See the piece I quoted regarding 'Auditory Masking' and 'Delayed Auditory Feedback (DAF)', or 'Frequency Altered Feedback'?

Develop a phone-app to use the phones' microphone to have adjustable delay, frequency-equalization and noise injection.

Find Bluetooth 'bone conduction headphones' that conducts through the collar-bone, these can be worn under a shirt.

Auditory Masking : https://en.wikipedia.org/wiki/Auditory_masking

Delayed Auditory Feedback (DAF) - Effects in People who Stutter : https://en.wikipedia.org/wiki/Delayed_auditory_feedback#Effe...

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