CA2118552A1 - Discrete audio frequency tone detection - Google Patents
Discrete audio frequency tone detectionInfo
- Publication number
- CA2118552A1 CA2118552A1 CA 2118552 CA2118552A CA2118552A1 CA 2118552 A1 CA2118552 A1 CA 2118552A1 CA 2118552 CA2118552 CA 2118552 CA 2118552 A CA2118552 A CA 2118552A CA 2118552 A1 CA2118552 A1 CA 2118552A1
- Authority
- CA
- Canada
- Prior art keywords
- sat
- signal
- ignal
- audio frequency
- gain
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Abstract
DISCRETE AUDIO FREQUENCY TONE DETECTION
Abstract of the Disclosure The process of the present invention detects SAT in a received signal. The frequency and amplitude characteristics of the received signal are used to determine if SAT is present.
If the autocorrelation values generate poles in the proper locations, SAT is present.
Abstract of the Disclosure The process of the present invention detects SAT in a received signal. The frequency and amplitude characteristics of the received signal are used to determine if SAT is present.
If the autocorrelation values generate poles in the proper locations, SAT is present.
Description
-1- 21~ ~
DI~ AUDIO ~EQUENCY TONE DETECTION :
S l~he pre~ t inventioD r~ilate~ gen~ly to ~he field of commu~ication~ and par~ arb to to~0 de~o~.
Landline t~lep~ony we~ ~uperi~lsion to de~ect changes in the ~v~tch-hool~ atate caused by t~lB telephoIle user. Mobile telephone supervi~ion abo per~on~ 1;hi~ proce~s but must ~so ensure that adequate RF ~ignal streDg~ and interference protection i8 maintai~ed. ThiB is accomplished by 1 h~
supervi~org audio tone (SAT), a conl;inuou~ out-of-band modulated signal.
T~ree SAT 8ig~1e, are u~ed D3 the UDited State~
cellular system, AMPS. These SAT ~ignal~ are at 5970 Hz, 6000 Hz, and 6030 Hz. Onlg one of the~e ~equen~es iB
DI~ AUDIO ~EQUENCY TONE DETECTION :
S l~he pre~ t inventioD r~ilate~ gen~ly to ~he field of commu~ication~ and par~ arb to to~0 de~o~.
Landline t~lep~ony we~ ~uperi~lsion to de~ect changes in the ~v~tch-hool~ atate caused by t~lB telephoIle user. Mobile telephone supervi~ion abo per~on~ 1;hi~ proce~s but must ~so ensure that adequate RF ~ignal streDg~ and interference protection i8 maintai~ed. ThiB is accomplished by 1 h~
supervi~org audio tone (SAT), a conl;inuou~ out-of-band modulated signal.
T~ree SAT 8ig~1e, are u~ed D3 the UDited State~
cellular system, AMPS. These SAT ~ignal~ are at 5970 Hz, 6000 Hz, and 6030 Hz. Onlg one of the~e ~equen~es iB
2 0 employed at a given cell site.
The SAT operate~ by the bile unit recei~ring the SAT
from the base station and transponding it back to clo~e the loop. l~e base station 1001~B for the return of the ~pecific SAT it ~ent out. If another SAT i~ returned, the c~ll interpret6 thi6 a6 2 5 the call between the mobile and the cell being corrupted by interference.
When a mobile receives a aig~l from the ba~e ~tation, it detect~ whether SAT is pre~ent. Baset on this frequency, the mobile generates its own SAT ~d tran~mits it bac~ to the base 3 0 station. l~ method requires t~e mobile to perform a larg~
number of million in~truclion~ per ~econd (MIPS) in order to detect t~e received SAT and generate the t=itted SAT.
Consumers are demanding smaller cellulsr telephones for greater porhbility. To reduce 1 he l~ize of the telephone~, the 3 5 number of p~tB in t}le ~lephone must be reducet. Thi~ can be accomplished by performing many of the telephone'~
-; : . :;, - . , ~ 2~1~a52 fimclions in a digit~l ~ignal proce~or (DSP3. Thi8, ill effect, r~places a nu~er of integrated ~ts wit~ a ~le DSP
~hat pe~01~18 1~he same fi~clio~ e replaced IC~.
