Analysis and on-line detection of audible distortions in GSM telephony

Channel errors significantly impair the quality of GSM transmitted speech. In this contribution, we first analyze the speech distortions caused by error control failures or due to the basic frame substitution technique used by the GSM Full Rate. In particular, we show how this frame substitution procedure may introduce frame rate harmonics in the speech spectrum. Then we present algorithms that perform on the decoded speech in order to detect and conceal these distortions. The frame rate harmonics are detected by comparing a 50 Hz periodicity measure to a pitch estimate. The distortions due to Cyclic Redundancy Check (CRC) failures are detected by exploiting time and mutual correlation of speech parameters. These algorithms are optimized in order to reduce false alarms.