Crossfade Sample Playback Engine for Vehicle Engine Sound Simulation
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Solution Overview
Problem
Existing sound simulators for vehicle engines in virtual reality fail to accurately capture the variations in engine sounds due to load changes, resulting in unnatural sounds, as they neglect the dynamic changes in engine performance during acceleration and deceleration and incorrectly shift formants when pitching sound samples.
Innovation Solution
A vehicle engine sound simulator using a crossfade sample playback engine that transposes and mixes waveforms based on RPM, combined with a digital signal processing circuit that processes the output with a computed load value, incorporating both linear and nonlinear processing sections to simulate dynamic load effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If looped sound waves are used for engine sound simulation, then the basic engine sound can be reproduced, but the sound lacks variation according to load changes
Solution Approach 1:
The system dynamically adjusts the mixing ratio between different waveform samples based on the instantaneous load value. As load changes, the crossfade between samples continuously adapts, allowing the engine sound to reflect actual load conditions rather than remaining static.
Solution Approach 2:
The system changes the mixing ratio parameter dynamically based on load. By varying the proportion of different waveform samples according to the computed load value, the system achieves realistic load-dependent sound variation while maintaining the ability to reproduce basic engine sounds.
2Speed
If sound samples are pitched up and down to match RPM, then the engine speed variation can be simulated, but the formants shift unnaturally
Solution Approach 1:
The system segments the engine sound into multiple waveform samples, each captured at a specific RPM and load condition. By dividing the sound into discrete segments and selectively mixing them, the system avoids the need to pitch-shift single samples, thereby preserving formant accuracy while still simulating RPM variation.
Solution Approach 2:
Instead of transforming a single sample through pitch-shifting, the system creates multiple copies of the original recording at different RPMs and load conditions. These copies are then mixed according to the current operational state, preserving the authentic formants of each copy while achieving speed variation.
3Ease of manufacture
If steady-state vehicle sounds are recorded, then the basic engine characteristics can be captured, but the dynamic load variations during acceleration and deceleration are lost
Solution Approach 1:
The system uses a universal set of waveform samples that cover multiple load states (idle, acceleration, deceleration, steady-state). By designing the sample library to include diverse operational conditions, a single recording session can serve multiple functions, achieving comprehensive load state coverage without requiring separate recordings for each condition.
Solution Approach 2:
The system performs preliminary action by pre-recording waveform samples at various load states before actual simulation. This advance preparation creates a library of load-specific samples that can be quickly mixed during runtime, capturing dynamic load variations without requiring complex real-time recording during simulation.
Data Source
AI summary
A vehicle engine sound simulator includes a crossfade sample playback engine which produces an output waveform comprising at least two constituent waveforms which are transposed up and down in frequency with RPM. The playback engine's output waveform is provided to at least one digital signal processing (DSP) circuit, which processes the output with a function that varies with the rate of change of RPM, an external load value, and/or a combination of both to produce the simulator's output. The crossfade sample playback engine is arranged to crossfade between at least 2 wave samples as RPM changes. Wave samples from additional wave banks associated with different load states can also be mixed into the playback engine's output waveform. The DSP circuit can include both nonlinear and linear processing sections in various combinations.