Method for using a mobile device equipped with at least two microphones for determining the direction of loudspeakers in a setup of a surround sound system

1. A method for using a smartphone equipped with at least two microphones (m 1 ,m 2 ) for determining the direction of loudspeakers A, in a setup of a surround sound system including N loudspeakers, k=1 . . . N, wherein said direction is expressed by an azimuth angle ϕ k and a polar angle θ k , said method including:

a) setting initial values (ϕ 0 ,θ 0 ) for said azimuth angle ϕ k and said polar angle θ k for loudspeaker l k direction;

b) in a first loop over smartphone position angle α for the determination of one of ϕ k and θ k , and thereafter in a second loop over smartphone position angle α for the determination of the other one of ϕ k and θ k :

c) setting k=1;

d) in a sub-loop over k:

e) in a sub-sub-loop over a rotation angle of said smartphone:

f) causing loudspeaker l k to emit a test signal (s k (t));

g) rotating said smartphone and providing for said smartphone a corresponding measured smartphone rotation angle value α k ,

h) capturing corresponding smartphone microphone signals (y k1 (t), y k2 (t)) from said loudspeaker l k test signal;

i) calculating from said microphone signals a corresponding Time Difference of Arrival value (τ k (α k ));

j) if said Time Difference of Arrival value (τ k (α k )) is not zero or is not smaller than a predetermined threshold value, returning to step f);

k) otherwise, calculating a corresponding azimuth ϕ k or polar θ k , respectively, angle value for the position of loudspeaker l k ;

L) incrementing k by ‘1’;

m) if k≤N, returning to step f);

n) otherwise, checking whether both of ϕ k and θ k have been determined, and if not true, returning to step b);

o) after all positions of said N loudspeakers have been determined, providing a corresponding set of N pairs of azimuth and polar angle values ϕ k and θ k for said loudspeakers l k and for all k;

p) using said corresponding set of pairs of azimuth and polar angle values to accurately calibrate said loudspeakers l k .

2. The method for using a smartphone equipped with at least two microphones (m 1 ,m 2 ), having a known distance (d 12 ) from each other, for determining the direction of loudspeakers l k in a setup of a surround sound system including N loudspeakers, k=1 . . . N, wherein said direction is expressed by an azimuth angle ϕ k and a polar angle θ k , said method including:

a) setting initial values (ϕ 0 ,θ 0 ) for said azimuth angle ϕ k and said polar angle θ k for loudspeaker l k direction;

b) in a first loop over smartphone position angle α for the determination of one of ϕ k and θ k , and thereafter in a second loop over smartphone position angle α for the determination of the other one of ϕ k and θ k :

c) positioning said smartphone at a desired azimuth angle or polar angle;

d) setting k=1;

e) in a sub-loop over k:

f) causing loudspeaker l k to emit a test signal (s k (t));

g) capturing the smartphone microphone signals (y k1 (t), y k2 (t)) from said loudspeaker l k test signal;

h) determining from said captured smartphone microphone signals (y k1 (t), y k2 (t)) a loudspeaker distance difference value (Δ k ) and calculating a corresponding smartphone position angle value (α k ):

i) calculating a corresponding azimuth ϕ k or polar θ k , respectively, angle value for the position of loudspeaker l k ;

j) incrementing k by ‘1’;

k) if k≤N, returning to step f);

I) otherwise, checking whether both of ϕ k and θ k , have been determined, and if not true, returning to step b);

m) after all positions of said N loudspeakers have been determined, providing a corresponding set of N pairs of azimuth and polar angle values ϕ k and θ k for said loudspeakers l k and for all k;

n) using said corresponding set of pairs of azimuth and polar angle values to accurately calibrate said loudspeakers l k .

3. The method according to claim 2 , wherein for determining the distance (d 12 ) between said two microphones (m 1 , m 2 ) the following processing is carried out:

a) selecting one loudspeaker l k of said N loudspeakers;

b) causing loudspeaker l k to emit a test signal (s k (t));

c) capturing the smartphone microphone signals (y k1 (t), y k2 (t)) from said loudspeaker l k test signal;

d) rotating said smartphone and providing for said smartphone a corresponding measured smartphone rotation angle value α k ;

e) calculating a corresponding Time Difference of Arrival value (τ k (α k ));

f) if said Time Difference of Arrival value (τ k (α k )) is not zero or is not smaller than a predetermined threshold value, returning to step b);

g) otherwise, defining an initial direction angle value β=0;

h) rotating said smartphone by an angle β≈π/4 and providing for said smartphone a corresponding measured rotation angle value β;

i) causing loudspeaker l k to emit a test signal (s k (t));

j) capturing the smartphone microphone signals (y k1 (t), y k2 (t)) from said loudspeaker l k test signal;

k) calculating from said smartphone microphone signals (y k1 (t),y k2 (t)) a loudspeaker distance difference value Δ k and a microphone distance value

d

12

=

Δ

k

sin

⁢

⁢

β

.

