Digital Signal Processing Solutions Abstract filters describ

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Programmable Double Biquad Filter Tone Detection Fixed Point DSPs
Digital Signal Processing Solutions
Abstract
filters described here user programmable double biquad filters tone detection. filters implemented Texas Instruments TMS320C2xx digital signal processor (DSP). filter program includes energy estimation stage. Examples applications CPTD (call progress tone detection), tone detection, answer tone detection, etc. telephony modem.
Contents
Introduction Filter Structure Difference Equations Description Tone Detection Procedure Description Filter Programs.5 initFilt.c Biquad.asm Summary Programmable Parameters.8 Interface Between High Level Programs Filter Program Processor Resources Used Filter Programs Reference Appendix Source Code.11 FILE: BIQUAD.ASM.11 FILE: INITFILT.C.18 FILE: FILTERS.H Appendix Glossary.23
Figures
Figure Figure Figure Figure Figure Transposed Form Cascade Structure Stages Tone Detection Operation Example Filter Design Dial Tone Detector Flow Chart Decision Stage Detection Process Cadence Check Busy Tone Detection
Tables
Table Table Table Table Masks Different Filters.7 Scale Factors Corresponding Right Shift Input Sample Detection Thresholds Corresponding Energy Fraction.9 Processor Resources Required Tone Detection Module
Digital Signal Processing Solutions
February 1999
Introduction
this report describe tone detection means programmable passband filter combination with energy estimation stage. filtering operation described below allows detection single frequencies (with tolerance band ±x%) frequency band (e.g., tones used telephone net: dial tone, busy tone, etc.). parameters related tone detection process user programmable. These parameters include filter coefficients, scale factors detection thresholds. following sections describe filter structure used passband filtering different steps involved detection process, software carrying these operations, interface between filter programs application layer processor resources required.
Filter Structure Difference Equations
This section gives theoretical overview filter used tone detection process. filter structure implemented here so-called transposed form cascade structure, which shown Figure
Figure Transposed Form Cascade Structure
x[n] y1[n] d11[n] -a11 d12[n] -a12 y[n]
d21[n] -a21 d22[n] -a22
corresponding difference equations are:
1,2,.,
(equation
+1)/
x[n] denotes filter input, yi[n] filter output after filter stage y[n] global filter output. means filter design tool using filter structure shown Figure determine filter coefficients double biquad filter (N=4) desired passband. example filter design will given next section.
Programmable Double Biquad Filter Tone Detection Fixed Point DSPs
Description Tone Detection Procedure
tone detection procedure divided into different stages shown Figure
Figure Stages Tone Detection Operation
y[n] x[n] Scale x[n] Energy estimation based |y[n]|
Decision
Energy estimation based |x[n]|
First main filtering operation carried out. This consists bandpass filtering scaled input signal. This followed energy estimation means exponential filters based filtered signal global signal. exponential filters given
FilterOut y[n] FilterOut TotOut[n] TotOut
(equation
last stage consists decision whether tone been detected not. detection criteria specified follows
FilterOut[n] Threshold TotOut
(equation
bandpass filter double biquad filter based equation filter coefficients have previously determined means filter design tool. bandpass filter characterized seven parameters: sampling frequency, lower upper stopband frequencies lower upper passband frequencies, well passband ripple stopband ripple. example filter design shown Figure filter coefficients generated design tool stored C-header file, Filters.h. Before running filter first time, initialization routines contained file initFilt.c have executed. different programs interface C-Assembly language will described following sections.