Replacing t~e present SAT detec~o~ and generation 5 circuit~ wi~ a DSP would ~ a ve~y M~S intensive proce~s. Tbi~ would ta~e up time 1he D~P could bs used for other ta~. Addi'donally, the rs~ived 8AT mu~t be adju~ted for ~ di~erences cau~sd by the mobile'~ hard~vare before it ~ :
i~ tra~itted ba~lc to ~he base 8tatiOII. T~i8 would take 1 0 additiol~al 1ime away fiom the DS~. Tnere i~ a re~ulting need for a simple proce~ to detect SAT and adju~t it~ gain.
The procee~ of t;he pre~ent ~ventio~ encompa~ a method for automatically coI~trolling the gain of a t~a~mitted modulation BigIlal. Thi8 control iB ba~ed on a received demodulated ~ignal. The proce~s filter~ the meived signal to produce a Sltered ~ignal. Thi8 filtered 8igllal i8 proces~ed by 2 0 an autocorrelation fi~nction to g~nerate a plurality of autocorrelation values. A desired energy of the filtered signal iB divided by at least one of the autooorrelation values to produce a preliminary ga~ adju8tment ~ al. A filrther gain iB derived from the prel;minar~ g~n adjustment Big 2 5 by tal~g the ~quare root of the prelimi~a~ gain adjusl;ment Bignal. The derived gain i8 scaled in response to lhe gain of the ~nod~ator that modulate~ 1 he trulsmitted signal. This derived gain i~ filtered to produce a filtered gaiD signal. The transmitted signal is generated in response to the filtered gain 3 0 signal and ~e filtered ~ignal.
2 ~ 5 2 ElhOWB a blo~lc diagram of ~he plOCl~ElE of the present in~en~on.
S ~IG. 2 ElhOW8 a block diagram of the &~T detection proCe8a of the pr~sent inventio~
1 0 The prlU:e88 of ~he pre~ent inventio~ enable~ a ~;AT - -detection and automatic ~ control (AGC) p~oce~
~orated into a D~P ~vithout r~quirine a large amount of p~B8~g 1ime. ThiB prOCe811 iB illustrated m 1~e block diagram of EIG. 1.
T'ne proo~ss begins by 1~e received ~ignal being demodulated (102). T'nis de~nodulation prOCeBI~ produces a ~al who~e rm8 value is affiected by both the rece~ed BigII~I
and the gun of the demodulator. Tni~ af~ec~ ia removet by multipl~g (103) the demodulated ~ignal by the value N. N is 2 0 chosen BO that for a known received sigDal, the signal at the input to the bandpa~s filter (104) is Icnown; i.e., N is adjusted for each radiotelepho~e to remo~e the effects of demodulator gain varianc~ f~om radiot~lephone to radiotelephone.
To illustrab this adjustment, one embodiment of the 2 5 pre~ent invention might ha~re a received Bignal with an appronmate 2.0 kHz deviation at a 6.0 kHz rate. The actual received ~ignal may be other than e~ y 2.0 kHz de~Tiation, but the trsnsmitted signal needs to be e~ y, or substantially close to a 2.0 k~z de~iatio~ independent of the esact received 3 0 signal deviation. The tran~ponded rece*ed signal, therefore, needs to have its gain adju~ted as the demodulated rece*et signal varies.
For a received signal with a 2.0 kHz devia~o~ at a 6.0 kHz rate, a demodulated signal, a(t) is producet. This 9ignal 3 5 i8 1hen sampled and ga~ adju~ted to produce a diacrete signal, s(n), with an rms v~lue D. ~(n) is then filtered by a '.'`"'`"', '", ,, ~
' "' '~
2 ~ 2 narrowband bandpa~ filter tlO4) ~harac~rizsd by tran~fer fmlction h(n) wh4~e output, ytn) ha~ value E. The BPF
(104) remOVeB e~h and noi~e ~o 1~at ytn) i~ a fairly c3o~e repre~entation of SAT.
