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stereo decoder
Vertaling van "stereo decoder" in Chinees
立体声解码器
Section B will describe the first main embodiment. In this embodiment, special hardware is implemented in the FM stereo decoder that produces a 搎uadrature-demodulated L-R noise.? The basic idea is to demodulate the L-R signal with a special carrier that is 90 degrees out of phase with the carrier that is normally used to demodulate the L-R signal. Because this special carrier is 搊rthogonal? to the normal carrier for the L-R signal, it will not pick up the L-R signal and will instead produce a quadrature-demodulated version of the L-R noise. Such quadrature-demodulated L-R noise will not have the same sample values as the true noise in the demodulated L-R signal, but will have roughly the same average magnitude spectrum when compared with the true noise in the demodulated L-R signal. Thus, the L-R noise floor can easily and reliably be obtained by computing the magnitude spectrum of this quadrature-demodulated L-R noise. Once the L-R noise floor is obtained, the L+R noise floor can then be estimated through table look-up and interpolation along the frequency and CNR axes based on empirically derived tables. Furthermore, the average power of the quadrature-demodulated L-R noise is also used by this first main embodiment to estimate the CNR.
B部分将对第一主要实施例进行说明。在该实施例中，产生"正交解调L-R噪声"的FM立体声解码器中使用专用硬件。基本理念是，用与通常用于解调L-R信号的载波成90度异相的特殊载波解调L-R信号。由于该特殊载波与用于L-R信号的正常载波 ¡º正交 ¡±，其不会拾取L-R信号，相反，会产生正交解调版的L-R噪声。这种正交解调L-R噪声的样本值将与解调L-R信号中的真实噪声不同，但与解调L-R信号中的真实噪声相比时，平均幅度谱基本相同。因此，L-R本底噪声可容易可靠地通过计算该正交解调L-R噪声的幅度谱而获取。获取L-R本底噪声之后，可基于实证表通过沿频率和CNR轴的查表和内插法而估算L+R本底噪声。另外，正交解调L-R噪声的平均功率还由该第一主要实施例用于估算CNR。
A second main embodiment of a system for enhancing the audio quality of an FM receiver will now be described. As discussed above, the first main embodiment utilizes special hardware in the FM stereo decoder to generate a quadrature-demodulated L-R noise signal that provides a reliable representation of the L-R noise floor. This L-R noise floor is then used to estimate the L+R noise floor and the CNR. However, in the second main embodiment, it is assumed that no special hardware is available to produce the quadrature-demodulated L-R noise. Rather in the second main embodiment, the L+R signal is sampled at a high enough sampling rate to allow the extraction of the stop band signal between 15 and 23 kHz (see FIG. 1). After suppressing the 19 kHz stereo pilot tone and possible further band selection to avoid some spurious tones, the average power of this stop band signal is then combined with table look-up and interpolation along the frequency and CNR axes to estimate the L-R noise floor, L+R noise floor, and CNR based on empirically derived tables. L+R pop suppression, L-R and L+R noise suppression, and L-R and L+R fast fading compensation may then be performed in generally the same manner as described above in reference to the first main embodiment.
现在将对用于增强FM接收机的音频质量的系统的第二主要实施例进行说明。如上所述，第一主要实施例利用FM立体声解码器中的专用硬件生成提供L-R本底噪声的可靠表示的正交解调L-R噪声信号。该L-R本底噪声随后用于估算L+R本底噪声和CNR。但是，在第二主要实施例中，假定没有专用硬件可用于产生正交解调L-R噪声。相反，在第二主要实施例中，以足够高的采样率对L+R信号进行采样，以提取15和23 kHz之间的阻带信号（见图1）。抑制19 kHz立体声导频音，以及为避免某些乱真音而可能进行的进一步频带选择之后，该阻带信号的平均功率可与沿频率和CNR轴的查找表和内插法组合，以基于根据经验得出的表估算L-R本底噪声、L+R本底噪声和CNR。随后可以与上述第一主要实施例基本相同的方式进行L+R爆裂抑制、L-R和L+R噪声抑制和L-R和L+R快衰落补偿。
With continued reference to FIG. 13, L+R pop suppression logic 306 includes switching logic, which is symbolically represented by a first switch 1302 and a second switch 1304. This switching logic compares an estimated CNR received from CNR estimation logic 302 with a threshold for pop appearance. If the estimated CNR exceeds the threshold, then the switching logic passes the L+R signal received from FM stereo decoder 202 directly to the output of L+R pop suppression logic 306 without modifying it. Symbolically, this would be represented in FIG. 13 by placing switches 1302 and 1304 in an 搖p? position. This bypassing of the pop suppression function is performed because, at higher CNRs, there will be very few or no noise pulses in the L+R signal and thus there will be no benefit to applying pop suppression. Rather, applying pop suppression at such higher CNRs can cause false detections to occur, which can actually result in the undesired introduction of noise pulses into the L+R signal.
