PCM Passband Filter Architecture for Multi-Band Audio Phase Alignment
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Solution Overview
Problem
Existing audio filter technologies face challenges in achieving high-fidelity audio processing, particularly in dividing the audio band into multiple bands without significant phase shift distortion and maintaining operational efficiency with high-speed audio pulse code modulation (PCM) streams.
Innovation Solution
A pulse code modulation passband filter is designed using delay circuits, frequency reduction and raising circuits, and adders to downsample, upsample, and phase-align PCM streams, allowing for the creation of multiple filter passbands and a multi-channel digital passband filter, enabling efficient division of the audio range into multiple bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If DSP is used for FIR calculations to construct a digital passband filter, then phase shift distortion is reduced and maintenance is simplified, but the operation speed cannot effectively frequency divide high-speed audio PCM streams (24 bit/192 Kfs and higher)
Solution Approach 1:
The audio frequency spectrum is segmented into multiple passbands (first passband, second passband, third passband, etc.) using separate filtering paths. Each path processes a specific frequency range independently, allowing parallel processing that increases overall throughput while maintaining low phase distortion through dedicated FIR filters for each segment.
Solution Approach 2:
The patent transitions from time-domain processing to frequency-domain processing by introducing multiple parallel filtering paths that operate on different frequency bands simultaneously. This dimensional transformation in the signal processing approach enables high-speed handling of 192 Kfs PCM streams while maintaining audio fidelity through frequency-selective filtering.
2Device complexity
If passive parts are used to construct passband filters, then the structure is simple, but phase shift distortion is large and maintenance is difficult
Solution Approach 1:
The patent replaces passive mechanical/electrical filter components with digital signal processing elements. Instead of using passive LC circuits or RC networks that introduce phase distortion, the invention employs digital FIR filters implemented in a programmable manner, eliminating the phase shift problems inherent in passive analog filtering while maintaining structural simplicity through software-based filter coefficients.
3Adaptability or versatility
If the audio band is divided into multiple bands with separate passband filters, then each band can be controlled independently, but the number of required passband filters increases
Solution Approach 1:
The patent implements a universal filtering architecture where multiple passband filters share common computational resources and processing paths. The first, second, third and subsequent passband filters are constructed using the same FIR filtering methodology and can be controlled independently through separate gain adjustments, achieving band-specific control flexibility without proportionally increasing the number of physical filter components.
Data Source
AI summary
A 1st frequency reduction circuit of a filter of the invention downsamples the sampling rate of a signal source to a predetermined value to obtain a 1st PCM stream, a 1st frequency raising circuit raises the sampling rate of the 1st PCM stream to be the same as that of the signal source, a 1st delay circuit delays a stream of the signal source, such that its phase is the same as that of the 1st PCM stream, a 1st adder subtracts the frequency raised 1st PCM steam from the delayed stream of the signal source to obtain a passband 1, a j-th frequency reduction circuit downsamples the sampling rate of a (j−1)-th PCM stream to a predetermined value to obtain a j-th PCM stream, wherein 2≤j≤n, a j-th frequency raising circuit raises the sampling rate of the j-th PCM stream to be the same as that of the (j−1)-th PCM stream, a j-th delay circuit delays the (j−1)-th PCM stream, such that its phase is the same as that of the j-th PCM stream, a j-th adder subtracts the frequency raised j-th PCM stream from the delayed (j−1)-th PCM stream to obtain a passband j, and when j=n, the j-th PCM stream is a passband n+1.