Delayed auditory feedback

Delayed auditory feedback (DAF), is a device that enables a user of the device to speak into a microphone and then hears his or her voice in headphones a fraction of a second later. Some DAF devices are hardware; DAF computer software is also available.

The DAF machine is a proven technique to aid with stuttering. When the DAF delay is short, (25 to 75 milliseconds, or about a twentieth of a second), this immediately reduces stuttering about 70%. A longer delay (75 to 200 milliseconds, or about tenth of a second) produces a greater increase in fluency, however it also causes significant reductions in rate of speech and stretched vowels. The longer delay is generally used in therapy settings. Some DAF devices have been found to produce carryover fluency, that is, to train a stutterer to no longer need the device.

DAF usage (with a 175 millisecond delay) has been proven to induce mental stress.

The DAF machine has also been claimed to be helpful with cluttering. The DAF machine reduces the rate of a clutterer, and thus reduces the cluttering disfluencies.