Audio Rate Converter with Anti-Alias Interpolation and Gated Clock
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Solution Overview
Problem
Conventional rate converters face challenges in producing output signals with high Signal-to-Noise Ratio (SNR) and flat frequency response, particularly in audio signals, due to aliasing issues during resampling.
Innovation Solution
A rate converter design with a 6-channel forward path and 2-channel reverse path, utilizing a gated clock in low-power mode, featuring a conversion rate tracking loop with a simple 1st order IIR filter and sample interpolator with 3rd order polynomial approximation for anti-alias filters, ensuring high SNR and efficient power usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional rate converters use standard resampling methods, then the device complexity is reduced, but the Signal-to-Noise Ratio (SNR) and frequency response flatness deteriorate due to aliasing
Solution Approach 1:
The rate converter is divided into multiple independent channels (6 forward channels, 2 reverse channels), each with dedicated 24-bit or 16-bit signal paths. This segmentation allows parallel processing of multiple audio streams simultaneously while maintaining high SNR (110 dB for audio, 93 dB for voice) through dedicated filtering and interpolation resources per channel.
Solution Approach 2:
Anti-alias filtering is performed before the resampling operation in the conversion rate tracking loop. The system pre-calculates the required filter coefficients and applies them to the input signal before downsampling or rate conversion, preventing aliasing artifacts from being introduced during the resampling process. This preliminary filtering action ensures high frequency response flatness across the 20 Hz to 20 KHz audio bandwidth.
2Measurement precision
If conventional rate converters operate continuously to maintain high performance, then the SNR is maintained, but the power consumption increases
Solution Approach 1:
The rate converter implements a gated clock mechanism that periodically activates computation blocks only when rate conversion is actually needed. The conversion rate tracking loop and sample interpolators are enabled during active audio processing intervals and disabled during idle periods, reducing power consumption while maintaining 110 dB SNR performance when operational. This periodic activation is particularly effective for reverse path voice signals where processing can be selectively applied.
Solution Approach 2:
The system dynamically adjusts the operational state of different computation blocks based on real-time processing requirements. The gated clock selectively enables or disables specific channels and processing stages (anti-alias filtering, interpolation, resampling) depending on the current audio stream characteristics and power management needs, optimizing the balance between SNR performance and power consumption.
Data Source
AI summary
Embodiments of the invention may be used to implement a rate converter that includes: 6 channels in forward (audio) path, each channel having a 24-bit signal path per channel, an End-to-end SNR of 110 dB, all within the 20 Hz to 20 KHz bandwidth. Embodiment may also be used to implement a rate converter having: 2 channels in a reverse path, such as for voice signals, 16-bit signal path per channel, an End-to-end SNR of 93 dB, all within 20 Hz to 20 KHz bandwidth. The rate converter may include sample rates such as 8, 11.025, 12, 16, 22.05, 24, 32 44.1, 48, and 96 KHz. Further, rate converters according to embodiments may include a gated clock in low-power mode to conserve power.