S y(n) i~ input to an autocorr~lation fi~ction calculator (106)that generates outpub r~(O), rs(1), and r~(2). Th~se ou~put ralues are the e~rg~r of each sample of the sampled Bignal, ~(n). r~(O) for an input sine ~vave of nns value E ha~ value 132.
The radiotelephone's t~tbr al~o has a variance iiom radiot~lephone to radiote~ephone ~br effective tran~it deviation. To produoe a }nown de~atioll, the modulation level must be adjusted to compensate for t~i~ ~uiance. T'ni~ is done by adjusting the value of the constant L for ea~ individual radiotelephone .
The proeess of the present ill~ention performs SAT
modulation gain adjustment by u~g the E2 value to derive a gain adjus~ent for the output ~ignal pnor to its pas6age to - -; -~
the tran~itter. Tbis adjw~ent is performed by t}le proces~
ofthe present invention by sc~ling the signal, ~(n) to produce a 2 0 signal of amplitute G. An input sinusoidal signal of rm~
~alue G is required at the input of the t itter to produce a 2.0 kHz denated sigDal at the tran~itter output.
G is determined by the follo~ving equation~
2 5 G = L
A2 :.
where the values for - 2Dl' and L are cllosen ~o that for an autocorrelation output of E2, a ~ignal of rms value G iB
generated if y(n) is at the correct f~equen~y and v.1ithin an 3 0 amplitud~ windo~r, as determined by ~he SAT detector.
The output of the abo~e op~ration is input to a low pallB
filbr (LPF) (106). T~e LPF (106) reduoe~ 1 he variance of the gun ad,justment siFnal to keep the tran~mitted aigllal from e~periencing large amplitude cha~ges.
~ . ~ . , ... . . . . .. ,, . .. ~, .. .... ... ... ... ..... . ..... ..... .... . . . .. . .. .
.' ., ' ' " ' ' ' ~ . . ' . , . ' :
2~8.S5~
T'ne output of th~ LPF (106) is one ~ut to a ~wit~hing opera~n (101). If S~T i~ det~d b~r th0 SAT debctor (110), the ou~ut ofthe LPF (106) i~ ub0equeQt operation~. If 8AT i~ t detected, the gain of the traDsmitted sig~ et to 5 zero.
Tn~ SAT detector (110) of the pr~t inv~on detern~ines the pre~ence of t~ ~T ~ignal by the amplitude and i~uenc~ ~eri~ics of the received Bignal. To aooompli~h thi~, ~e proce~s i~lustrated ~ ~IG. a iB u~ed.
Tkis proceas beg~ns by the autocorre~ation vs~ue~ ~om 1 he autocorrel~tion calculator being ~put to the SAT detector.
Using the Le~insoll-Durbin ~ve proce~s, direct form ~efficie~ts are generated from 1~ autoGorrelation ~alues.
The pole loca~ of the autocorrelation value~ are then 1 5 ge~lerated by ~putting the ~:oefficients into a quadratic equation. l~he f~equency of 1he receqved signal i~
determined bg these pole location~. T'ne ~mplitude ~haracteristic is terived na r,(0) and and compared ~ith a possibly variable thre~hold. If E2, as mea~ured by r~(0) is 2 0 abo~e the threshold, the received SAT is determined to have sufficient amplitude to be detected, if 1 he f~equency, as determined by pole locations, i8 acceptable.
The SAT frequency detection process can be represented mathematically as follows. The z - traDsform of a ~ine wave is: 5 sin(~ => z2 2zco~ T) + 1 where: ~ = 2~o (fo S z~ d T = sampling rate.
Tbi8 CaD alBO bewritten a~
~ :
. ( ) z~ DT) 1- 2z ~(~DT)~Z'2 The equation for a second order linear tim~-invariant discrete-time ~ystem iB:
. .
