Unsupervised Representation Learning Using Convolutional Restricted Boltzmann Machine for Spoof Speech Detection

Speech Synthesis (SS) and Voice Conversion (VC) presents a genuine risk of attacks for Automatic Speaker Verification (ASV) technology. In this paper, we use our recently proposed unsupervised filterbank learning technique using Convolutional Restricted Boltzmann Machine (ConvRBM) as a frontend feature representation. ConvRBM is trained on training subset of ASV spoof 2015 challenge database. Analyzing the filterbank trained on this dataset shows that ConvRBM learned more low-frequency subband filters compared to training on natural speech database such as TIMIT. The spoofing detection experiments were performed using Gaussian Mixture Models (GMM) as a back-end classifier. ConvRBM-based cepstral coefficients (ConvRBM-CC) perform better than hand crafted Mel Frequency Cepstral Coefficients (MFCC). On the evaluation set, ConvRBM-CC features give an absolute reduction of 4.76 % in Equal Error Rate (EER) compared to MFCC features. Specifically, ConvRBM-CC features significantly perform better in both known attacks (1.93 %) and unknown attacks (5.87 %) compared to MFCC features.