A major factor influencing the performance in speaker recognition is speech quality, in particular the bandwidth of the recording, the location of the speech acquisition system (anechoic chamber , studio , office, street, ...), the type of microphone used, and the transmission channel (direct recording, telephone transmission, radio transmission, type of signal coding, ...).
In practice, it is essential that the description of speech quality reports accurately the general characteristics, but also underlines what the variable factors and those that remain constant are between several trials of the same user.
For instance, speaker recognition through the telephone is generally more difficult than speaker recognition using studio recordings. But two evaluations using telephone speech may give different results if for the first one each speaker always calls from the same place using the same telephone, while for the second one he is asked to call from different locations. Naturally, the latter is likely to give better results than the former.