~ -6- 2118~
H(z)' aO al~l ab~2 Equating ~e coefficienb of 1ihe ~ fimction wit~ 1 hat of 5 ~I(z) give~:
bo=O aO=l q = 2cos(a~
b2 = o a2 = -l '' ~ince the ~equenc~ o 1 he rec~ved BigDal iB wanted, the ~ of a ~ oidal ~al can be esplit:i1 Iy repre~ented :
by 1he de~ominator of H(z). The numerator of H(z) ~res oDly gain infonnatio~L U~ t~e ~a~c equation to find the :
pole locatioDs in the z-doma-n give8: ~
a2(1) ~ (1)+4a2(0)ag(2) ~ ~:
z=
The frequency of the recei~ed ~inusoid~l ~ignal i6: :~
o=tan~ (1)+2~1a)2()a2( )3~
The denominator coefficients of the ~econd-order linear time-invanant di~crete-time ~y~ be ea~ily detennined ~ -2 5 by u~ he Lenn~on-Durbin recur~ive process. The Lenn~on-Durbin recur~ive proce~ for detormining 1 he direct form coefficient~ iB a~ foillow~, where r~m) i~ ~he unbia6ed edimate of the true autocorr~ation.
N-Y-l 3 r~S(m) = N - M n~O n + ~ X~[n]
where: X(n) = discrete data ~ample, -. ,;~. ;. . i .. .~ . .. . .. .;. . . . .. .. . .
~~ 7 2~1 8~52 . :
N = anal~ 1 Now r,stO), r~(l), alld r"(2), the autooorr~ation ~alue~
fra~ the autocorrelation calculator, are wed to calculat~ the ~ form coefficients.
~0)= 1 a2(1) = al(l) + r2 al(l) a,(2) =r2 1 0 where a~(l) = r~ = r,~O) l~s(2) ~ al(l) r~(l)] r~
r2= ~(U-~tO) :
r~2~r~,(0) . r~(1) 1 -~
r2 r~"(l) - r~(O) 1 5 ' ~, :
a2(o) S 1 a2(1) = r~(V - [(r (1) r~((O3)(r~(l)) + r (0))3 2 r~(2)r~u(0) - ~(1) a2( ) = ~,~(1) - ~() a2(1)=r~(l ~( ) ~( )]
If the frequenc~ of the ~ignal iB determ~et to be eit her ~970 Hz i lO Hz, 6000 Hz i lO Hz, or 60~0 Hz i lO Hz, &~T i~
2 5 present in the receiYed Etignal. If SAT is pre~ent, ~he SAT :
detector (110) enable~ t~e s~itchi~ nction (101) to allow the gain adjusted ~ignal t~rough If SAT is not present, the SAT
detector (110) enable~ 1he swits l~g function (101) to output a mute control (120) ~ignal.
' ' ;,':
.,
The SAT operate~ by the bile unit recei~ring the SAT
from the base station and transponding it back to clo~e the loop. l~e base station 1001~B for the return of the ~pecific SAT it ~ent out. If another SAT i~ returned, the c~ll interpret6 thi6 a6 2 5 the call between the mobile and the cell being corrupted by interference.
When a mobile receives a aig~l from the ba~e ~tation, it detect~ whether SAT is pre~ent. Baset on this frequency, the mobile generates its own SAT ~d tran~mits it bac~ to the base 3 0 station. l~ method requires t~e mobile to perform a larg~
number of million in~truclion~ per ~econd (MIPS) in order to detect t~e received SAT and generate the t=itted SAT.
Consumers are demanding smaller cellulsr telephones for greater porhbility. To reduce 1 he l~ize of the telephone~, the 3 5 number of p~tB in t}le ~lephone must be reducet. Thi~ can be accomplished by performing many of the telephone'~
-; : . :;, - . , ~ 2~1~a52 fimclions in a digit~l ~ignal proce~or (DSP3. Thi8, ill effect, r~places a nu~er of integrated ~ts wit~ a ~le DSP
~hat pe~01~18 1~he same fi~clio~ e replaced IC~.