继续如图13所示，L+R爆裂抑制逻辑306包括开关逻辑，开关逻辑用符号表示为第一开关1302和第二开关1304。该开关逻辑将从CNR估算逻辑302接收的估算CNR与出现爆裂的阈值相比较。如果估算CNR超过阈值，开关逻辑在不进行修正的情况下直接将从FM立体声解码器202接收的L+R信号传递到L+R爆裂抑制逻辑306的输出端。若用符号表示，在图13中通过将开关1302和1304置于 ¡º上 ¡±位置来表示。跳过爆裂抑制功能的原因在于，在较高CNR下，L+R信号中的噪声脉冲非常少，或没有噪声脉冲，因此，实施爆裂抑制没有益处。相反，在这种较高CNR下实施爆裂抑制会造成错误检测，实际上会将噪声脉冲意外引入L+R信号。
As noted above, if the estimated CNR is less than or equal to the threshold for pop suppression, then the switching logic causes the L+R signal received from FM stereo decoder 202 to be passed to logic blocks 1306, 1308 and 1320 for the purposes of performing pop suppression. Logic block 1306 performs a so-called linear predictive coding (LPC) analysis (also referred to as a short-term prediction analysis) on the current frame of the L+R signal in the time domain. Logic block 1306 performs the LPC analysis to determine the coefficients of an LPC predictor that predicts the value of each sample of the current frame as the weighted sum of a number of prior samples. Logic block 1308 uses the LPC predictor obtained by logic block 1306 to compute an LPC prediction error, which may also be referred to as the short-term prediction error or short-term prediction residual. In particular, for each sample in the current frame of the L+R signal, logic block 1308 subtracts the predicted value of the sample obtained using the LPC predictor from the actual value of the sample to obtain a sample of the LPC prediction error. The foregoing operations are intended to produce a representation of the L+R signal from which the short-term redundancies of the audio signal have been removed.
如上所述，如果估算CNR小于或等于爆裂抑制阈值，开关逻辑将从FM立体声解码器202接收的L+R信号传递给逻辑块1306、1308和1320，以进行爆裂抑制。逻辑块1306在时域内对L+R信号的当前帧进行线性预测编码（LPC）分析（还称为短期预测分析）。逻辑块1306进行LPC分析，以确定LPC预测器的系数，所述LPC预测器预测当前帧的每个样本的值，作为多个先前样本的加权和。逻辑块1308使用逻辑块1306获取的LPC预测器计算LPC预测误差（还称为短期预测误差或短期预测残差）。特别地，对于L+R信号的当前帧中的每个样本，逻辑块1308从样本的实际值中减去利用LPC预测器获取的样本的预测值，以获取LPC预测误差的样本。前述操作用于生成消除了音频信号的短期冗余的L+R信号的表示。
FIG. 2 is a block diagram of an example system for enhancing the audio quality of an FM receiver in accordance with a first main embodiment, the system including an FM stereo decoder and FM audio enhancement logic.
图2为用于增强根据第一主要实施例的FM接收机的音频质量的示例系统的框图，所述系统包括FM立体声解码器和FM音频增强逻辑。
FIG. 2 is a block diagram of an example system 200 for enhancing the audio quality of an FM receiver in accordance with a first main embodiment. System 200 may be implemented, for example, as an integrated part of an FM receiver or as an integrated part of a system that includes an FM receiver. As shown in FIG. 2, system 200 includes at least an FM stereo decoder 202 and FM audio enhancement logic 204. Each of these components will now be briefly described.
图2为用于增强根据第一主要实施例的FM接收机的音频质量的示例系统200的框图。系统200可实施为（例如）FM接收机的集成部分，或包括FM接收机的系统的集成部分。如图2所示，系统200至少包括FM立体声解码器202和FM音频增强逻辑204。现在将对每个部件进行简要说明。
As further shown in FIG. 2, the L+R signal, the L-R signal and the quadrature-demodulated L-R noise signal produced by FM stereo decoder 202 are passed to FM audio enhancement logic 204. In one implementation, each of these signals is a 32 kHz signal. FM audio enhancement logic 204 processes the L+R signal in a manner to be described herein to produce an enhanced L+R signal. FM audio enhancement logic 204 also processes the L-R signal in a manner to be described herein to produce an enhanced L-R signal. FM audio enhancement logic 204 uses the quadrature-demodulated L-R noise signal in a manner to be described herein to estimate a CNR of the input FM radio signal and to estimate noise floors of the L-R and L+R signals. The estimated CNR and the estimated noise floors are used to drive certain aspects of the processing of the L+R and L-R signals, as will also be described herein.
如图2进一步所示，L-R信号和FM立体声解码器202生成的正交解调L-R噪声信号传递给FM音频增强逻辑204。在一个实施方式中，这些信号中的每个均为32 kHz信号。FM音频增强逻辑204以本文所述的方式处理L+R信号，以生成增强L+R信号。FM音频增强逻辑204还以本文所述的方式处理L-R信号，以生成增强L-R信号。FM音频增强逻辑204以本文所述的方式使用正交解调L-R噪声信号估算输入FM无线电信号的CNR，并估算L-R和L+R信号的本底噪声。估算CNR和估算本底噪声用于驱动L-R和L+R信号的处理的特定方面，如本文所述。
As shown in FIG. 3, CNR estimation logic 302 operates to receive the quadrature-demodulated L-R noise signal that is produced by FM stereo decoder 202. CNR estimation logic 302 uses this signal to generate a current estimate of the CNR for each frame of the L-R and L+R signals. In particular, CNR estimation logic 302 determines an average power of the quadrature-demodulated L-R noise signal for a current frame and then generates an estimated CNR for the current frame based on estimated CNR for a frame is used to control whether and/or to what degree each of L+R pop suppression, noise suppression and fast fading compensation are performed for that frame.
