parse(int argc,char **argv)

 Clamping function (sort LSFs and minimum separation) 

int lpc_clmp(float *w, float delta, int p);

 Minimum LSF separation   #define BWMIN (50.0*2/FSAMP) /* minimum LSF separation */ Changed with

float fLSFFrequency

variable 4/25/2020 LPC impact on MELP 7

Recorder - Player

 Windows

MELPCodec

application  Known interface  Equalizer dialog  50 Hz default value  Check button  Log slider  Easy canceling Equalizer LPC impact on MELP 4/25/2020 8

Batch – Console applications

 Four different console application integrated using DOS Batch files  Waveopt, ConsoleMelp, CCRemover and CCInserter  Console applications with input and output parameters – files 

ConsoleMelp –a –i dam9.bin –o dam9.ccl –f 150

 

Waveopt

syntax:  Waveopt.exe [*.bin | *.wav] Easy deleting, renaming, directory creating –  Read Me file .

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Testing

 Well known record  Using MelpCodec application as a recorder and my own voice.

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Results

 Subjective measurements  Overvoicing  Quality degradation – Male and Female  180 samples segments impact on parameters  Real measurement – MOS (ITU) 4/25/2020 LPC impact on MELP 11

Windows – MELP Codec

 Opening WAV and MELP (Channel coded) files  Playing files  Recording and storing waves in MELP useful format  Recording Channel coded and MELP files  Size comparison - Explorer utility  Useful Equalizer 4/25/2020 LPC impact on MELP 12

MelpCodec with Equalizer

Education

      Useful adjustable tool:    Statistics (MOS, DAM, DRT measurement) Vocoder example for FEC Internet and database connection  Visualization, Skins and additional GUI components Laboratory exercise – Voice Coding subject Digital Signal Adaptive Processing - Subject Gathering measurement results Symposium article (IEEE, SoftCOM, ELMAR, MiPRO) Experience for some other voice and no-voice LP algorithms 4/25/2020 LPC impact on MELP 13

Thanks for your time!

Contact:

Zoran Sambol, Siemens d.d. Put Brodarice 6, 21000 Split Tel. +385 21 390 936

[email protected]

, [email protected]

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