Recursive IIR Filter for TV Stereo Difference-Channel Noise

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Solution Overview

Problem

The BTSC system introduces additional noise into stereo audio signals due to the placement of the Difference channel subcarrier, which can render the stereo signal too noisy to meet FCC requirements, and there is a need to reduce the cost of noise reduction systems in television receivers and encoders.

Innovation Solution

A configurable infinite impulse response digital filter is used to selectively apply filter coefficients to the Difference signal in a recursive manner, preparing it for transmission and decoding, which can be implemented in integrated circuits to reduce noise and cost.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If the Difference channel subcarrier is placed at 31.768 kHz above the aural carrier's center frequency, then stereo audio transmission is enabled, but additional noise is introduced into the Difference channel making the stereo signal too noisy to meet FCC requirements

Engineering Contradiction:

Improvestereo audio transmission capabilityVSAvoidnoise in Difference channel

Core Design Contradiction:

Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

The patent applies companding (compression-expansion) to convert the harmful noise introduced by the subcarrier placement into a manageable condition. The encoder compresses the Difference signal dynamically, and the decoder expands it, such that the noise picked up during transmission is masked by the signal content after expansion, transforming the noise problem into an acceptable audio quality outcome

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The patent changes the parameter of signal amplitude distribution through companding. The encoder adaptively adjusts the compression ratio based on signal characteristics, and the decoder applies corresponding expansion, effectively altering the signal-to-noise ratio parameters to meet FCC requirements while maintaining stereo transmission

Inventive Principle:

Principle #35Parameter changes

2Object-affected harmful factors

If a noise reduction system is implemented in the Difference channel signal path, then noise is reduced to meet FCC requirements, but manufacturing costs of encoders and decoders increase

Engineering Contradiction:

Improvenoise in Difference channelVSAvoidmanufacturing cost of decoder

Core Design Contradiction:

Object-affected harmful factorsVSEase of manufacture

Solution Approach 1:

The patent implements a single configurable infinite impulse response digital filter that can perform multiple filtering functions (low pass, high pass, band pass, notch filtering) by selectively applying different filter coefficients. This multi-functional approach eliminates the need for separate dedicated filters for each function, reducing the number of components required in the decoder and thereby reducing manufacturing costs while still achieving noise reduction

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The patent uses a configurable filter that can change its parameters (filter coefficients, cutoff frequencies, filter order) dynamically based on the input signal characteristics and desired output. This parameter adaptability allows a single filter structure to replace multiple fixed filters, reducing hardware complexity and manufacturing cost while maintaining effective noise reduction across different operating conditions

Inventive Principle:

Principle #35Parameter changes

3Adaptability or versatility

If multiple filters are used in the encoder and decoder, then various filtering functions are achieved, but device complexity and manufacturing cost increase

Engineering Contradiction:

Improvefiltering function capabilityVSAvoidnumber of filters in encoder and decoder

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent employs a single configurable infinite impulse response digital filter that can be reconfigured to perform low pass filtering, high pass filtering, band pass filtering, and notch filtering by changing its coefficients. This universal filter replaces what would traditionally require multiple dedicated filters, significantly reducing device complexity in both encoder and decoder while maintaining all necessary filtering capabilities

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The patent merges multiple filtering functions into a single configurable filter structure. By combining the functionality of what would be separate low pass, high pass, band pass, and notch filters into one adaptable filter with selectable coefficients, the patent reduces the overall device complexity and component count while preserving all required filtering operations

Inventive Principle:

Principle #5Merging (Combining)

Data Source

PatentUS7822210B2Configurable recursive digital filter for processing television audio signals

Publication Date: 2010.10.26 MIDDLESEX SAVINGS BANK

AI summary

A television audio signal encoder includes a device that sums a left channel audio signal and a right channel audio signal to produce a sum signal. The device also subtracts one of the left and right audio signals from the other to produce a difference signal. The encoder also includes a configurable infinite impulse response digital filter that selectively uses one or more sets of filter coefficients to filter the difference signal. The set of filter coefficients is applied to the difference signal by a single multiplier in a recursive manner to prepare the difference signal for transmission.