Replacing t~e present SAT detec~o~ and generation 5 circuit~ wi~ a DSP would ~ a ve~y M~S intensive proce~s. Tbi~ would ta~e up time 1he D~P could bs used for other ta~. Addi'donally, the rs~ived 8AT mu~t be adju~ted for ~ di~erences cau~sd by the mobile'~ hard~vare before it ~ :
i~ tra~itted ba~lc to ~he base 8tatiOII. T~i8 would take 1 0 additiol~al 1ime away fiom the DS~. Tnere i~ a re~ulting need for a simple proce~ to detect SAT and adju~t it~ gain.
The procee~ of t;he pre~ent ~ventio~ encompa~ a method for automatically coI~trolling the gain of a t~a~mitted modulation BigIlal. Thi8 control iB ba~ed on a received demodulated ~ignal. The proce~s filter~ the meived signal to produce a Sltered ~ignal. Thi8 filtered 8igllal i8 proces~ed by 2 0 an autocorrelation fi~nction to g~nerate a plurality of autocorrelation values. A desired energy of the filtered signal iB divided by at least one of the autooorrelation values to produce a preliminary ga~ adju8tment ~ al. A filrther gain iB derived from the prel;minar~ g~n adjustment Big 2 5 by tal~g the ~quare root of the prelimi~a~ gain adjusl;ment Bignal. The derived gain i8 scaled in response to lhe gain of the ~nod~ator that modulate~ 1 he trulsmitted signal. This derived gain i~ filtered to produce a filtered gaiD signal. The transmitted signal is generated in response to the filtered gain 3 0 signal and ~e filtered ~ignal.
2 ~ 5 2 ElhOWB a blo~lc diagram of ~he plOCl~ElE of the present in~en~on.
S ~IG. 2 ElhOW8 a block diagram of the &~T detection proCe8a of the pr~sent inventio~
1 0 The prlU:e88 of ~he pre~ent inventio~ enable~ a ~;AT - -detection and automatic ~ control (AGC) p~oce~
~orated into a D~P ~vithout r~quirine a large amount of p~B8~g 1ime. ThiB prOCe811 iB illustrated m 1~e block diagram of EIG. 1.
T'ne proo~ss begins by 1~e received ~ignal being demodulated (102). T'nis de~nodulation prOCeBI~ produces a ~al who~e rm8 value is affiected by both the rece~ed BigII~I
and the gun of the demodulator. Tni~ af~ec~ ia removet by multipl~g (103) the demodulated ~ignal by the value N. N is 2 0 chosen BO that for a known received sigDal, the signal at the input to the bandpa~s filter (104) is Icnown; i.e., N is adjusted for each radiotelepho~e to remo~e the effects of demodulator gain varianc~ f~om radiot~lephone to radiotelephone.
To illustrab this adjustment, one embodiment of the 2 5 pre~ent invention might ha~re a received Bignal with an appronmate 2.0 kHz deviation at a 6.0 kHz rate. The actual received ~ignal may be other than e~ y 2.0 kHz de~Tiation, but the trsnsmitted signal needs to be e~ y, or substantially close to a 2.0 k~z de~iatio~ independent of the esact received 3 0 signal deviation. The tran~ponded rece*ed signal, therefore, needs to have its gain adju~ted as the demodulated rece*et signal varies.
For a received signal with a 2.0 kHz devia~o~ at a 6.0 kHz rate, a demodulated signal, a(t) is producet. This 9ignal 3 5 i8 1hen sampled and ga~ adju~ted to produce a diacrete signal, s(n), with an rms v~lue D. ~(n) is then filtered by a '.'`"'`"', '", ,, ~
' "' '~
2 ~ 2 narrowband bandpa~ filter tlO4) ~harac~rizsd by tran~fer fmlction h(n) wh4~e output, ytn) ha~ value E. The BPF
(104) remOVeB e~h and noi~e ~o 1~at ytn) i~ a fairly c3o~e repre~entation of SAT.
