Distortion Products analogy to the audiogram (Dpgram)


Distortion products are characterized by two stimulating sounds known as primaries. By varying the frequencies of these two primaries f1 and f2, it is possible to collect various distortion products to get a tracing called DPgram (graphic distortion products, analogy to the audiogram). By observing the spectrum cochlear, frequency by frequency (500Hz to 5 kHz), it is possible to estimate the degree of deafness.


User tips:

-       Make sure that the ear canal is not obstructed by a wax plug.

-       Patient must be settled comfortably to avoid any excessive muscle tension.

-       Check the right ear tip. It must not be pressed against a wall of the ear canal.

-       It must be hermetically sealed to prevent acoustic leaks and isolated from the noise.


Measure specifications:

-       1000 to 5000Hz

-       50 to 75dB SPL


Aimed Diseases:

-       Early detection of deafness in neonates.

-       Pediatric audiological evaluation.

-       Monitoring of sudden deafness.

-       Monitoring of professional and toxic deafness.



As part of the registration of acoustic distortion products (ADP), a bitonal acoustic stimulation is applied. This particular stimulus is going to put in movement two specific areas close to the cochlea and lead to the excitement of a third cochlear region. Made to vibrate the eardrum will emit a low amplitude but easily recordable and identifiable. For example, with the presentation of two primaries (f1 = 1000Hz and f2= 1200Hz), the distortion product 2f1-f2 is expected at 800Hz. The distortion product generated is lower frequency and lower amplitude than the primary. The amplitude of the distortion product which will be used as criterion for assessing cochlear function and more specifically the ECC of the emitter region (at a frequency of 800Hz in this example).

Thus, a distortion product with an amplitude greater than7 dB compared to the background noise will be the signature of the presence and operation of the ECC of the emitter region. The DP-gram is thus simple, quick to perform, reproducible and non invasive. The presence of the ADP confirms (in the absence of transmission deafness) the functioning of the cochlear ECC.


Echodia devices allowing  Dpgram measurements: ELIOS and OTODIA.