4. The method according to claim 1 , wherein said smartphone includes an app that controls the processing.

5. The method according to claim 2 , wherein smartphone includes an app that controls the processing.

6. The method according to claim 1 , wherein said smartphone microphone signals are

y k1 ( t )= g ( d k1 ) s k ( t−ΔT k1 )+ n 1 ( t ) and

y k2 ( t )= g ( d k2 ) s k ( t−ΔT k2 )+ n 2 ( t ),

wherein ΔT k1 is the time the sound wave needs for propagating from loudspeaker l k to microphone m 1 and ΔT k2 is the time the sound wave needs for propagating from loudspeaker l k to microphone m 2 , S k (∘) is said test signal, g(d k∘ ) is an attenuation factor which describes the dependence of the amplitude on the distance d k∘ between loudspeaker l k and microphone m 1 or m 2 , and n 1 (t) and n 2 (t) take into account environmental and internal noise of said microphones.

7. The method according to claim 2 , wherein said smartphone microphone signals are

y k1 ( t )= g ( d k1 ) s k ( t−ΔT k1 )+ n 1 ( t ) and

y k2 ( t )= g ( d k2 ) s k ( t−ΔT k2 )+ n 2 ( t ),

wherein ΔT k1 is the time the sound wave needs for propagating from loudspeaker l k to microphone m 1 and ΔT k2 is the time the sound wave needs for propagating from loudspeaker l k to microphone m 2 , S k (∘) is said test signal, g(d k∘ ) is an attenuation factor which describes the dependence of the amplitude on the distance d k∘ between loudspeaker l k and microphone m 1 or m 2 , and n 1 (t) and n 2 (t) take into account environmental and internal noise of said microphones.

8. The method according to claim 6 , wherein said Time Difference of Arrival for loudspeaker l k for said smartphone microphones is defined as τ k =ΔT k1 −τ k2 , which corresponds to the spatial difference Δ k =|d k1 −d k2 |=c|τ k | between said smartphone microphones and said loudspeaker l k with the sound velocity c in air as a scaling factor.

9. The method according to claim 3 , wherein said Time Difference of Arrival for loudspeaker l k for said smartphone microphones is defined as τ k =ΔT k1 −τ k2 , which corresponds to the spatial difference Δ k =|d k1 −d k2 |=c|τ k | between said smartphone microphones and said loudspeaker l k with the sound velocity c in air as a scaling factor.

10. The method according to claim 1 , wherein said Time Difference of Arrival is estimated by using a cross-correlation function

R k (τ)= { y k1 ( t ) y k2 ( t −τ)}=∫ −∞ +∞ Y k1 ( f ) Y k2 *( f )exp 2πifτ df

with y k(1|2) (t) being the signals captured by said smartphone microphones and y k (1l 2 )(f) being their respective Fourier transforms, and wherein the time delay between the microphone signals is obtained by searching the peak in the correlation

τ

k

=

arg

⁢

max

τ

⁢

R

k

⁡

(

τ

)

.

11. The method according to claim 3 , wherein said Time Difference of Arrival is estimated by using a cross-correlation function

R k (τ)= { y k1 ( t ) y k2 ( t −τ)}=∫ −∞ +∞ Y k1 ( f ) Y k2 *( f )exp 2πifτ df

with y k(1|2) (t) being the signals captured by said smartphone microphones and y k(1|2) (f) being their respective Fourier transforms, and wherein the time delay between the microphone signals is obtained by searching the peak in the correlation

τ

k

=

arg

⁢

max

τ

⁢

R

k

⁡

(

τ

)

.

12. The method according to claim 1 , wherein, instead of interactive rotation of said smartphone with respect to each loudspeaker for direction determination, it is assumed that the distances d k1 , d k2 between the microphones of said smartphone and said loudspeaker are much greater than the distance d 12 between the microphones in said smartphone, and the angle α k between the line between both microphones and the direction of said loudspeaker is

α

k

=

arcsin

⁡

(

Δ

k

d

12

)

,

k=1, . . . , N, and wherein, in order to avoid the ambiguity about in which half space a loudspeaker is located, two successive measurements are conducted and in the second measurement said smartphone is rotated by approximately 90° and the determination of the sign of said time delay τ k is used for fixing the direction of said loudspeaker.

13. A computer program product stored on a non-transitory computer readable medium comprising instructions which, when carried out on a mobile device, perform the method according to claim 1 .

