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Fletcher’s band-widening experiment (1940)

Fletcher’s band-widening experiment (1940). Present a pure tone in the presence of a broadband noise. Both signal and noise are presented simultaneously . Signal is kept constant (in frequency and intensity). Bandwidth of the noise is increased, keeping spectrum level constant. Power.

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Fletcher’s band-widening experiment (1940)

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  1. Fletcher’s band-widening experiment (1940) • Present a pure tone in the presence of a broadband noise. • Both signal and noise are presented simultaneously. • Signal is kept constant (in frequency and intensity). • Bandwidth of the noise is increased, keeping spectrum level constant.

  2. Power Frequency (Hz) Noise spectrum Signal

  3. Masked signal threshold Bandwidth of masker Concept of the critical bandwidth • Results: At first, the masked threshold of the signal increased. After a certain bandwidth, no more change in the signal threshold. • This bandwidth was termed the critical bandwidth. Critical bandwidth

  4. Explanation of results • Theory: Bandpass ‘internal’ filter centered around signal frequency. • Both signal and the noise passed through this bandpass filter. • Only the bandwidth of the noise that passes through the internal filter has an effect on the signal threshold. • Beyond this point, noise only increases in loudness.

  5. Power Frequency (Hz) Internal filter Noise spectrum Signal

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