Audio Signal Compression Using Zero-Crossing Peak Scaling
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Solution Overview
Problem
Existing audio signal compression systems either introduce distortion by reducing signal levels too late or incur noise and inefficiency by not utilizing the full dynamic range, as they either clip signals or provide excessive headroom.
Innovation Solution
A method that identifies zero crossing points in audio signals to buffer and scale samples, ensuring the highest intensity samples do not exceed a threshold, using an initial scaling factor for the first half-wave and modified scaling factors for subsequent half-waves, with a decay factor to gradually return to normal scaling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the amplitude of the audio signal is measured and reduced when the peak exceeds a predetermined threshold, then distortion is prevented, but the procedure occurs too late and introduces distortion anyway
Solution Approach 1:
The patent applies preliminary action by measuring the amplitude of the audio signal in advance and comparing it with a predetermined threshold before the signal actually exceeds the threshold. This allows the system to take preventive scaling action ahead of time, ensuring that when the peak occurs, the signal has already been adjusted to prevent distortion. The key is performing the measurement and decision-making process early in the signal cycle rather than reacting after distortion has occurred.
2Reliability
If additional headroom is provided for the input signal to maintain a relatively low level, then peak values remain within dynamic range, but noise increases and efficiency decreases due to unavailable full dynamic range
Solution Approach 1:
The patent applies dynamics by making the scaling factor variable rather than fixed. The scaling factor is dynamically adjusted based on the measured amplitude of the input signal relative to a predetermined threshold. When the signal amplitude is low, minimal or no scaling is applied, preserving the full dynamic range and signal quality. When the amplitude approaches the threshold, the scaling factor increases automatically to prevent distortion. This dynamic adjustment eliminates the need for constant excessive headroom while still preventing peak distortion.
3Productivity
If the full dynamic range of the system is utilized, then efficiency is improved, but the risk of signal peaks exceeding the threshold and causing distortion increases
Solution Approach 1:
The patent applies feedback by continuously measuring the amplitude of the input signal and using this measurement to adjust the scaling factor in real-time. The measured amplitude feeds back into the scaling decision process, allowing the system to automatically adapt to the actual signal characteristics. This feedback mechanism enables the system to utilize the full dynamic range efficiently while maintaining distortion-free operation, as the scaling is precisely controlled based on actual signal levels rather than applying fixed conservative limits.
Data Source
AI summary
An audio signal in which an audio signal is received as a stream of digital samples, each being a numerical value representing a sampled signal level. A first zero crossing point is identified and the received audio samples are stored until a second zero crossing point is identified, thereby storing a first half-wave of samples. The highest intensity sample is identified from the stored samples and this is compared against a predetermined threshold. All stored samples are scaled by an initial scaling factor so that the intensity of the highest intensity sample is not above this threshold. A second half-wave of samples is stored in which all samples of the second half-wave are below the threshold. All stored samples of the second half-wave are also scaled but by a modified scaling factor derived from a combination of the initial scaling factor and a decay factor.