16. An article of manufacture including a non-transitory computer-readable storage medium, having stored thereon program instructions that, upon execution by one or more processors of a system, cause the system to perform operations comprising: transforming an input audio training signal into a sequence of feature vectors, wherein each feature vector of the sequence bears quantitative measures of acoustic properties of the input audio training signal; processing the sequence of feature vectors with an auto-encoder to generate (i) an encoded form of the quantitative measures, and (ii) a recovered form of the quantitative measures based on an inverse operation by the auto-encoder on the encoded form of the quantitative measures; processing a duplicate copy of the sequence of feature vectors with a normalizer to generate a normalized form of the quantitative measures in which supra-phonetic acoustic properties of the input audio training signal are reduced in comparison with phonetic acoustic properties of the input audio training signal; determining an error signal based on a difference between the normalized form of the quantitative measures and the recovered form of the quantitative measures; providing the error signal to the auto-encoder; and by adjusting parameters of the auto-encoder to reduce the magnitude of the error signal, training the auto-encoder to compensate for supra-phonetic acoustic properties of input audio signals.
16. An article of manufacture including a non-transitory computer-readable storage medium, having stored thereon program instructions that, upon execution by one or more processors of a system, cause the system to perform operations comprising: transforming an input audio training signal into a sequence of feature vectors, wherein each feature vector of the sequence bears quantitative measures of acoustic properties of the input audio training signal; processing the sequence of feature vectors with an auto-encoder to generate (i) an encoded form of the quantitative measures, and (ii) a recovered form of the quantitative measures based on an inverse operation by the auto-encoder on the encoded form of the quantitative measures; processing a duplicate copy of the sequence of feature vectors with a normalizer to generate a normalized form of the quantitative measures in which supra-phonetic acoustic properties of the input audio training signal are reduced in comparison with phonetic acoustic properties of the input audio training signal; determining an error signal based on a difference between the normalized form of the quantitative measures and the recovered form of the quantitative measures; providing the error signal to the auto-encoder; and by adjusting parameters of the auto-encoder to reduce the magnitude of the error signal, training the auto-encoder to compensate for supra-phonetic acoustic properties of input audio signals. 17. The article of manufacture of claim 16 , wherein the system comprises the auto-encoder and the normalizer, wherein the auto-encoder comprises a first sequential set of neural network layers adapted for forward processing of input, and a second sequential set of neural network layers adapted for inverse processing of input, and wherein processing the sequence of feature vectors with the auto-encoder comprises: forward processing the sequence of feature vectors with the first sequential set to generate the encoded form of the quantitative measures; and inverse processing the encoded form of the quantitative measures with the second sequential set to generate the recovered form of the quantitative measures.