Remember: Cross hearing is Bone-Conduction mechanism AC: in Supra aural  IA = 40 in insert earphone  75 dB ≤ 1000 50 dB > 1000 BC: IA = 0

for all threshold & suprathreshold speech measurements in Supra-aural earphone IA = 40 (WDS) & 45(SRT) dB in 3A insert earphone

IA = 60 dB

When to mask? AC:  ACte – BCnte ≥ IA

or

SRT:  SRTte – BCnte ≥ IA

or

ACte -ACnte SRTte – SRTnte

WDS:  PLte – Best BCnte Minimum Masking Level AC: Initial masking level= ACnte + 10 dB = … dB EM BC: Initial masking level= ACnte + OE + 10 dB = … dB EM

SAL test: AC1 in quiet AC2 in noise generated by bone vibrator NBN AC2 – SaL norm = X dB X = ABG (air-bone gap)

Maximum Masking Level: AC & BC :  BCte + IA – 5 dB Plateau method: 1- unmasked ACte – unmasked ACnte ≥ IA 2- initial masking level  unmasked ACnte + 10  Re-test TE  if shifted add another 10 to NTE  if shifted add another 10 dB to NTE if NOT shifted  add another 10 to NTE we search for 3 successive increament in NTE with fixed threshold in TE  this is plateau  value of masking at which fixed threshold begins = Minimal masking level or changeover point below which under masking & last value of fixation called Maximum Masking Level above which overmasking occurs *** Some prefer step size 5 dB instead of 10 dB. Step Masking

No threshold shift  √√

AC & SRT: Initial masking level = ACnte + 30 dB EM

Threshold shifted by ≥ 20 dB  Subsequent masking by adding 20 dB EML above previous masking level no shift √√  threshold shifted  another round of subsequent masking.

BC: Initial masking level = ACnte + 20 dB EM + OE  No threshold shift  √√

OR

Threshold shifted by ≥ 15 dB  Subsequent masking by adding 15 dB EML above previous masking level  no shift √√  threshold shifted  another round of subsequent masking.

For AC

For BC:

Min = ACte -IA + ABGnte

Min = BCte + ABGnte

Max= BCte + IA

Max = BCte + IA

For SRT masking:

For WRS:

EML = SRTte – IA + ABGnte EML = PLte – IA + ABGnte

Formula Computation Method

For other special test e.g. Tone decay  EML = BCte + IA – 5 dB