Programmable Double Biquad Filter Tone Detection Fixed Point DSPs
Figure Example Filter Design Dial Tone Detector
Sampling frequency Fs=9.6kHz Lower stopband frequency=365Hz Lower passband frequency=425Hz Upper passband frequency=455Hz Upper stopband frequency=515Hz
Passband ripple=0.1 Stopband ripple=0.03
INFINITE IMPULSE RESPONSE (IIR),ELLIPTIC BANDPASS FILTER UNQUANTIZED COEFFICIENTS, FILTER ORDER SAMPLING FREQUENCY 9.600 KILOHERTZ A(I,1) -1.903748 -1.913757 A(I,2) .990570 991089 B(I,0) .144363 .141541 B(I,1) -.270309 -.275604 B(I,2) .144363 .141541
DialFilter*/ Quantized coefficients: Coefficients biquad #define Dial1_B0 2365 #define Dial1_B1 -4428 #define Dial1_B2 2365 #define Dial1_A1 31191 #define Dial1_A2 -16229
Coefficients biquad #define Dial2_B0 #define Dial2_B1 #define Dial2_B2 #define Dial2_A1 #define Dial2_A2
2319 -4515 2319 31356 -16238
Programmable Double Biquad Filter Tone Detection Fixed Point DSPs
Description Filter Programs
This section deals with filter programs parameters that have determined before running filter. parameters that directly influence detection programmable. These parameters include filter coefficients, scale factor input sample applied filter detection threshold. They found file Filters.h, given Appendix This file used initialization routine initFilt.c, described below. example, filter dial busy tone detection implemented.
initFilt.c
This routine initializes filter variables with fixed parameter values. variable names chosen according following convention: FilterNameVariable. Example: filter name=Dial, variable=Threshold variable name=DialThreshold. Each filter following variables: -Filter[14]: Array fourteen elements filter coefficients delays -Shift: Scale factor input sample -Threshold: Factor used decision stage (cf. equation -In: Input exponential filter after bandpass filtering (|y[n]|) -Out: Output exponential filter applied decision stage where stands filter name. elements -Filter[14] double biquad shown Figure are: -Filter[0]=d11 -Filter[1]=d12 -Filter[2]=d21 -Filter[3]=d22 -Filter[4]=b10 -Filter[5]=b11 -Filter[6]=-a11 -Filter[7]=-a12 -Filter[8]=b12 -Filter[9]=b21 -Filter[10]=b22 -Filter[11]=-a21 -Filter[12]=-a22 -Filter[13]=b22 delays through initialized zero. elements -Filter[4] through -Filter[13] initialized with filter coefficients specified Filters.h. Likewise -Shift -Threshold specified parameter values. input output exponential filters initialized zero.
Biquad.asm
file biquad.asm contains different stages filtering operation described Figure Several filters implemented parallel. Currently, examples dial tone tone detection implemented. routine that calls filters named CPTD. This routine called sample interrupt (sampling frequency), which implies that filter design been previously carried with same sampling frequency.
Programmable Double Biquad Filter Tone Detection Fixed Point DSPs
tone detection process, absolute value input sample first computed estimation global energy. case filters being implemented parallel, exponential filter based absolute values input samples order reduce computational load (MIPS). This means that input exponential filter global energy given
(equation
After that, frequency filtering carried each filter. Prior filtering operation, input sample scaled pointers filter coefficients delays have This done means macro Filter with argument Name, where Name (for example) Dial. First input sample right shifted amount 16-NameShift, i.e. parameter value means shift, means right shift means right shift After scaling, point first filter delay (NameFilter[0]) first filter coefficient (NameFilter[4]). PREG output shift (spm sign extension mode (ssxm). Before call basic filtering routine BIQUAD, current (pointer filter coefficients). BIQUAD performs cascaded filter according equation (N=4). This routine called each filter. fixed-point computation filter coefficients format, input sample filter delays assumed format. output each filter input corresponding exponential filter energy estimation passband. These inputs exponential filters, after frequency filtering, given
(equation
only exponential filter called once every samples, complete routine uses about (M-1)*50 cycles less than computation exponential filters parallel (MIPS memory occupation given more detail later). Finally exponential filters computed decision made whether there enough energy specified passband not. energy estimation different passbands macro called TestOut with argument Name (the same macro Filter) used. output exponential filter calculated specified equation with a=1/64. Then output compared output exponential filter global input:
NameThreshold NameOut TotOut Detection
(equation
global filter output multiplied allow more precision detection threshold. instance, energy passband should more than half global energy detection, then NameThreshold must Increasing threshold means increasing passband detection. case detection, variable CptdFilter each passband. Table gives example masks four different filters.
