Develop and Implementation of the

Speex Vocoder on the TI C64+ DSP

Students – Eyal Tirkel Roy Nahum

Supervisors – Prof. Ilan Shallom

Mr. Amir Artsi Mr. Guy Shterlich

Presentation Overview

• Subject covered :• Goal & Motivation• Speex Vocoder• DSP quick overview• TI C64x+ DSP• Optimization process• Optimization results so far

Project Goal

• Develop and Implement a Speech VoCoder, Speex, on the TI C64+ DSP• Probe the VoCoder and verify compatibility.• Analyze and profile the VoCoder for

complexity and real-time consumption of different parts in the code.

• Optimization in both C & Linear assembly for real-time processing with TI C64+ DSP.

Project Goal

Motivation

Speex

DSP

TI C64+

O. Process

O. Results

Codec

Codec

INTERNET

Motivation

• Usage of Internet Protocol (IP) for voice transfer is increasing rapidly, thus rising the need low bit-rate voice transmission while preserving quality.

• Reduce product costs :• Algorithm - Speex is patent-free.• Hardware - TI C64+ shelf fixed-point DSP.

Project Goal

Motivation

Speex

DSP

TI C64+

O. Process

O. Results

Speex - Overview

• Source-Filter Speech Model• Minimal info needed from past frame• CELP (Code Excited Linear Prediction)

algorithm• Analysis by Synthesis

Project Goal

Motivation

Speex

DSP

TI C64+

O. Process

O. Results

Source-Filter Speech Model

• The vocal cords are the source of sound (excitation signal)

• The vocal tract acts as a filter to spectrally shape the various sounds

Haaa

Project Goal

Motivation

Speex

DSP

TI C64+

O. Process

O. Results

Speex Codec Concept

• Excitation Generator – pattern selected by code • Filter - for Linear prediction

-Source S ignal ErrorTune Coeffi cients

Excitati on G eneratorFilter

D ecoder

Filter Coeffi cients

Excitati onCode

Encoded Coeffi cients

Speex A bS - Encoder

Project Goal

Motivation

Speex

DSP

TI C64+

O. Process

O. Results

DSP – Digital Signal Processor

• Multiple arithmetic units executing in parallel

• Dedicated arithmetic operations (MAC etc.)• SIMD (single instruction multiple data)

optimized• Memory streaming optimization (IDMA,

cache)• Hardware controlled looping• Hardware modulo addressing for circular

buffers• Saturation arithmetic

Project Goal

Motivation

Speex

DSP

TI C64+

O. Process

O. Results

TI C64+ DSP

• TI C64+ DSP Highlights

• Up to 8000 MIPS• Fixed-point architecture• 32-bit register size• VLIW architecture – Execute 8 instructions per

cycle• Two parallel data paths• 64 general-purpose registers• 8 functional units (2 Multipliers & 6 ALUs)• Internal DMA

Project Goal

Motivation

Speex

DSP

TI C64+

O. Process

O. Results

TI C64+ DSP

• TI C64+ DSP Block DiagramProject Goal

Motivation

Speex

DSP

TI C64+

O. Process

O. Results

TI C64+ DSP - example

• Paralleling Instructions:Project Goal

Motivation

Speex

DSP

TI C64+

O. Process

O. Results

Optimization process - Profiling

• TI Profiling tool outputProject Goal

Motivation

Speex

DSP

TI C64+

O. Process

O. Results

Optimization Process – Selecting functions

• Analyzing the profiling results can show which functions have a greater impact on overall performance.

inner_prod15%

compute_weighted_codebook13%

filter_mem1610%

iir_mem169%

vq_nbest7%

fir_mem165%

split_cb_search_shape_sign_N1

4%

others37%

Project Goal

Motivation

Speex

DSP

TI C64+

O. Process

O. Results

Optimization Process – Optimizing methods

• Sample optimization method

• Consider convolution :

• Can be coded like:

𝑦 [𝑛 ]=∑𝑚=1

𝑀

𝑥 [𝑚 ]h[𝑛−𝑚 ]

for (n=0; n<N; n++){

for (m=0; m<M; m++)

{

tempreg = tempreg + x[m] * h[n-m];

}y[n] =

tempreg;}

for (n=0; n<N; n++){

for (m=0; m<M; m++)

{y[n]

= y[n] + x[m] * h[n-m];

}}

Project Goal

Motivation

Speex

DSP

TI C64+

O. Process

O. Results

Optimization Results

compute_weighted_codeboo

k$1

filter_mem16 iir_mem16 vq_nbest fir_mem16

Not Opti-mized

48500 10056 8976.001042 6642.522292 14480

Compiler Optimized

17366 6665.010419 5048.68519 1989.522292 8592

Compiler and Manual Optimized

13267 649 448 994 563

5000.00

15000.00

25000.00

35000.00

45000.00

55000.00

Optimized functions

Cycle

s

Project Goal

Motivation

Speex

DSP

TI C64+

O. Process

O. Results

Optimization Results

• Encoder speed-up: 4.74• Decoder speed-up : 3.21

Project Goal

Motivation

Speex

DSP

TI C64+

O. Process

O. Results

nb_encode nb_decode

Not Optimized 71.62196783335 4.91694116665

Compiler Optimized 27.09871116665 2.37464433335

Compiler and Manual Optimized 15.0511385 1.52618583335

5.00

15.00

25.00

35.00

45.00

55.00

65.00

75.00

Average MCPS

MC

PS

Why the hard work?

• 1Ghz TI C64x+ DSP• Before: 13 concurrent voice calls• After: 60 concurrent voice calls

• Addition of 47 calls 460%

Thank You For Listening