Digital signal sub-band separating/combining apparatus achieving band-separation and band-combining filtering processing with reduced amount of group delay
a technology of sub-band separation and filtering, applied in the field of sub-band separation/combining apparatus, can solve the problems of serious disadvantage in the amount of delay, and achieve the effect of reducing the amount of filter delay and more effective suppression
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first embodiment
[0031]FIG. 1 is a general system block diagram of a first embodiment of the invention, which is a combination of a sub-band separating apparatus and a sub-band combining apparatus, for use with a processing (or transmitting / receiving) system. In FIG. 1, a band-separating filter bank 1 performs filtering of respective frequency bands of an input PCM digital signal x(n), then decimation is applied, using a decimation factor of D. The band-separating filter bank 1 is formed of a set of band-separating filters 010˜01n and a corresponding set of down-samplers 020˜02n, each of which applies decimation by a fixed factor D (i.e., selecting one in every D successive samples) to the output sub-band signal from the corresponding one of the band-separating filters 010˜01n. After the resultant decimated sub-band signals have been subjected to predetermined processing in a processing section 3, they are inputted to a band-combining filter bank 2, which effects interpolation of the signals, i.e., ...
second embodiment
[0047]FIG. 4 shows a second embodiment of the invention, which is a PCM digital audio signal compression encoding / decoding apparatus. It should be understood that the invention could of course be applied to various other types of digital signal encoding apparatus. In FIG. 4, an encoder 101 receives as input a PCM digital audio signal, performs sub-band separating processing, and uses human psycho-acoustic response characteristics etc., to perform compression encoding processing. The encoder 101 is formed of a band-separating filter bank 102, psycho-acoustic model section 103, quantization / encoding section 104 and frame forming section 105.
[0048] The band-separating filter bank 102 is formed as described hereinabove for the band-separating filter bank 1 of the first embodiment, for the case in which this is a cosine modulation filter bank in which the band-separating filters are configured in accordance with equation (7) above, with a decimation factor D that is identical to the sep...
third embodiment
[0065]FIG. 5 shows the system configuration of a third embodiment of the invention. This is a wireless microphone system which uses sub-band compression encoding / decoding processing having a low amount of delay, implemented as described above for the second embodiment. As a result with this system, by comparison with the prior art, there is a reduced amount of delay between the time at which a sound is received by a microphone of the system and the time at which a corresponding amplified sound is emitted from a loudspeaker.
[0066] In FIG. a transmitter 200 applies A-D conversion to convert an audio signal from a microphone into a PCM digital audio signal, then applies compression encoding processing as described hereinabove for the second embodiment of the invention, to obtain a compressed bit stream. The bit stream is then subjected to encoding conversion to reduce the effects of errors which may arise when the bit stream traverses a transmission path, and the resultant signal is t...
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