Programmable Double Biquad Filter Tone Detection Fixed Point DSPs
Table Masks Different Filters
Name Filter1 Filter2 Filter3 Filter4 Value CptdFilter
variable CptdFilter used program upper level timing check. interface between C-programs filter program assembly language will described next section. enhance tone detection some more tests carried out. energy comparison executed global energy does exceed minimum threshold specified variable MinEng. This threshold sets absolute value minimum input signal level that will taken into account. Another point fast detection energy transitions such off/on on/off transitions busy tone. group delay passband filters, comparison energies (equation still result detection even there signal input more. This adaptive threshold test carried detect energy transitions on/off. fact output exponential filter global energy estimation falls below half maximum value determined during detection phase then decision result non-detection:
TotOut TotMax Detection
(equation
different steps involved detection phase summarized flow chart below. decision stage executed separately each filter.
Programmable Double Biquad Filter Tone Detection Fixed Point DSPs
Figure Flow Chart Decision Stage Detection Process
Decision Stage
Global energy min. thres.
Global energy 0.5* max. global energy
Inband energy Threshold global energy
mask variable Detect Reset filter delays, exponential filter output max. energy
Global energy max. energy Max. global energy
Reset mask variables Detect CptdFilter
mask variables Detect CptdFilter
Return calling function
Summary Programmable Parameters
parameters which user programmable filter coefficients, scale factor, detection threshold minimum energy threshold.
Filter Coefficients
filter coefficients have generated design tool based cascade structure shown Figure (filter order N=4). next step consists quantizing filter coefficients obtain format. This means that coefficients have multiplied addition that, coefficients ai1, have multiplied Then these values have defined file Filters.h. steps generate quantized filter coefficients illustrated Each filter contains elements, four filter delays filter coefficients. Initialization carried described previously.
Programmable Double Biquad Filter Tone Detection Fixed Point DSPs
Scale Factor
scale factor specifies shift that applied input sample before bandpass filtering. This shift file Filters.h means constant called NameScale. scale factor value less. 16-Scale Factor specifies right shift applied input sample before frequency filtering stage. Possible values scale factor corresponding right shift given Table
Table Scale Factors Corresponding Right Shift Input Sample
Scale Factor right shift
Common values scale factor depending amplification input stage. important saturate frequency exponential filters.
Detection Threshold
detection threshold specifies minimum amount energy that present passband corresponding filter comparison global energy. other words inband energy must greater than specified fraction global energy, typically:
InbandEnergy GlobalEnergy
(equation
where energy fraction equals 0.5. comparison carried after exponential filters given equation minimum fraction energy detection then given divided detection threshold. Different values detection threshold corresponding energy fraction given Table
Table Detection Thresholds Corresponding Energy Fraction
Detection Threshold Energy Fraction
smaller energy fraction required detection larger passband corresponding filter. common value detection threshold
Minimum Energy Threshold
minimum energy threshold specifies minimum absolute signal level that detected. minimum signal level typically takes values between dBm. minimum energy threshold hardware dependent, signal level input converter determined analog amplification stage. Consequently determined experimentally. order minimum energy threshold, variable TotOut monitored while injecting signal input. TotOut contains output exponential filter global energy that will compared minimum energy threshold during decision stage. continuous signal minimum signal level that shall detected injected input, TotOut will take value that equals minimum energy threshold. value obtained this then Filters.h copied variable MinEng during initialization phase.
Programmable Double Biquad Filter Tone Detection Fixed Point DSPs
Interface Between High Level Programs Filter Program
this section interface between program executing main task filter program executed sample interrupt will described. detection result tone detection procedure used high level application order carry timing check. this purpose variables needed, which have referenced external variables program: CptdFilter Tim0. CptdFilter contains mask corresponding filter case detection (Table zero case detection. Tim0 timer that incremented sample interrupt. maximum value 7fff hex, which corresponds seconds kHz. filters used program have initialized with parameter values specified file Filters.h. This done function Init-() that found file initFilt.c (where stands filter name). routine InitTot() called order initialize exponential filter global energy estimation. example program which carries cadence check busy tone given Figure program main() calls function dialing which include dial tone detection. After that routine CadenceCheck called, which checks presence tone passband filter Dial (bit mask CptdFilter) then carries timing check concerning on/off sequence signal shown Figure
Figure Cadence Check Busy Tone Detection
Busy tone Min. max. timing
Busy tone off: Min. max. timing Tolerance concerning timing taken into account program constant values BusyMin BusyMax which correspond nominal timing nominal timing +x%, respectively. function CadenceCheck indicates busy tone detection return value
Programmable Double Biquad Filter Tone Detection Fixed Point DSPs
Processor Resources Used Filter Programs
Table summarizes memory occupation (RAM ROM) well computational load (MIPS) utilized filter functions contained file biquad.asm.
