Aircraft Digital Audio Side Tone Latency Management
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Solution Overview
Problem
Aircraft digital audio systems with latencies greater than 20 ms fail to provide reliable and timely side tone feedback, causing operators to hear their own voice with significant delay, leading to confusion during radio communication.
Innovation Solution
The system includes audio and radio terminals connected to a digital network, with a digital signal processor and message management units that generate and manage side tones, allowing activation/deactivation commands to be processed within 120 ms, ensuring side tone is received by the operator within 20 ms of transmission, using volume settings from the radio equipment's potentiometer and monitoring power levels in the transmission line.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the system uses high latency digital audio transmission (>20ms), then the digital network can manage multiple audio and radio equipment, but the operator hears his own voice with significant delay causing confusion
Solution Approach 1:
The system divides the audio feedback path into two independent segments: a fast local side tone path (microphone → audio terminal → headset) that provides immediate feedback within 20ms, and a separate digital transmission path (microphone → radio terminal → radio → headset) that handles long-distance communication. This segmentation allows the operator to hear their own voice immediately without waiting for the digital round-trip time.
Solution Approach 2:
The audio terminal acts as an intermediary device that generates and manages the side tone signal independently of the radio transmission status. It receives the microphone signal, generates the side tone, and sends it to the headset through a dedicated fast path, mediating between the microphone and headset to provide immediate feedback regardless of radio transmission latency.
2Ease of operation
If the side tone is generated locally at the audio terminal, then the operator hears voice with minimal delay (<20ms), but the system loses the ability to indicate transmission status through side tone absence
Solution Approach 1:
The system dynamically adjusts the side tone generation based on real-time transmission status. The audio terminal monitors the radio transmission state and activates or deactivates the side tone signal accordingly. When transmission is successful, the side tone is active; when transmission fails or is not possible, the side tone is deactivated. This dynamic behavior maintains the ability to indicate transmission status while preserving minimal latency feedback.
Solution Approach 2:
The system implements feedback mechanisms at multiple levels: immediate local feedback through the side tone path for transmission status indication, and separate feedback through the digital network for communication content. The audio terminal continuously monitors transmission conditions and adjusts side tone output accordingly, creating a closed-loop feedback system that maintains both latency performance and status indication reliability.
3Loss of time
If the activation command is received within 120ms, then the side tone can be activated in time for the current transmission, but there is still a waiting time that may affect real-time communication
Solution Approach 1:
The audio terminal continuously monitors the radio transmission status and prepares the side tone signal in advance. When transmission is detected as successful, the side tone is already generated and ready to be sent to the headset immediately, eliminating the need to wait for post-transmission processing. This preliminary preparation ensures that the side tone activation occurs within 120ms of transmission start, maintaining real-time communication efficiency.
Data Source
AI summary
A digital audio system of an aircraft comprising one or more pieces of audio equipment and one or more pieces of radio equipment providing a reliable side tone to the operators. The audio equipment and the radio equipment have installed in the proximity, respectively, an audio-terminal and a radio-terminal connected to a digital network including digital messages management units and digital signal processors. The digital messages management unit of the audio equipment is provided with a computer program adapted to generate a side tone of an analog audio message issued by the microphone of the audio equipment and to activate/deactivate its sending to the headset of the audio equipment when the audio-terminal receives from the radio-terminal an activation/deactivation command for said side tone.