Patent ID: 12212928

Mutually corresponding parts and variables are each provided with the same reference signs throughout the figures.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the figures of the drawing in detail and first, in particular, toFIG.1thereof, there is shown a timing diagram over a time t to schematically show the level values P from a first level measurement p1(solid line) and a second level measurement p2(dashed line). Each of the level measurements p1and p2is performed on an audio signal (not shown in more detail). At an instant T0the audio signal contains an isolated sound event4(dotted line), which firstly has a clearly defined end and secondly gives rise to contributions by acoustic reverberation in the audio signal (not shown) due to the physical surroundings in which the audio signal was recorded to generate it. The sound event4in this case is meant to have only a very short length of time z. All of the sound energy of the sound event4is therefore concentrated in this length of time z. This can be the case for example for a bang, a thump, a slap, but also for consonants in speech, in particular for plosives, and for similar sounds of very short duration.

The first level measurement p1has a first attack time6, which passes by after the instant T0, at which the sound event4starts, until the first level measurement has assumed a predefined proportion8of the asymptotic level10, the asymptotic level10corresponding to the level that the first level measurement would assume for a steady-state, continuous sound event with a signal level identical to the sound event4. The second attack time12of the second level measurement p2is identical to the first attack time6of the first level measurement in the present case.

For this reason, the first level measurement p1and the second level measurement p2have the same attack response, and therefore assume the same maximum value14for the level, which is just below the asymptotic level10, at the instant T1, which marks the end of the length of time z and therefore the end of the sound event4.

At the instant T1the decay response characterized by the reverberation now starts in the real acoustic situation represented by the audio signal, as a result of which the decay responses of the first level measurement p1and the second level measurement p2now also merge according to the respective decay time.

The attack response and the decay response of the first and second level measurements p1, p2are schematically shown linearly here, as a result of which a peak is also obtained at the transition from the attack response to the decay response in this representation. The attack response may already rise more slowly before that transition, however, and the transition can in particular also take place in a smooth manner.

The first level measurement p1and the second level measurement p2have a first decay time16and a second decay time18, respectively, the second decay time18being longer than the first decay time16. The second decay time can be expressed in relation to the decay time constant T60, according to which a sound level has decreased from a maximum value by 60 dB, and is often used as a measure of a decay in a room, as follows: the “decay rate” of the second level measurement is provided by the difference between the maximum value14and the initial value24, divided by the second decay time18; in the present case, this decay rate corresponds to a rate of 60 dB/T60. The first decay time16can be provided for example by half of the second decay time18(or a similar value), and determines in particular the beginning of the decay response15of the first level measurement p1(see dotted line to extrapolate the first decay time16).

The first and second level measurements p1, p2are each implemented as a first-order asymmetric recursive low-pass filter, as a result of which an applicable decay parameter of the filter, which controls the perpetuation of existing level values for the next particular instant in the level measurement p1, p2(cf. equation (i), see above), can be used to adjust the respective decay time16,18. For the second level measurement p2, the second decay time18thus adjusted is slow enough for the decay response to be provided by the linear regression of the filter. Although the acoustic contributions by the diffuse reverberation of the reverberation tail may contribute to the value of the second level measurement p2, they do not determine the decay response thereof.

For the first level measurement p1, on the other hand, the first decay time16is such that, after a first peak15, which corresponds to the maximum value14and is provided by the sound event4, and after a fall17at a speed corresponding to the first decay time16(in the event of which fall the first and early reflections may still contribute to the audio signal), there is a transition to a shallower edge19at an instant T2. In this edge, the gradually decreasing contributions by the diffuse reverberation actually “feed” the first level measurement p1, and therefore determine its decay response in this area.

Since the decay response in the shallower edge19of the first level measurement p1is thus actually determined by the diffuse reverberation that decays with the decay time T60in the room, this exponential decay response from the instant T2in the logarithmic representation of the first level measurement p1is parallel to the decay response of the second level measurement p2, until the first level measurement has dropped to the initial value24before the sound event4at an instant T3: the diffuse reverberation in the room in which the audio signal was generated has therefore died away. Due to the longer second decay time18, the second level measurement p2does not drop to the initial value24until at a later instant T4, on the other hand. The initial value24can be provided, for instance, by background noise in the audio signal.

FIG.2uses a timing diagram to schematically show a difference Δ between the first level measurement p1and the second level measurement p2shown inFIG.1(dashed line). Owing to the fact that p1and p2are both equal to the initial value24up to the instant T0, and have the same attack response up to the instant T1owing to the identical first and second attack times6,12, the difference Δ=p1−p2is equal to exactly 0 up to the instant T1. Owing to the different first and second decay times16,18(seeFIG.1), the difference Δ drops to a minimum value min<0 up to the instant T2, and remains at said minimum value min between the instants T2and T3(seeFIG.1, parallel curve) owing to the identical decay response of the two level measurements p1, p2. Not until after the instant T3, from which the first level measurement p1has already assumed the initial value24, to which the second level measurement p2still falls up to the instant T4(seeFIG.1), does the absolute value of the difference Δ decrease again, i.e. the difference Δ rises back to the value zero up to the instant T4.

