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Fmp and Residual Noise

What is Residual Noise?

  •  It is the averaged background noise.

    How does it Work?
  • It is calculated online during the ABR recording by measuring the stability of the averaged waveform.
  • The residual noise calculation used for Fmp is the same used for the calculation of Residual Noise - typically in a time window of 10ms.
  • The greater the stability, the less noise in the tracing.
  • When the Residual Noise level reaches the set criteria, e.g. 40nV for adults and 20nV for children, the residual noise bar turns green with a checkmark.

What is Fmp?

  • It is a statistical online analysis of the ABR recording from beginning to end.
  • The Response Confidence is a statistical confidence of a true detection of a response, by default 99% (Fmp 3.1).

    How does it Work?
  • It works on the principle of comparing response amplitude to residual noise to provide confidence level or detection rate.
  • The underlying analysis considers the ABR recording typically in a time window of 10ms.
  • The Fmp ratio between the response amplitude and the residual noise is calculated.
  • In a response situation, lower noise or larger response amplitude will drive the Fmp up (indicated by the red line and bar).
  • In a no-response situation, the response amplitude will not rise above the residual noise, thus the Fmp value and the Response Confidence will remain low.

    What is the benefit of calculating Fmp?
  • The calculation provides statistical documentation and support of the findings.
  • Acts as a Quality Meter for the waveform.

Benefits of Fmp and Residual Noise

  • Low residual noise levels mean there is less noise in the tracing.
  • Less noise in the tracing improves confidence when eyeballing the presence or absence of a response.
  • It is unlikely that continued averaging with noise levels below 40nV for adults and 20nV for children will result in a response becoming visible, so residual noise may be used as stop criteria in no-response situations.

Clinical benefits

  • Improves confidence in a presence or absence of the response.
  • Can reduce test time.
  • Relies on statistical data not solely on the experience of the user in determining the presence or absence of the response.

References 
Don, M. & Elberling, C. (1996). Use of quantitative measures of auditory brain-stem response peak amplitude and residual background noise in the decision to stop averaging. J. Acoust. Soc. Am., 99(1).

Elberling, C. & Don, M. (1984). Quality Estimation of averaged auditory brainstem responses. Scand Audiol., (13) 187-197.

July 2016
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