Table Processor Resources Required Tone Detection Module
words words (biquad.asm) words (initFilt.c) MIPS kHz) kHz)
space reserved filter variables file biquad.asm. section containing these variables called Filter. linker command file this section block contained within memory page (128 words). combination with V22bis modem TMS320C2xx filters executed sampling rate kHz.
Reference
DFDP3/plus Digital Filter Design Package Instruction Manual; Atlanta Signal Processing Inc., 1991
Appendix Source Code
FILE: BIQUAD.ASM
File: BIQUAD.ASM Author: Katrin Matthes Description: Implementation programmable double biquad filter with detection stage (exponential filters) NUMFILTER .set example implementation: Dial/Busy tone tone detector .def CPTD .def .def _CptdFilter .ref FromAD,ForDA .def _TotIn, _TotOut .def _MinEng .def _FiltFunc .def _InitFiltFunc .def NUMFILTER .def
Programmable Double Biquad Filter Tone Detection Fixed Point DSPs
.def .def
.elseif NUMFILTER .elseif NUMFILTER .endif .mmregs
BIQUAD INDEXED y(n)=B0x(n)+d1(n-1) d1(n)=B1x(n)-A1y(n)+d2(n-1) d2(n)=B2x(n)-A2y(n) INPUT: contains scaledinput sample DNM1 PM=1 (<<1) SSXM OUTPUT DNM1 MODIFIED AR0, cycles DATA ORGANIZATION: ;D1NM1 .BSS ;D2NM1 .BSS .BSS .BSS .BSS .BSS .BSS BIQUAD filter coefficients SECOND-ORDER FILTER SECTION #TMP ;GET SCALED INPUT *+,ar0 INPUT *+,15,ar1 ;AC= MPYA *+,ar0 ;AC= (B0* INPUT) INPUT #Output SACH Output,1 ;Save OUTPUT Output ;AC= INPUT *-,15,ar1 ;AC= (B1* INPUT) OUTPUT APAC *+,ar0 ;AC= (B1*INPUT)+(A1*OUTPUT) OUTPUT SACH *+,1,ar1 ;Save #TMP
Programmable Double Biquad Filter Tone Detection Fixed Point DSPs
APAC SACH sacl MPYA SACH APAC SACH APAC SACH
*+,ar0
;AC= OUTPUT INPUT ;AC= *INPUT)+(A2 OUTPUT) *+,1,ar1 ;Save
#Output Output #TMP *+,ar0 *+,15,ar1 *+,ar0 #Output Output,1 Output *-,15,ar1 *+,ar0 *+,1,ar1 #TMP *+,ar0 *+,1,ar1 ;GET ;AC= ;AC= SCALED INPUT INPUT +(B0* INPUT) INPUT
;Save OUTPUT ;AC= INPUT ;AC= +(B1* INPUT) OUTPUT ;AC= +(B1*INPUT)+(A1*OUTPUT) OUTPUT ;Save ;AC= OUTPUT INPUT ;AC= *INPUT) OUTPUT) ;Save
macro filter cycles ;-Filter .macro Name .NEWBLOCK #_:Name:Shift _:Name:Shift LDPK #FromAD LACT FromAD ;load input sample with specified ;shift LDPK #TMP MULTIPLY INPUT GAIN SACH POINTERS LARK CALL
AR0,#_:Name:Filter *,AR0 d1(n-1) AR1,#4 *,AR1 *0+,AR1 BIQUAD
Programmable Double Biquad Filter Tone Detection Fixed Point DSPs
sacl sacl .endm
#Output Output
accumulate absolute value input samples
#_:Name:In _:Name:In _:Name:In #MaxVal #MaxVal _:Name:In
CPTD FILTER cycles filter cycles (max) ;-CPTD sovm DIAL TONE #FromAD FromAD accumulate absolute value input samples #_TotIn _TotIn sacl _TotIn #MaxVal no_clip #MaxVal sacl _TotIn no_clip Filter Dial NUMFILTER Filter .elseif NUMFILTER Filter Filt4 .elseif NUMFILTER Filter Filt3 .endif cala rovm Inits FiltFunc called InitDial() ;-#_FiltFunc _FiltFunc
