Fidelity Defined
Fidelity. A word commonly used in consumer electronics ... But what does it mean?


fi•déli•ty n.  1. faithfulness; loyalty.  2. strict conformity to truth or fact.  3. exact correspondence to the original.  4. precision in reproduction of sound or video.

Background of the Accuracy Score
In the 1970s, Consumers Union used an "Accuracy Score" to rate loudspeakers. Consumer Reports reported that it is possible to predict listeners' loudspeaker ratings within 8% from a calculation based on one-third-octave frequency response measurements converted to loudness in sones. In short, their definition of Accuracy Score, as applied to loudspeakers was: the average error in loudness from a perfect system, subtracted from 100%.

In his doctoral dissertation, with permission from Consumers Union, Mead Killion expanded the 21-band accuracy score measure to a 25-band calculation, to determine frequency response accuracy of hearing aids. Since 1984, when Etymotic invented the first insert earphone, the 25-band accuracy score has been used in the design of all Etymotic earphones.

Accurate Earphone Reproduction
For earphones to have 100% accuracy, a recording of a live performance must produce exactly the same sound at the eardrum as the original performance. Sounds simple, but to achieve this, the acoustic properties of the ear must be factored in. The acoustic resonance and horn effects of the ear change a flat audio signal entering the open ear to sound (heard at the eardrum) that has a high frequency boost at approximately 2700 Hz in the typical ear canal.

A perfect earphone creates the same frequency characteristic at the eardrum.

Meet KEMAR®
The Knowles Manikin for Acoustic Research (KEMAR) has the same acoustic properties as the average head and ear. Originally developed for the hearing aid industry, it is now widely used in many areas of commercial audio and acoustic research. 

Target Curve Explained
Target curves on Etymotic frequency response accuracy graphs define 100% accuracy as the open ear diffuse-field response of the KEMAR manikin, modified to compensate for the high frequency boost added to high-quality recordings. This modification (approximately 5 dB at 10 kHz) is necessary to avoid earphones sounding too bright on commercial recordings. Commercial recordings have a high-frequency boost that compensates for the high frequency roll-off in studio monitor loudspeakers and high-quality stereo loudspeakers and earphones.

The 25-band accuracy calculation is used to measure all Etymotic and competing earphones. 25-band accuracy scores are calculated by summing the difference between the earphone response and the target response in each 1.3 -octave band from 50 Hz to 12.5 kHz. The accuracy scores of Etymotic earphones are higher than all competitive earphones, except electrostatic headphones that cost thousands of dollars. No other in-ear earphone manufacturer reports accuracy scores.