The difference Δ is now compared with a first limit value th1, the comparison being intended to be used to ascertain a contribution by diffuse reverberation in the second level measurement p2in a manner that will be described. The absolute value of the first limit value is lower than the absolute value of the minimum value min, that is to say |th1|<|min|, or 0>th1>min.

The first limit value th1should preferably be chosen such that the minimum value min of the difference Δ can be reliably identified by way of an appropriate comparison. It is therefore assumed that if Δ<th1(that is to say if the difference Δ is below the first limit value th1), there is a contribution30by diffuse reverberation in the audio signal, since firstly the decay response of the first level measurement p1for the period of time between the relevant instants T2and T3is provided directly by said diffuse reverberation, whereas the decay response of the second level measurement p2is still largely provided by the original sound event4owing to the slow second decay time18, the contribution30by the diffuse reverberation also being included in the second level measurement p2, however.

The difference Δ=p1−p2and the first limit value are now used to form a correction function d (solid line) on the basis of equation (iii). This correction function d is formed by the first limit value th1up to an instant T1′>T1(with T1′<T2), and transitions into the difference Δ for t>T1′. At an instant T3′>T3(with T3′<T4), the correction function d is provided by the first limit value th1again.

The benefit of this correction function d becomes clear fromFIG.3:FIG.3uses a timing diagram to schematically show the second level measurement p2(solid line) as inFIG.1. In addition, a reverberation interference level prn (dashed line) provided by the second level measurement p2, from which the correction signal d shown inFIG.2was subtracted, is shown. Since the first level measurement p1is determined by the contributions by the diffuse reverberation for the period of time between the instants T2and T3, and, although said contributions are likewise incorporated in the second level measurement p2in this period of time, said second level measurement is determined primarily by the contribution by the sound event4that decays according to the second decay time18(that is to say the “isolated” decaying contribution, without newly added sound contributions), the correction function d is essentially provided by the decaying contribution by the sound event4in the second level measurement p2between the instants T2and T3(or, based on the transitions, even between T1′ and T3′). In other words, between the instants T2and T3, the actual sound power is essentially equal to the first level measurement p1, and so the (negative) correction function d is added to the second level measurement p2in order to likewise attain the actual sound power in the reverberation interference level prn in this interval. The second level measurement p2is always above the actual sound power and therefore also above the power of the diffuse reverberation.

The reverberation interference level prn=p2+d is therefore essentially provided by the diffuse reverberation in said period of time. Before the instant T1′ and after the instant T3′, the reverberation interference level prn is provided by the constant offset owing to the first limit value th1in the correction function d.

FIG.4uses a timing diagram to schematically show the reverberation interference level prn (dashed line) and the first level measurement p1(solid line). In the period of time between the instants T2and T3, in which the first level measurement p1is determined by the diffuse reverberation, the two said lines are essentially one on top of the other. Even though a schematic, idealized representation is shown in the present case, the real case will be similar, namely the two lines will each provide almost identical values in the region of the diffuse reverberation.

If a gain factor is now determined in a frequency band on the basis of equation (ii), and is applied to the signal component of the audio signal50in the frequency band, the diffuse reverberation (between the instants T2and T3) can be eliminated, while the other contributions by the audio signal50in the frequency band are preserved, since it then holds that p1>prn there.

The method illustrated on the basis ofFIG.1for eliminating the acoustic reverberation in the audio signal can be performed in particular on a frequency band by frequency band basis in this case. To this end, the audio signal is split into respective individual frequency bands, in each of which the first and second level measurements p1, p2are performed as shown. The attenuation of the audio signal can then be controlled for each frequency band individually on the basis of the respective gain parameter G ascertained in this frequency band according to the attack response and the decay response.

FIG.5uses a block diagram to schematically show a hearing instrument40that comprises an input transducer42, a signal processing unit44and an output transducer46. The input transducer42, which in the present case is provided by a microphone, generates the audio signal50from a sound signal48from the surroundings that also incorporates a specific sound event4. Acoustic reverberation of the sound signal4in the audio signal50can now be eliminated in the signal processing unit44in the manner described on the basis ofFIG.1or in the manner described on the basis ofFIG.2. The resultant signal is processed further, in particular subjected to dynamic compression and to frequency-band-dependent amplification, and an output signal52is generated therefrom, which is converted into an output sound signal54by the output transducer46.

Although the invention has been illustrated and described more thoroughly in detail by way of the preferred exemplary embodiment, the invention is not limited by this exemplary embodiment. Other variations can be derived therefrom by a person skilled in the art without departing from the scope of protection of the invention.

The following is a summary list of reference numerals and the corresponding structure used in the above description of the invention:4sound event6first attack time8predefined proportion10asymptotic level12second attack time14maximum value15peak16first decay time17fall18second decay time19shallower edge24background noise40hearing device42input transducer44signal processing unit46output transducer48sound signal50audio signal52output signal54output sound signald correction functionmin minimum valueP level valuesp1first level measurementp2second level measurementprn reverberation interference levelt timeth1first limit valueT0-T4instantT1′, T3′ instantz length of timeΔ difference