  In this study, we propose a new concept, the gammachirp envelope distortion
index (GEDI), based on the signal-to-distortion ratio in the auditory envelope,
SDRenv to predict the intelligibility of speech enhanced by nonlinear
algorithms. The objective of GEDI is to calculate the distortion between
enhanced and clean-speech representations in the domain of a temporal envelope
extracted by the gammachirp auditory filterbank and modulation filterbank. We
also extend GEDI with multi-resolution analysis (mr-GEDI) to predict the speech
intelligibility of sounds under non-stationary noise conditions. We evaluate
GEDI in terms of speech intelligibility predictions of speech sounds enhanced
by a classic spectral subtraction and a Wiener filtering method. The
predictions are compared with human results for various signal-to-noise ratio
conditions with additive pink and babble noises. The results showed that
mr-GEDI predicted the intelligibility curves better than short-time objective
intelligibility (STOI) measure, extended-STOI (ESTOI) measure, and hearing-aid
speech perception index (HASPI) under pink-noise conditions, and better than
HASPI under babble-noise conditions. The mr-GEDI method does not present an
overestimation tendency and is considered a more conservative approach than
STOI and ESTOI. Therefore, the evaluation with mr-GEDI may provide additional
information in the development of speech enhancement algorithms.