14. A computer program product stored on a non-transitory computer readable medium comprising instructions which, when carried out on a mobile device, perform the method according to claim 2 .

15. A measurement device for determining the direction of loudspeakers l k in a setup of a surround sound system including N loudspeakers, k=1 . . . N, adapted to cooperate with a smartphone equipped with at least two microphones (m 1 ,m 2 ), wherein said direction is expressed by an azimuth angle ϕ k and a polar angle θ k , said smartphone comprising at least one processor configured for:

a) setting initial values (ϕ 0 ,θ 0 ) for said azimuth angle ϕ k and said polar angle θ k for loudspeaker l k direction;

b) in a first loop over smartphone position angle α for the determination of one of ϕ k and θ k , and thereafter in a second loop over mobile device position angle α for the determination of the other one of ϕ k and θ k :

c) setting k=1;

d) in a sub-loop over k:

e) in a sub-sub-loop over a rotation angle of said smartphone;

f) receiving for said smartphone being rotated a corresponding measured smartphone rotation angle value α k ;

g) receiving corresponding smartphone microphone signals (y k1 (t), y k2 (t)) from emitted loudspeaker l k test signal;

h) calculating from said microphone signals a corresponding Time Difference of Arrival value (τ k (α k ));

i) if said Time Difference of Arrival value (τ k (α k )) is not zero or is not smaller than a predetermined threshold value, returning to step f);

j) otherwise, calculating a corresponding azimuth ϕ k or polar θ k , respectively, angle value for the position of loudspeaker l k ;

k) incrementing k by ‘1’;

I) if k≤N, returning to step f);

m) otherwise, checking whether both of ϕ k and θ k have been determined, and if not true, returning to step b);

n) after all positions of said N loudspeakers have been determined, providing a corresponding set of N pairs of azimuth and polar angle values ϕ k and θ k for said loudspeakers l k and for all k;

o) using said corresponding set of pairs of azimuth and polar angle values to accurately calibrate said loudspeakers l k .

16. A measurement device for determining the direction of loudspeakers l k in a setup of a surround sound system including N loudspeakers, k=1 . . . N, adapted to cooperate with a smartphone equipped with at least two microphones (m 1 ,m 2 ), wherein said direction is expressed by an azimuth angle ϕ k and a polar angle θ k , said smartphone comprising at least one processor configured for:

a) setting initial values (ϕ 0 ,θ 0 ) for said azimuth angle ϕ k and said polar angle θ k for loudspeaker l k direction;

b) in a first loop over position angle α for the determination of one of ϕ k and θ k , and thereafter in a second loop over smartphone position angle α for the determination of the other one of ϕ k and θ k , said smartphone having a desired azimuth angle or polar angle:

c) setting k=1;

d) in a sub-loop over k:

e) receiving smartphone microphone signals (y k1 (t), y k2 (t)) from emitted loudspeaker l k test signal (s k (t));

f) determining from said captured smartphone microphone signals (y k1 (f), y k2 (t)) a loudspeaker distance difference value (Δ k ) and calculating a corresponding smartphone position angle value (α k );

g) calculating a corresponding azimuth ϕ k or polar θ k , respectively, angle value for the position of loudspeaker l k ;

h) incrementing k by ‘1’;

i) if k≤N, returning to step e);

j) otherwise, checking whether both of ϕ k and θ k have been determined, and if not true, returning to step b);

k) after all positions of said N loudspeakers have been determined, providing a corresponding set of N pairs of azimuth and polar angle values ϕ k and θ k for said loudspeakers l k and for all k;

l) using said corresponding set of pairs of azimuth and polar angle values to accurately calibrate said loudspeakers l k .

17. The measurement device of claim 16 , in which said at least one processor is further configured for:

a) capturing smartphone microphone signals (y k1 (t), y k2 (t)) from loudspeaker l k test signal emitted by a selected loudspeaker l k among said N loudspeakers;

b) receiving for said smartphone a measured smartphone rotation angle value α k corresponding to a rotation of said smartphone;

c) calculating a corresponding Time Difference of Arrival value (τ k (α k ));

d) if said Time Difference of Arrival value (τ k (α k )) is not zero or is not smaller than a predetermined threshold value, returning to step a);

e) otherwise, defining an initial direction angle value β=0;

f) receiving for said smartphone a measured rotation angle value β corresponding to rotating said smartphone by an angle β≈π/4;

g) receiving smartphone microphone signals from emitted loudspeaker l k test signal;

h) calculating from said smartphone microphone signals a loudspeaker distance difference value Δ k and a microphone distance value

d

12

=

Δ

k

sin

⁢

⁢

β

.