S y(n) i~ input to an autocorr~lation fi~ction calculator (106)that generates outpub r~(O), rs(1), and r~(2). Th~se ou~put ralues are the e~rg~r of each sample of the sampled Bignal, ~(n). r~(O) for an input sine ~vave of nns value E ha~ value 132.
The radiotelephone's t~tbr al~o has a variance iiom radiot~lephone to radiote~ephone ~br effective tran~it deviation. To produoe a }nown de~atioll, the modulation level must be adjusted to compensate for t~i~ ~uiance. T'ni~ is done by adjusting the value of the constant L for ea~ individual radiotelephone .
The proeess of the present ill~ention performs SAT
modulation gain adjustment by u~g the E2 value to derive a gain adjus~ent for the output ~ignal pnor to its pas6age to - -; -~
the tran~itter. Tbis adjw~ent is performed by t}le proces~
ofthe present invention by sc~ling the signal, ~(n) to produce a 2 0 signal of amplitute G. An input sinusoidal signal of rm~
~alue G is required at the input of the t itter to produce a 2.0 kHz denated sigDal at the tran~itter output.
G is determined by the follo~ving equation~
2 5 G = L
A2 :.
where the values for - 2Dl' and L are cllosen ~o that for an autocorrelation output of E2, a ~ignal of rms value G iB
generated if y(n) is at the correct f~equen~y and v.1ithin an 3 0 amplitud~ windo~r, as determined by ~he SAT detector.
The output of the abo~e op~ration is input to a low pallB
filbr (LPF) (106). T~e LPF (106) reduoe~ 1 he variance of the gun ad,justment siFnal to keep the tran~mitted aigllal from e~periencing large amplitude cha~ges.
~ . ~ . , ... . . . . .. ,, . .. ~, .. .... ... ... ... ..... . ..... ..... .... . . . .. . .. .
.' ., ' ' " ' ' ' ~ . . ' . , . ' :
2~8.S5~
T'ne output of th~ LPF (106) is one ~ut to a ~wit~hing opera~n (101). If S~T i~ det~d b~r th0 SAT debctor (110), the ou~ut ofthe LPF (106) i~ ub0equeQt operation~. If 8AT i~ t detected, the gain of the traDsmitted sig~ et to 5 zero.
Tn~ SAT detector (110) of the pr~t inv~on detern~ines the pre~ence of t~ ~T ~ignal by the amplitude and i~uenc~ ~eri~ics of the received Bignal. To aooompli~h thi~, ~e proce~s i~lustrated ~ ~IG. a iB u~ed.
Tkis proceas beg~ns by the autocorre~ation vs~ue~ ~om 1 he autocorrel~tion calculator being ~put to the SAT detector.
Using the Le~insoll-Durbin ~ve proce~s, direct form ~efficie~ts are generated from 1~ autoGorrelation ~alues.
The pole loca~ of the autocorrelation value~ are then 1 5 ge~lerated by ~putting the ~:oefficients into a quadratic equation. l~he f~equency of 1he receqved signal i~
determined bg these pole location~. T'ne ~mplitude ~haracteristic is terived na r,(0) and and compared ~ith a possibly variable thre~hold. If E2, as mea~ured by r~(0) is 2 0 abo~e the threshold, the received SAT is determined to have sufficient amplitude to be detected, if 1 he f~equency, as determined by pole locations, i8 acceptable.
The SAT frequency detection process can be represented mathematically as follows. The z - traDsform of a ~ine wave is: 5 sin(~ => z2 2zco~ T) + 1 where: ~ = 2~o (fo S z~ d T = sampling rate.
Tbi8 CaD alBO bewritten a~
~ :
. ( ) z~ DT) 1- 2z ~(~DT)~Z'2 The equation for a second order linear tim~-invariant discrete-time ~ystem iB:
. .
