Speech encoding apparatus and speech encoding method
First Claim
1. A speech encoding apparatus, comprising:
- a first encoder that encodes a low band spectrum having a lower band than a threshold frequency of a speech signal;
a flattening circuit that flattens the low band spectrum using an inverse filter with inverse characteristics of a spectral envelope of the speech signal; and
a second encoder that encodes a high band spectrum having a higher band than the threshold frequency of the speech signal using the flattened low band spectrum, whereinthe second encoder modifies the flattened low band spectrum such that a dynamic range of the flattened low band spectrum is adjusted to be closer to a dynamic range of the high band spectrum and encodes the high band spectrum using the modified low band spectrum, andthe second encoder modifies the flattened low band spectrum using an encoding candidate that decreases a dynamic range preferentially over an encoding candidate that increases the dynamic range, among a plurality of encoding candidates.
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Accused Products
Abstract
There is provided an audio encoding device capable of maintaining continuity of spectrum energy and preventing degradation of audio quality even when a spectrum of a low range of an audio signal is copied at a high range a plurality of times. The audio encoding device (100) includes: an LPC quantization unit (102) for quantizing an LPC coefficient; an LPC decoding unit (103) for decoding the quantized LPC coefficient; an inverse filter unit (104) for flattening the spectrum of the input audio signal by the inverse filter configured by using the decoding LPC coefficient; a frequency region conversion unit (105) for frequency-analyzing the flattened spectrum; a first layer encoding unit (106) for encoding the low range of the flattened spectrum to generate first layer encoded data; a first layer decoding unit (107) for decoding the first layer encoded data to generate a first layer decoded spectrum, and a second layer encoding unit (108) for encoding.
22 Citations
10 Claims
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1. A speech encoding apparatus, comprising:
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a first encoder that encodes a low band spectrum having a lower band than a threshold frequency of a speech signal; a flattening circuit that flattens the low band spectrum using an inverse filter with inverse characteristics of a spectral envelope of the speech signal; and a second encoder that encodes a high band spectrum having a higher band than the threshold frequency of the speech signal using the flattened low band spectrum, wherein the second encoder modifies the flattened low band spectrum such that a dynamic range of the flattened low band spectrum is adjusted to be closer to a dynamic range of the high band spectrum and encodes the high band spectrum using the modified low band spectrum, and the second encoder modifies the flattened low band spectrum using an encoding candidate that decreases a dynamic range preferentially over an encoding candidate that increases the dynamic range, among a plurality of encoding candidates. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A speech encoding method, comprising:
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encoding, by a first encoder, a low band spectrum having a lower band than a threshold frequency of a speech signal; flattening, by a flattering circuit, the low band spectrum using an inverse filter with inverse characteristics of a spectral envelope of the speech signal; and encoding, by a second encoder, a high band spectrum having a higher band than the threshold frequency of the speech signal using the flattened low band spectrum, wherein the second encoder modifies the flattened low band spectrum such that a dynamic range of the flattened low band spectrum is adjusted closer to a dynamic range of the high band spectrum and encodes the high band spectrum using the modified low band spectrum, and the second encoder modifies the flattened low band spectrum using an encoding candidate that decreases a dynamic range preferentially over an encoding candidate that increases the dynamic range, among a plurality of encoding candidates.
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Specification