Disclosed is a circuit for determining whether an incoming signal is a speech signal or a data signal. In the preferred embodiment, means for separating the incoming signal into a low frequency component and a high frequency component are provided. The low frequency component consists of frequencies below a specified frequency, namely 1000 Hz. and the high frequency component consists of frequencies above 1000 Hz. Means are also provided for the comparison of the energy level of the high frequency components with a multiple of the energy level of the low frequency components. Also, means are provided for comparing a multiple of the energy level of the low frequency components with a maximum threshold and for comparing the energy level of the high frequency components with a minimum threshold. Further, means are provided for detecting whether the incoming signal has a slope. Data is determined to be present when the energy level of the high frequency components exceeds a multiple of the energy level of the low frequency components, and when the energy of the low frequency components is less than a maximum threshold and when the energy level of the high frequency components is greater than a minimum threshold and when the incoming wave has no slope all occurring simultaneously for a preselected period of time.
A system for subband coding of a digital audio signal x(k) includes in the coder (1) a filter bank (3) for splitting the audio signal band, with sampling rate reduction, into subbands (p=1, . . . P) of approximately critical bandwidth and in the decoder (2) a filter bank (5) for merging these subbands, with sampling rate increase. For each subband (p) the coder (1) comprises a detector (7(p)) for determining a parameter G(p;m) representative of the signal level in a block (p;m) of M samples of the subband signal x.sub.p (k) as well as a quantizer (8(p)) for adaptively block quantizing this subband signal in response to parameter G(p;m), and the decoder (2) comprises a dequantizer (9(p)) for adaptively block dequantizing the quantized subband signal s.sub.p (k) in response to parameter G(p;m). The quantizing characteristics are related to the noise-masking curve of the human auditory system, owing to which a high-quality of the replica x(k) of audio signal x(k) is attained with an average number of approximately 2.5 bits per sample for representing the output signals of the coder (1). The occasional audibility of quantizing noise in this replica x(k) is reduced effectively in that the coder (1) and decoder (2) contain identical bit allocation means (23, 24) responsive to a set of parameters G(p;m) for the higher group of subbands (p.sub.im .ltoreq.p.ltoreq.P) within an allocation window (FIG. 5) for allocating a number of B(p;m) bits per sample from a fixed predetermined number of B bits for this allocation window to the quantizer (8(p)) and the dequantizer (9(p)) for the block (p;m) of subband signal x.sub.p (k) and s.sub.p (k), respectively.
A music/speech filter is provided for automatically determining whether an audio signal is music or speech by obtaining a relative measure of the energy in a selective frequency range and, from this determination, controlling the passage or path of the audio signal. The filter can be attached to a radio receiver to selectively pass either music or speech at the option of the user.
Speech versus music is decided by comparing the presence of pauses greater than 32, 60 and 500 ms in the lower input spectrum, and 4 ms in the higher input spectrum.
The present invention classifies an input signal as either voice or data with reduced energy consumption. The present invention includes a frequency estimator and an energy estimator for processing an input signal and a classification unit connected to both the frequency and energy estimators for classifying the input signal. The frequency estimator includes a delay and difference integrator. In operation, the delay receives the input signal and generates a delayed input signal and the difference integrator receives the delayed and input signals and generates a frequency estimate value representing both the estimated central frequency of the input signal and the estimated energy of the input signal. The energy estimator generates an estimate of the energy level of the input signal. The classification unit classifies the input as either voice or data based on a comparison of the frequency and energy estimate values and a data threshold value.
A system for subband coding of a digital audio signal x(k) includes in the coder (1) a filter bank (3) for splitting the audio signal band, with sampling rate reduction, into subbands (p=1, . . . P) of approximately critical bandwidth and in the decoder (2) a filter bank (5) for merging these subbands, with sampling rate increase. For each subband (p) the coder (1) comprises a detector (7(p)) for determining a parameter G(p;m) representative of the signal level in a block (p;m) of M samples of the subband signal x.sub.p (k) as well as a quantizer (8(p)) for adaptively block quantizing this subband signal in response to parameter G(p;m), and the decoder (2) comprises a dequantizer (9(p)) for adaptively block dequantizing the quantized subband signal s.sub.p (k) in response to parameter G(p;m). The quantizing characteristics are related to the noise-masking curve of the human auditory system, owing to which a high-quality of the replica x(k) of audio signal x(k) is attained with an average number of approximately 2.5 bits per sample for representing the output signals of the coder (1). The occasional audibility of quantizing noise in this replica x(k) is reduced effectively in that the coder (1) and decoder (2) contain identical bit allocation means (23, 24) responsive to a set of parameters G(p;m) for the higher group of subbands (p.sub.im .ltoreq.p.ltoreq.P) within an allocation window (FIG. 5) for allocating a number of B(p;m) bits per sample from a fixed predetermined number of B bits for this allocation window to the quantizer (8(p)) and the dequantizer (9(p)) for the block (p;m) of subband signal x.sub.p (k) and s.sub.p (k), respectively.