~ -6- 2118~
H(z)' aO al~l ab~2 Equating ~e coefficienb of 1ihe ~ fimction wit~ 1 hat of 5 ~I(z) give~:
bo=O aO=l q = 2cos(a~
b2 = o a2 = -l '' ~ince the ~equenc~ o 1 he rec~ved BigDal iB wanted, the ~ of a ~ oidal ~al can be esplit:i1 Iy repre~ented :
by 1he de~ominator of H(z). The numerator of H(z) ~res oDly gain infonnatio~L U~ t~e ~a~c equation to find the :
pole locatioDs in the z-doma-n give8: ~
a2(1) ~ (1)+4a2(0)ag(2) ~ ~:
z=
The frequency of the recei~ed ~inusoid~l ~ignal i6: :~
o=tan~ (1)+2~1a)2()a2( )3~
The denominator coefficients of the ~econd-order linear time-invanant di~crete-time ~y~ be ea~ily detennined ~ -2 5 by u~ he Lenn~on-Durbin recur~ive process. The Lenn~on-Durbin recur~ive proce~ for detormining 1 he direct form coefficient~ iB a~ foillow~, where r~m) i~ ~he unbia6ed edimate of the true autocorr~ation.
N-Y-l 3 r~S(m) = N - M n~O n + ~ X~[n]
where: X(n) = discrete data ~ample, -. ,;~. ;. . i .. .~ . .. . .. .;. . . . .. .. . .
~~ 7 2~1 8~52 . :
N = anal~ 1 Now r,stO), r~(l), alld r"(2), the autooorr~ation ~alue~
fra~ the autocorrelation calculator, are wed to calculat~ the ~ form coefficients.
~0)= 1 a2(1) = al(l) + r2 al(l) a,(2) =r2 1 0 where a~(l) = r~ = r,~O) l~s(2) ~ al(l) r~(l)] r~
r2= ~(U-~tO) :
r~2~r~,(0) . r~(1) 1 -~
r2 r~"(l) - r~(O) 1 5 ' ~, :
a2(o) S 1 a2(1) = r~(V - [(r (1) r~((O3)(r~(l)) + r (0))3 2 r~(2)r~u(0) - ~(1) a2( ) = ~,~(1) - ~() a2(1)=r~(l ~( ) ~( )]
If the frequenc~ of the ~ignal iB determ~et to be eit her ~970 Hz i lO Hz, 6000 Hz i lO Hz, or 60~0 Hz i lO Hz, &~T i~
2 5 present in the receiYed Etignal. If SAT is pre~ent, ~he SAT :
detector (110) enable~ t~e s~itchi~ nction (101) to allow the gain adjusted ~ignal t~rough If SAT is not present, the SAT
detector (110) enable~ 1he swits l~g function (101) to output a mute control (120) ~ignal.
' ' ;,':
.,
Claims
1. A method for detecting a discrete audio frequency tone in a received signal having a frequency, the method comprising the steps of:
generating at least one autocorrelation value;
generating a plurality of direct form coefficients from the at lease one autocorrelation value using Levinson-Durbin Recursive Process;
generating a pole location for each of the at least one autocorrelation values; and determining the frequency of the received signal in response to the pole locations.
generating at least one autocorrelation value;
generating a plurality of direct form coefficients from the at lease one autocorrelation value using Levinson-Durbin Recursive Process;
generating a pole location for each of the at least one autocorrelation values; and determining the frequency of the received signal in response to the pole locations.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US3582993A | 1993-03-23 | 1993-03-23 | |
| US035,829 | 1993-03-23 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2118552A1 true CA2118552A1 (en) | 1994-09-24 |
Family
ID=21885025
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2118552 Abandoned CA2118552A1 (en) | 1993-03-23 | 1994-03-08 | Discrete audio frequency tone detection |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2118552A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1062697C (en) * | 1996-09-05 | 2001-02-28 | 英业达股份有限公司 | Chip for detecting telephone signals with digital signal processor and performing digital communication |
-
1994
- 1994-03-08 CA CA 2118552 patent/CA2118552A1/en not_active Abandoned
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1062697C (en) * | 1996-09-05 | 2001-02-28 | 英业达股份有限公司 | Chip for detecting telephone signals with digital signal processor and performing digital communication |
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Legal Events
| Date | Code | Title | Description |
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| EEER | Examination request | ||
| FZDE | Dead |