Programmable Double Biquad Filter Tone Detection Fixed Point DSPs
_InitFiltFunc sacl sacl sacl
#_FiltFunc #TotExp _FiltFunc TotMax Detect
Macro calculation exponential filter based ABS(input sample) Comparison global output filtered (biquad) output (global <=factor filtered) then DETECTION This comparison carried minimum global energy below threshold MinEng energy after filtering below noise threshold filter global energy decreases 0.5* Max, indicating transition on/off cycles ;-TestOut .macro Name .newblock #_:Name:Out zalr _:Name:Out ROUNDING _:Name:In,16-6 1/64 _:Name:Out,16-6 SACH _:Name:Out blez blez blez _TotOut _MinEng _TotOut,1 TotMax _:Name:Out #:Name:Min check min. thres.
TotOut 0.5*TotMax detection: ON/OFF transition noise filter
_TotOut,4 Totout<<4- (factor FilterOut)<<1 _:Name:Threshold Detection test _:Name:Out spac UNDER THRESHOLD Detect #:Name:Mask AR0,#_:Name:Filter
Programmable Double Biquad Filter Tone Detection Fixed Point DSPs
sacl sacl sacl sacl sacl sacl LALK sacl OVER THRESHOLD blez sacl LALK sacl SACL sacl .endm
*,ar0 _:Name:Out TotMax clear clear clear clear D11(N-1) D12(N-1) D21(N-1) D22(N-1)
#~:Name:Mask Detect Detect #_CptdFilter _CptdFilter
_TotOut TotMax _TotOut TotMax
look maximum
#:Name:Mask Detect Detect _CptdFilter _CptdFilter _:Name:In
exponential filter global signal ;-TotExp #DialExp sacl _FiltFunc zalr _TotOut ROUNDING #_TotIn _TotIn,16-6 1/64 LDPK #_TotOut _TotOut,16-6 SACH _TotOut #_TotIn sacl _TotIn exponential filter signal after Dialfilter ;-DialExp NUMFILTER #FaxExp .else
Programmable Double Biquad Filter Tone Detection Fixed Point DSPs
#TotExp .endif sacl _FiltFunc TestOut Dial exponential filter signal after Faxfilter ;-.if NUMFILTER FaxExp NUMFILTER #Filt3Exp .else #TotExp .endif sacl _FiltFunc TestOut .endif exponential filter signal after Filt3 filter ;-.if NUMFILTER Filt3Exp NUMFILTER #Filt4Exp .else #TotExp .endif sacl _FiltFunc TestOut Filt3 .endif
exponential filter signal after Filt4 filter ;-.if NUMFILTER Filt4Exp #TotExp sacl _FiltFunc TestOut Filt4 .endif
_CptdFilter .usect "Filter",1 Output .usect "Filter",1 _TotIn .usect "Filter",1 _TotOut .usect "Filter",1 _DialFilter .usect "Filter",14 _DialIn .usect "Filter",1 _DialOut .usect "Filter",1 _DialShift .usect "Filter",1 _DialThreshold .usect "Filter",1
Programmable Double Biquad Filter Tone Detection Fixed Point DSPs
NUMFILTER _FaxFilter .usect "Filter",14 _FaxIn .usect "Filter",1 _FaxOut .usect "Filter",1 _FaxShift .usect "Filter",1 _FaxThreshold .usect "Filter",1 .elseif NUMFILTER _Filt3Filter .usect "Filter",14 _Filt3In .usect "Filter",1 _Filt3Out .usect "Filter",1 _Filt3Shift .usect "Filter",1 _Filt3Threshold .usect "Filter",1 .elseif NUMFILTER _Filt4Filter .usect "Filter",14 _Filt4In .usect "Filter",1 _Filt4Out .usect "Filter",1 _Filt4Shift .usect "Filter",1 _Filt4Threshold .usect "Filter",1 .endif _MinEng .usect "Filter",1 _FiltFunc .usect "Filter",1 Detect .usect "Filter",1 TotMax .usect "Filter",1 .usect "Filter",1 MaxVal DialMin FaxMin Filt3Min Filt4Min DialMask FaxMask Filt3Mask Filt4Mask .set .set .set .set .set .set .set .set .set 7fffh 0001h 0002h 0004h 0008h
