Kernel RAM Audio Buffering for Low Latency Playback
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Solution Overview
Problem
Android devices equipped with Push-To-Talk functionality experience high latency in playing the Talk-Permit-Tone, exceeding the desired 100 ms low latency specification, which is problematic for emergency responders due to longer initialization times for audio playback.
Innovation Solution
A device with a hardware digital signal processor (DSP) and dual audio paths, where digital audio samples are pre-loaded in kernel RAM buffers using a kernel driver, allowing for lower latency playback when available and higher latency playback when not, to minimize the duration from PTT key press to Talk-Permit-Tone playback.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If digital audio samples are loaded and played through the standard audio path, then the system maintains simplicity and reliability, but the playback latency exceeds the desired 100 ms specification
Solution Approach 1:
The audio playback system is segmented into two distinct paths: a standard audio path for normal operations and a low-latency audio path for time-critical operations. This segmentation allows the system to optimize for speed when needed without permanently increasing complexity for all operations.
Solution Approach 2:
Audio samples are pre-loaded into a dedicated low-latency buffer before they are needed for playback. This preliminary action ensures that when playback is triggered, the samples are already in memory and ready for immediate processing, eliminating the need for on-demand loading and reducing latency.
2Adaptability or versatility
If the system uses a single audio path, then the device complexity is minimized, but it cannot meet the low latency requirement for Push-To-Talk functionality
Solution Approach 1:
The audio playback system dynamically selects between two different audio paths based on the specific operational requirements. The controller determines whether to use the standard audio path or the low-latency audio path depending on whether time-critical performance is needed, making the system adaptable rather than static.
Solution Approach 2:
A dedicated low-latency buffer acts as an intermediary component between the audio sample storage and the digital signal processor. This intermediary structure enables fast playback by holding pre-loaded samples in a specialized buffer that can be quickly accessed by the DSP without going through the standard audio processing pipeline.
3Productivity
If audio samples are pre-loaded in kernel RAM buffers, then playback latency is reduced, but the system requires additional memory resources and complex buffer management
Solution Approach 1:
The low-latency buffer in kernel RAM serves multiple functions: it acts as a pre-loading storage area for audio samples, a quick-access buffer for the DSP during playback, and a management interface between the kernel driver and the audio processing system. This multi-functionality reduces the need for separate components while achieving low-latency performance.
Solution Approach 2:
The kernel driver automatically manages the pre-loading of audio samples into the low-latency buffer without requiring manual intervention or complex external control. The system self-regulates by monitoring when samples need to be loaded and performing the loading operation autonomously, simplifying the overall management complexity.
Data Source
AI summary
A device and method for lower latency digital audio sample playback is provided. The device comprises: a hardware digital signal processor (DSP); higher and lower latency audio paths to the DSP; a kernel driver; a kernel random-access memory (RAM) including kernel RAM buffers accessible by the kernel driver; and a controller. The controller: prior to digital audio samples being used by an application, pre-loads, using the kernel driver, the samples at the kernel RAM buffers; responsive to a trigger in the application to play a given digital audio sample, determines, using a sample identifier of the given sample, whether the given sample is pre-loaded at the kernel RAM buffers; when the sample is pre-loaded, plays, using the DSP, the given sample via the lower latency path; and when the given digital audio sample is not pre-loaded, plays, using the DSP, the given sample via the higher latency path.