PCT No. PCT/FI95/00667 Sec. 371 Date Aug. 11, 1997 Sec. 102(e) Date Aug. 11, 1997 PCT Filed Dec. 5, 1995 PCT Pub. No. WO96/18251 PCT Pub. Date Jun. 13, 1996When several successive bad frames are received, a speech signal applied to an audio speaker is muted after a certain period of time, whereby the user may switch the phone off even though it is possible for the transmission channel to regain its good quality. Instead of the muting of the phone, the user is, according to the invention, given a specific indication, a weak noise signal, for example, indicating that the call synthesization has been discontinued on purpose. The noise signal may be generated in a noise generator prior to a speech decoder, and the noise signal is summed with the attenuated parameter values of the frames substituted during subsitution process.
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