title: The effect of notch filtering on the waveform of the newborn auditory brainstem response.
abstract: OBJECTIVE
  To identify whether the use of a notch filter significantly affects the morphology or characteristics of the newborn auditory brainstem response (ABR) waveform and so inform future guidance for clinical practice.
  
  
  METHODS
  Waveforms with and without the application of a notch filter were recorded from babies undergoing routine ABR tests at 4000, 1000 and 500 Hz. Any change in response morphology was judged subjectively. Response latency, amplitude, and measurements of response quality and residual noise were noted. An ABR simulator was also used to assess the effect of notch filtering in conditions of low and high mains interference.
  
  
  RESULTS
  The use of a notch filter changed waveform morphology for 500 Hz stimuli only in 15% of tests in newborns. Residual noise was lower when 4000 Hz stimuli were used. Response latency, amplitude, and quality were unaffected regardless of stimulus frequency. Tests with the ABR stimulator suggest that these findings can be extended to conditions of high level mains interference.
  
  
  CONCLUSIONS
  A notch filter should be avoided when testing at 500 Hz, but at higher frequencies appears to carry no penalty.
authors.affiliation: * Department of Medical Physics & Clinical Engineering, Royal Liverpool University Hospital , Liverpool , UK.
authors.forename: Guy
authors.initials: G
authors.lastname: Lightfoot
authors.forename: Inga
authors.initials: I
authors.lastname: Ferm
authors.forename: Amanda
authors.initials: A
authors.lastname: Hall
authors.forename: Kathryn
authors.initials: K
authors.lastname: Evans
mesh_terms: D000161:Acoustic Stimulation; D001306:Auditory Pathways / Q000502:physiology*; D001309:Auditory Threshold; D016057:Evoked Potentials, Auditory, Brain Stem; D006320:Hearing Tests; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D015997:Neonatal Screening / Q000379:methods; D011930:Reaction Time; D012815:Signal Processing, Computer-Assisted; D013018:Sound Spectrography; D013997:Time Factors
keywords: Auditory brainstem response; distortion; notch filter