is SNR Loss?
SNR loss is the increased signal-to-noise ratio required by a listener to understand
speech in noise, as compared to normal performance. On the BKB-SIN Test
normal-hearing adults obtain 50% correct at a -2.5 dB SNR. We call this the
SNR-50. A hearing- impaired adult with an SNR-50 score of 7.5 dB would have a
10 dB SNR Loss [7.5 - (- 2.5) = 10]. The measurement of SNR loss is important
because it cannot be reliably predicted from the pure tone audiogram.
Performance on any speech-in-noise test is affected by a number of factors,
Due to these factors, absolute
scores for an individual subject will vary across different speech-in-noise
tests. BKB-SIN Test scores are reported in SNR Loss because it is substantially
independent of calibration and test material. Calibration and/or test material
differences that affect SNR-50 values equally for normal and hearing-impaired
listeners will "cancel out" in the SNR Loss calculation.
- Speech materials (sentences, spondees, etc.)
- Background noise (shaped noise, multi-talker babble)
- Test setup (combined speech and noise vs. separated speech and noise)
- Audibility of the signal
- Knowledge of the language
- Subject age
Knowing the SNR loss allows the hearing professional to recommend the appropriate
technology (e.g., omni-directional microphones, directional microphones, array
microphones, FM systems) required for the listener to function in noisy
situations. Knowing the SNR loss also enables the hearing professional to give
the patient realistic expectations for their potential improvement in noise
with a given technology, which often reduces unnecessary visits for hearing aid
re-adjustments after the fitting.
Interpreting test results for children should be done on a case-by-case basis.
Results should not be interpreted in isolation, but rather be integrated with
other information regarding a child's speech/language abilities, educational
performance and ability to function in the classroom. See "Test Interpretation
(children)" in the BKB-SIN Test manual for more information.