FILE: INITFILT.C
File: INITFILT.C Author: Katrin Matthes /*Routine initializes CPTD Filters double biquad Memory Organization: NameFilter: D11(N-1) D12(N-1) D21(N-1) D22(N-1)
Programmable Double Biquad Filter Tone Detection Fixed Point DSPs
#include "Filters.h" extern DialFilter[14]; extern DialThreshold; extern DialIn, DialOut, TotIn, TotOut, DialShift; NUMFILTER extern FaxFilter[14]; extern FaxThreshold; extern FaxIn, FaxOut, FaxShift; #elif NUMFILTER extern Filt3Filter[14]; extern Filt3Threshold; extern Filt3In, Filt3Out, Filt3Shift; #elif NUMFILTER extern Filt4Filter[14]; extern Filt4Threshold; extern Filt4In, Filt4Out, Filt4Shift; #endif extern MinEng; InitFiltFunc(void);
void InitTot(void) MinEng=MinThres; TotIn=0; TotOut=0; InitFiltFunc();
void InitDial(void) DialFilter[0]=0; DialFilter[1]=0; DialFilter[2]=0; DialFilter[3]=0; DialFilter[4]=Dial1_B0; DialFilter[5]=Dial1_B1; DialFilter[6]=Dial1_A1; DialFilter[7]=Dial1_A2; DialFilter[8]=Dial1_B2; DialFilter[9]=Dial2_B0; DialFilter[10]=Dial2_B1; DialFilter[11]=Dial2_A1; DialFilter[12]=Dial2_A2; DialFilter[13]=Dial2_B2; DialThreshold=DialThres; DialIn=0; DialOut=0; DialShift=DialScale;
Programmable Double Biquad Filter Tone Detection Fixed Point DSPs
NUMFILTER void InitFax (void) FaxFilter[0]=0; FaxFilter[1]=0; FaxFilter[2]=0; FaxFilter[3]=0; FaxFilter[4]=Fax1_B0; FaxFilter[5]=Fax1_B1; FaxFilter[6]=Fax1_A1; FaxFilter[7]=Fax1_A2; FaxFilter[8]=Fax1_B2; FaxFilter[9]=Fax2_B0; FaxFilter[10]=Fax2_B1; FaxFilter[11]=Fax2_A1; FaxFilter[12]=Fax2_A2; FaxFilter[13]=Fax2_B2; FaxThreshold=FaxThres; FaxIn=0; FaxOut=0; FaxShift=FaxScale; #elif NUMFILTER void InitFilt3 (void) Filt3Filter[0]=0; Filt3Filter[1]=0; Filt3Filter[2]=0; Filt3Filter[3]=0; Filt3Filter[4]=Filt3_1_B0; Filt3Filter[5]=Filt3_1_B1; Filt3Filter[6]=Filt3_1_A1; Filt3Filter[7]=Filt3_1_A2; Filt3Filter[8]=Filt3_1_B2; Filt3Filter[9]=Filt3_2_B0; Filt3Filter[10]=Filt3_2_B1; Filt3Filter[11]=Filt3_2_A1; Filt3Filter[12]=Filt3_2_A2; Filt3Filter[13]=Filt3_2_B2; Filt3Threshold=Filt3Thres; Filt3In=0; Filt3Out=0; Filt3Shift=Filt3Scale; #elif NUMFILTER void InitFilt4 (void) Filt4Filter[0]=0; Filt4Filter[1]=0;
Programmable Double Biquad Filter Tone Detection Fixed Point DSPs
Filt4Filter[2]=0; Filt4Filter[3]=0; Filt4Filter[4]=Filt4_1_B0; Filt4Filter[5]=Filt4_1_B1; Filt4Filter[6]=Filt4_1_A1; Filt4Filter[7]=Filt4_1_A2; Filt4Filter[8]=Filt4_1_B2; Filt4Filter[9]=Filt4_2_B0; Filt4Filter[10]=Filt4_2_B1; Filt4Filter[11]=Filt4_2_A1; Filt4Filter[12]=Filt4_2_A2; Filt4Filter[13]=Filt4_2_B2; Filt4Threshold=Filt4Thres; Filt4In=0; Filt4Out=0; Filt4Shift=Filt4Scale; #endif
