hardScenarioDesignSeniorStaff
How do you optimise an FIR filter implementation on a resource-constrained DSP for ultra-low-latency active noise cancellation?
2 min readUpdated 2026-08-15
Answer
Short answer
Evaluate the candidate's proficiency in implementing and optimising digital signal processing algorithms on hardware, focusing on FIR/IIR trade-offs, fixed-point arithmetic, and instruction-level parallelism.
Active Noise Cancelling (ANC) audio pipelines demand ruthless optimization. Processing feedforward and feedback microphone signals to generate an anti-noise waveform on an ultra-low-power Digital Signal Processor (DSP) leaves zero margin for latency. The control loop dictates a strict group delay limit—often under 10 microseconds. Exceeding this budget misaligns the anti-noise with ambient sound, causing catastrophic constructive interference that actively amplifies the noise.
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Likely follow-ups
- How would your filter design change if the ANC system needed to support multiple simultaneous frequency bands with different phase requirements?
- What happens to your fixed-point scaling strategy if the microphone's dynamic range increases unexpectedly under loud transient noise?
- How do you validate that your biquad cascade remains numerically stable across the full temperature range the DSP will operate in?
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