Flexible Polyphase Rate Conversion With Coefficient Interpolation
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Solution Overview
Problem
Traditional rate conversion methods, including poly-phase filters, face challenges such as high computational complexity, inflexibility, and resource-intensive requirements, especially when converting between incommensurate sampling rates like 44.1 kHz and 48 kHz, which demands a large number of filter coefficients and operates at high sampling rates, making them inefficient and costly.
Innovation Solution
A flexible poly-phase filter structure that adjusts filter coefficients based on the phase index, allowing for interpolation between nearby phase indices, and using multiple poly-phase subfilters with interpolation and small fraction approximation techniques to reduce computational load and storage requirements, enabling efficient rate conversion across varying sampling rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If traditional rate conversion methods are used to convert between incommensurate sampling rates (e.g., 44.1 kHz to 48 kHz), then the conversion can be achieved, but the computational complexity and resource demands become excessively high
Solution Approach 1:
The patent divides the rate conversion process into multiple poly-phase subfilters, each handling a specific phase of the conversion. This segmentation allows the complex conversion between incommensurate sampling rates to be broken down into manageable stages, reducing the computational burden on any single processing element while maintaining overall conversion capability.
Solution Approach 2:
The patent implements variable rate conversion by dynamically adjusting the operating rate of poly-phase subfilters based on the specific conversion ratio required. Instead of always operating at the maximum common multiple rate, the system adapts the processing rate to match the actual conversion needs, significantly reducing computational complexity when converting between incommensurate sampling rates.
2Manufacturing precision
If traditional poly-phase filters are used for rate conversion, then filtering can be performed, but the filter must operate at high sampling rates requiring thousands of coefficients
Solution Approach 1:
The patent uses variable rate poly-phase subfilters that dynamically adjust their operating rate based on the conversion ratio. This allows the filter to maintain high filtering accuracy by using sufficient coefficients only when needed, while operating at lower effective rates for common conversions, thereby reducing the average number of coefficients required in the system.
Solution Approach 2:
The patent changes the operating parameter (sampling rate) of the poly-phase subfilters dynamically based on the conversion ratio. By adjusting the operating rate parameter, the system can achieve accurate filtering with fewer coefficients for typical conversions, reducing the overall quantity of coefficients needed while maintaining filtering precision.
3Adaptability or versatility
If a least common multiple approach is used for rate conversion, then the conversion can be achieved, but the intermediate sampling rate becomes excessively high
Solution Approach 1:
The patent implements variable rate poly-phase subfilters that adapt their operating rate to the specific conversion ratio required. Instead of always using the high least common multiple rate, the system dynamically selects an appropriate intermediate rate that is sufficient for the conversion task, thereby reducing the intermediate sampling rate and associated computational burden.
Solution Approach 2:
The patent changes the intermediate sampling rate parameter based on the conversion ratio being performed. By adjusting this parameter dynamically, the system avoids using excessively high intermediate rates for simple conversions, reducing the speed requirements while maintaining the ability to handle any conversion ratio including incommensurate rates.
Data Source
AI summary
Poly-phase filters are used to offer an efficient and low complexity solution to rate conversion. However, they suffer from inflexibility and are not easily reconfigured. A novel design for rate converters employ poly-phase filters but utilize interpolation between filter coefficients to add flexibility to rate conversion. This interpolation can be implemented as an interpolation of the poly-phase filter results. Additional approximations can be made to further reduce the amount of calculations required to implement a flexible rate converter.