Measuring a talking quality of a telephone link in a telecommunications nework

• US 20040042617A1
• Filed: 07/30/2003
• Published: 03/04/2004
• Est. Priority Date: 11/09/2000
• Status: Active Grant

• Current Assignee: Koninklijke KPN NV
• Original Assignee: Koninklijke KPN NV
• Inventors: Hekstra, Andries Pieter, Appel, Symon Ronald, Beerends, John Gerard
• Granted Patent: US 7,366,663 B2
• Time in Patent Office: Days
• US Class Current: 379/416
• CPC Class Codes: H04M 3/2236 Quality of speech transmission monitoring
• CPC Class Codes: H04M 3/323 for the arrangements providing the connection (test connection, test call, call simulation)

Abstract

For measuring the influence of noise on the talking quality of a telephone link in a telecommunications network, a talker speech signal (s(t)) and a degraded speech signal (s′(t)) are fed to an objective measurement device (22) for obtaining an output signal (q) representing an estimated value of the talking quality. The degraded signal includes a returned signal (r(t)) originating from the network during transmission of the talker speech signal over the telephone link. The objective measurement carried out by the device is a modified PSQM-like measurement, which is modified as to include a modelling (32b) of masking effects in consequence of noise present in the returned signal. Preferably the modelling includes a noise suppression (42) carried out to a difference signal (D(t, f)) in the loudness density domain using a noise estimation (41).

Claims

1. Method for-measuring a talking quality of a telephone link in a telecommunications network, comprising a main step of subjecting a degraded speech signal s′

(t) with respect to a talker speech signal s(t) to an objective measurement technique (22), and producing a quality signal (q),

wherein the degraded speech signal includes a returned signal r(t), which corresponds to a signal occurring in a return channel of the telephone link during the transmission of the talker speech signal in a forward channel of the telephone link, and said main step includes a step of modelling masking effects in consequence of noise present in the returned signal.

2. Method according to claim 1, wherein the main step comprises:

a first processing step of processing the degraded speech signal (s′

(t)) and generating a first representation signal (R′

(t,f)),

a second processing step of processing the talker speech signal (s(t)) and generating a second representation signal (R(t,f)), and

a combining step of combining the first and second representation signals as to produce the quality signal (q),

the first representation signal (R′

(t,f)) being a representation signal of a signal combination of the talker speech signal and the returned signal, and the combining step including said step of modelling masking effects in consequence of noise present in the returned signal.

3. Method according to claim 2, wherein the combining step includes:

a step of subtracting (32a) the first representation signal from the second representation signal as to produce a difference signal (D(t,f)),

said step of modelling (32b) the masking effects of noise carried out on the difference signal as to produce a modified difference signal, and

a step of integrating (32c) the modified difference signal with respect to frequency and time as to produce the quality signal,

the modelling step including;

a first substep of producing (41) an estimated value (Ne) of the loudness of the noise present in the returned signal, and

a second substep of noise suppression (42;

46) carried out on the difference signal using said produced estimated value (Ne) as to produce the modified difference signal (D′

(t,f)).

4. Method according to claim 3, wherein the second substep of noise suppression includes further substeps of:

deriving (46) from the estimated value (Ne) a loudness criterion (C),

setting (47, 48, 49) distorsions in the loudness (domain) of the difference signal, which do not suffice the criterion, to zero in the loudness (domain) of a thresholded difference signal (D_c(t,f)), and

deriving (50) the modified difference signal (D′

(t,f)) by calculating a distorsion loudness to signal loudness ratio (DSR(t,f)) of the thresholded signal (D_c(t,f)) with respect to a loudness degraded signal (R′

(t)) derived from the first representation signal (R′

(t,f)).

5. Method according to any of the claim 2,-,4, wherein the estimated value of the noise loudness is derived from the first representation signal (R′

(t,f)).

6. Method according to any of the claims 2,-,5, wherein the degraded signal (s′

(t)) is a signal combination of the talker speech signal (s(t)) and the returned signal (r(t)).

7. Method according to any of the claims 2,-,5, wherein the returned signal (r(t)) is used as the degraded signal (s′

(t)) and that an intermediate signal (Ps (f)) obtained during an intermediate stage of the second processing step of processing the reference signal is combined with a corresponding intermediate signal (Ps′

(f)) obtained during a corresponding intermediate stage of the first processing step of processing the degraded signal.

8. Method according to claim 7, wherein the intermediate signal is an Fast Fourier Transform power representation (Ps(f)) of the reference speech signal (s(t)).

9. Method according to any of the claims 1,-,8, wherein the talker speech signal and the returned signal are taken off from an established telephone link.

10. Device for measuring a talking quality of a telephone link in a telecommunications network (10), the device comprising measurement means (22;

31, 36) for subjecting a degraded speech signal s′

(t) with respect to a talker speech signal s(t) to an objective measurement technique, and for producing a quality signal (q),

wherein the degraded speech signal including a returned signal r(t), which corresponds to a signal occurring in a return channel of the telephone link during the transmission of the talker speech signal in a forward channel of the telephone link, and

the measurement means include means (32b) for a modelling of masking effects in consequence of noise present in the returned signal.

11. Device according to claim 10, wherein the device comprises:

first processing means (39) for processing the degraded speech signal (s′

(t)) and generating a first representation signal (R′

(t,f)),

second processing means (38) for processing the talker speech signal (s(t)) and generating a second representation signal (R(t,f)), and

combining means (32) for combining the first and second representation signals as to produce the quality signal (q), the combining means including said means (32b) for modelling the masking effects.

12. Device according to claim 11, wherein the combining means include:

subtracting means (40) for subtracting the first representation signal from the second representation signal as to produce a difference signal (D(t,f)),

said modelling means (41, 42)) for modelling the masking effects carried out on the difference signal as to produce a modified difference signal, and

integrating means (43) for integrating the modified difference signal with respect to frequency and time as to produce the quality signal.

modelling means include;

means (41) for producing an estimated value (Ne) of the loudness of the noise present in the returned signal, and means (42) for carrying out a noise suppression on the difference signal using said produced estimated value (Ne), and for producing the modified difference signal (D′

(t, f))

the first representation signal (R′

(t,f)) being a representation signal of a signal combination of the talker speech signal and the returned signal.

13. Device according to claims 10, 11 or 12, wherein the device includes a signal combinator (24) for combining the talker speech signal (s(t)) and the returned signal (r(t)) as to form the degraded signal (s′

(t)).

14. Device according to claims 10, 11 or 12, wherein the device includes an intermediate signal combination means (55) for combining an intermediate signal (Ps(f)) obtained in an intermediate stage of the second processing means (38) with a corresponding intermediate signal (Ps′

(f)) obtained in a corresponding intermediate stage of the first processing means (39), the degraded signal (s′

(t)) being the returned signal (r(t)).

15. Device according to claim 14, wherein the intermediate signal combination means (55) is included in the first processing means (39) after means (FTT) for performing a Fast Fourier Transform.