1. Speech enhancement device for the reduction of background noise, comprising a time-to-frequency transformation unit (2) to transform frames of time-domain samples of audio signals to the frequency domain, background noise reduction means (3) to perform noise reduction in the frequency domain, and a frequency-to-time transformation unit (4) to transform the noise reduced audio signals from the frequency domain to the time-domain, characterized in that the background noise reduction means (3) comprise a background level update block (8) to calculate, for each frequency component in a current frame of the audio signals, a predicted background magnitude Bk in response to the measured input magnitude Sk from the time-to-frequency transformation unit (2) and in response to the previously calculated background magnitude B1k, a signal-to-noise ratio block (9) to calculate, for each of said frequency components, the signal-to-noise ratio SNRk in response to the predicted background magnitude Bk and in response to said measured input magnitude Sk and a filter update block (10) to calculate, for each of said frequency components, the filter magnitude Fk for said measured input magnitude Sk in response to the signal-to-noise ratio SNRk.
2. Speech enhancement device according to claim 1, characterized in that the background level update block (8) comprises a memory unit (20) to obtain the previously calculated background magnitude B1k, processing means (12-16) and comparator means (17) to update the previously predicted background magnitude according to the relation:
BkmaxminBk, Bk, Bmin,
with Bmin the minimum allowed background level, while
BkB1k. Uk and
Bk(Bk.Dk)(Sk.C.(1Dk)), in which Uk and Dk are frequency dependent scaling factors and C a constant.
3. Speech enhancement device according to claim 1 or 2, characterized in that the signal-to-noise ratio block (9) comprises means to calculate the signal-to-noise ratio SNRk in response to the predicted background magnitude Bk and to the measured input magnitude Sk according to the relation:
SNRkSkBk.
4. Speech enhancement device according to any one of the preceding claims, characterized in that the filter update block (10) comprises first means to calculate an internal filter value Fk and second means to derive therefrom the filter magnitude for the measured input magnitude, the first means comprising a memory unit (31) to obtain a previously calculated internal filter magnitude F1k and processing means (21-23, 25-27) to update the previously calculated internal filter magnitude.
5. Speech enhancement device according to claim 4, characterized in that the second means comprise comparator means (28) for scaling and clipping the filter magnitude according to the relation:
FkmaxminH.Fk, 1, Fmin, where
H is a constant, Fmin a minimal filter value and Fk the internal filter value.
6. Speech encoder for a speech coding system, particularly for a P2CM audio coding system, provided with a speech enhancement device according to any one of the preceding claims.
7. Speech coding system, particularly a P2CM audio coding system, provided with a speech encoder having a speech enhancement device according to any one of the preceding claims.
8. P2CM audio coding system with a P2CM encoder comprising a pre-processor including spectral amplitude warping means and an ADPCM encoder, characterized in that the pre-processor is provided with a speech enhancement device according to any one of the claims 1-5, the speech enhancement device having background noise reduction means, integrated in the spectral amplitude warping means of the pre-processor.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
What is claimed is:
1. In a method in which a feedstock containing an organic halide either alone or in admixture with an organic compound is gasified or atomized and subjected to the reaction with calcium oxide, barium oxide or a mixture thereof that are heated at 400-700 C., whereby the halogen in the organic halide is converted to a calcium halide andor a barium halide, the improvement wherein a bed of calcium oxide andor barium oxide in particulate form is continuously moved through the reaction zone such that it enters into countercurrent reaction with the feedstock and the reaction is performed in a reaction column equipped with an agitatingmoving means by which the halide which is the product of reaction between the organic halide and said oxide is continuously discharged to the outside of the reaction zone.
2. In an apparatus in which a feedstock containing an organic halide either alone or in admixture with an organic compound is gasified or atomized and subjected to the reaction with calcium oxide, barium oxide or a mixture thereof that are heated at 400-700 C., whereby the halogen in the organic halide is converted to a calcium halide andor a barium halide, the improvement comprising:
a) a means for gasifying or atomizing the feedstock containing the organic halide either alone or in admixture with the organic compound;
b) a heating means for heating the particles of calcium oxide andor barium oxide at a controlled temperature of 400-700 C.;
c) a means for supplying the particles of calcium oxide andor barium oxide continuously; and
d) a reaction column equipped with a supply section for the feedstock as supplied from said gasifying or atomizing means and which contains the organic halide either alone or in admixture with the organic compound, a reactive section which is heated by said heating means and in which a moving bed of said oxide particles is continuously brought into countercurrent reaction with said feedstock so that the halogen in the organic halide is converted to a calcium halide andor a barium halide, and an agitatingmoving means by which said resulting calcium halide andor barium halide is continuously discharged to the outside of the reaction system.