Trill Encoding Modules for Alveolar Trill Intelligibility
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Solution Overview
Problem
Digital land mobile radios often distort speech sounds like the alveolar trill, particularly in languages such as Spanish and Italian, due to the low frame energy analysis rate of narrowband vocoders, leading to reduced intelligibility.
Innovation Solution
A parallel and post-processing approach is implemented using trill encoding and decoding modules within the transmit and receive radios to enhance the modulation index of speech sounds, specifically the alveolar trill, by detecting trill nulls and coding trill information into additional bits, which are then used to reshape the waveform at the output of the vocoder decoder.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If narrowband vocoders are used in digital land mobile radios, then the speech signal can be converted to digital format and transmitted, but the alveolar trill sounds become distorted and smeared due to low frame energy analysis rate
Solution Approach 1:
The patent segments the speech signal processing into two independent paths: the standard narrowband vocoder path for general speech transmission, and a parallel trill enhancement path that specifically processes trill sounds. The trill detector identifies trill segments, and the trill synthesizer reconstructs them with enhanced fidelity. This segmentation allows the system to maintain reliable speech transmission while improving trill sound precision without modifying the standard vocoder.
Solution Approach 2:
The patent introduces intermediary components (trill detector and trill synthesizer) that act as mediators between the vocoder input and output. The trill detector intercepts the speech signal to identify trill portions, and the trill synthesizer inserts enhanced trill waveforms back into the signal stream. These intermediaries enable trill enhancement without altering the core vocoder operation, resolving the contradiction between reliable transmission and high fidelity.
2Manufacturing precision
If the vocoder's frame analysis rate is increased to improve trill encoding accuracy, then the modulation index of trill sounds improves, but the bit rate and processing complexity increase
Solution Approach 1:
The patent applies local quality enhancement by focusing computational resources only on trill sound segments rather than processing the entire speech signal at high resolution. The trill detector identifies specific time intervals containing trills, and the trill synthesizer applies enhanced waveform generation only during these intervals. This localized approach improves trill encoding accuracy without increasing the overall frame analysis rate or processing complexity of the vocoder.
Solution Approach 2:
The patent changes parameters locally for trill segments by switching from the vocoder's standard low-frame-rate parameter encoding to a high-resolution waveform synthesis mode. The trill synthesizer generates waveforms with accurate modulation indices by directly controlling amplitude and frequency parameters during detected trill intervals. This parameter change is applied only when needed, avoiding the complexity of increasing the global frame analysis rate.
3Loss of information
If additional processing modules are added to detect and encode trill information, then the intelligibility of trill sounds improves, but the device complexity increases
Solution Approach 1:
The trill detector performs preliminary action by identifying and flagging trill segments in the speech signal before the vocoder processes them. This early detection allows the system to prepare enhanced trill waveforms in advance, ensuring that trill information is preserved without requiring complex real-time processing during vocoder operation. The preliminary detection simplifies the overall system architecture by separating detection from synthesis.
Solution Approach 2:
The trill synthesizer creates a copy of the detected trill waveform with enhanced quality and inserts it back into the speech signal. Rather than attempting to modify the vocoder's core encoding process, the system generates a separate, high-fidelity copy of the trill portion and combines it with the vocoder output. This copying approach preserves trill information effectively while keeping the processing modules relatively simple and independent.
Data Source
AI summary
A method and apparatus for enhancing audio processing between a transmit radio (230) and a receive radio (240) are provided. Digitized audio frames (202) are applied to parallel inputs of both a vocoder encoder (204) and a trill encoder 212 of the transmit radio (230). The vocoder encoder (204) generates voice bits which are communicated over a voice bits channel (206) to a vocoder decoder (208) of the receive radio (240). Trill encoder (212) generates signaling bits which are communicated over a signaling bits channel (214) to a trill decoder (216) of the receive radio (240) for recovery of trill information (218). At the receive radio (240), a decoded audio signal (209) generated from the vocoder decoder (208), and the recovered trill information (218) are both provided as inputs to a trill reconstructor stage (220) to generate a recovered audio signal (222) having a reconstructed trill.