FILE: FILTERS.H
File: FILTERS.H Author: Katrin Matthes Include file containing filter coefficients double biquad filters #define NUMFILTER define number filters executed parallel Dial Filter*/ coefficients Coefficients biquad #define Dial1_B0 #define Dial1_B1 -914 #define Dial1_B2 #define Dial1_A1 30507 #define Dial1_A2 -16092 Coefficients biquad #define Dial2_B0 4602 #define Dial2_B1 -9029 #define Dial2_B2 4602 #define Dial2_A1 30881 #define Dial2_A2 16118 #define DialScale /*input sample
threshold dial tone detection #define DialThres 0x28 0x31
Filter 1100
Programmable Double Biquad Filter Tone Detection Fixed Point DSPs
Coefficients biquad #define Fax1_B0 1209 #define Fax1_B1 -999 #define Fax1_B2 1209 #define Fax1_A1 20049 #define Fax1_A2 -15773 Coefficients biquad #define Fax2_B0 4616 #define Fax2_B1 -7426 #define Fax2_B2 4616 #define Fax2_A1 21726 #define Fax2_A2 -15806 #define FaxScale input sample
threshold answer tone detection #define FaxThres 0x25 /*0x2a*/
Filt3 Filter Coefficients biquad #define Filt3_1_B0 #define Filt3_1_B1 #define Filt3_1_B2 #define Filt3_1_A1 #define Filt3_1_A2 Coefficients biquad #define Filt3_2_B0 #define Filt3_2_B1 #define Filt3_2_B2 #define Filt3_2_A1 #define Filt3_2_A2 #define Filt3Scale input sample
threshold Filt3 detection #define Filt3Thres 0x18 /*0x38*/
Filt4 Filter Coefficients biquad #define Filt4_1_B0 #define Filt4_1_B1 #define Filt4_1_B2 #define Filt4_1_A1 #define Filt4_1_A2 Coefficients biquad #define Filt4_2_B0 #define Filt4_2_B1 #define Filt4_2_B2 #define Filt4_2_A1 #define Filt4_2_A2 #define Filt4Scale input sample
threshold Filt4 detection #define Filt4Thres 0x20
/*0x38*/
Programmable Double Biquad Filter Tone Detection Fixed Point DSPs
#define MinThres 0x110 minimum detection threshold min. max. timing cadence check: busy tone #define BusyMin value 10ms, BusyMax+20ms account filter delay*/ #define BusyMax Masks different Filters*/ #define DialMask 0x0001 #define FaxMask 0x0002 #define Filt3Mask 0x0004 #define Filt4Mask 0x0008 initialization routines implemented filters void InitTot(void); void InitDial(void); NUMFILTER void InitFax(void); #elif NUMFILTER void InitFilt3(void); #elif NUMFILTER void InitFilt4(void); #endif
Appendix Glossary
CPTD Call Progress Tone Detection Infinite Impulse Response
Programmable Double Biquad Filter Tone Detection Fixed Point DSPs
Contact Numbers
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Programmable Double Biquad Filter Tone Detection Fixed Point DSPs
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Programmable Double Biquad Filter Tone Detection Fixed Point DSPs

Digital Signal Processing Solutions Abstract filters describ

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