如图3所示，CNR估算逻辑302用于接收FM立体声解码器202生成的正交解调L-R噪声信号。CNR估算逻辑302使用该信号为L-R和L+R信号的每个帧生成当前估值。特别地，CNR估算逻辑302为当前帧确定正交解调L-R噪声信号的平均功率，随后基于该值为当前帧生成估算CNR。一个帧的估算CNR用于控制是否为该帧进行L+R爆裂抑制、噪声抑制和快衰落补偿及/或进行到何种程度。
Generally speaking, FM stereo decoder 202 is a component that is configured to perform signal processing operations on an input FM radio signal in order to produce an L+R signal, an L-R signal and a quadrature-demodulated L-R noise signal. FM stereo decoder 202 may receive the input FM radio signal, for example, from an antenna or from a signal processing component that is connected to an antenna (e.g., a downsampler). In one embodiment, FM stereo decoder 202 is implemented in hardware, using analog and/or digital circuits. As shown in FIG. 2, FM stereo decoder 202 includes at least an FM demodulator 212, an L+R filter 214, pilot signal recovery logic 216 and L-R recovery logic 218.
一般来说，FM立体声解码器202是一种用于对输入FM音频信号进行信号处理操作，以生成L+R信号、L-R信号和正交解调L-R噪声信号的部件。FM立体声解码器202可从（例如）天线或与天线连接的信号处理部件（例如，下采样器）接收输入FM无线电信号。在一个实施例中，FM立体声解码器202实施为使用模拟和/或数字电路的硬件。如图2所示，FM立体声解码器202至少包括FM解调器212、L+R滤波器214、导频信号恢复逻辑216和L-R恢复逻辑218。
Furthermore, in the description provided above, pop suppression is said to be performed on an L+R signal, noise suppression is said to be performed on an L-R signal and on a pop-suppressed L+R signal, and fast fading compensation is said to be performed on a noise-suppressed L-R signal and a noise-suppressed L+R signal. However, it is to be understood that any of the foregoing processes can each be performed directly on the L+R and L-R signals produced by the FM stereo decoder or upon a processed version of such L+R or L-R signals. Thus, in the appended claims, any reference to an L+R signal is intended to broadly represent an L+R signal produced by an FM stereo decoder as well as any processed version of such L+R signal and any reference to an L-R signal is intended to broadly represent an L-R signal produced by an FM stereo decoder as well as any processed version of such LR signal. Additionally, it is possible that any of the signal processing techniques described herein as being performed on an L+R signal and/or an L-R signal may also be performed on an L signal obtained by adding the L+R signal and L-R signal and/or on an R signal obtained by subtracting the L-R signal from the L+R signal.
另外，在上文的说明中，对L+R信号进行爆裂抑制，对L-R信号和爆裂抑制L+R信号进行噪声抑制，对噪声抑制L-R信号和噪声抑制L+R信号进行快衰落补偿。但是，应理解的是，可分别对FM立体声解码器生成的L+R和L-R信号或这些L+R或L-R信号的处理版直接进行任何上述过程。因此，在附加权利要求中，提到的任何L+R信号都广泛指FM立体声解码器生成的L+R信号，以及这种L+R信号的任何处理版，提到的任何L-R信号都广泛指FM立体声解码器生成的L-R信号，以及这种L-R信号的任何处理版。另外，本文所述的对L+R信号和/或L-R信号实施的任何信号处理技术还可实施于通过增加L+R信号和L-R信号而获取的L信号，和/或通过从L+R信号中减去L-R信号而获取的R信号上。
Although the foregoing description of the second main embodiment refers to extracting a stop band noise signal from an L+R signal produced by an FM stereo decoder, persons skilled in the relevant art(s) will appreciate that the stop band noise signal may also be extracted from an L-R signal produced by an FM stereo decoder. Accordingly, in an alternate embodiment, stop band noise extraction logic 1916 operates to extract the stop band noise signal from an L-R signal generated by an FM stereo decoder rather than from an L+R signal generated by the FM stereo decoder.
上文的第二主要实施例对从FM立体声解码器生成的L+R信号中提取阻带噪声信号的过程进行了说明，但相关领域的技术人员应理解的是，还可从FM立体声解码器生成的L-R信号中提取阻带噪声信号。由此，在一个替代实施例中，阻带噪声提取逻辑1916用于从FM立体声解码器生成的L-R信号中提取阻带噪声信号，而不是从FM立体声解码器生成的L+R信号中提取阻带噪声信号。
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