The EBU Specification for 5.1 line-up tones is shown in the diagram.
All the five main channels have 3 seconds of 1 kHz tone, followed by a 0.5 second silence, following which they are identified in clockwise order beginning at front left by a 0.5 second burst of tone followed by a 0.5 second silence before the 0.5 second tone on the next channel and so on. The LFE channel is identified by having continuous 80 Hz tone. It should be noted that although this is recorded at line-up level, the LFE channel is usually reproduced 10 dB higher in level, but the lower perceived loudness of the 80 Hz tone ensures an even balance is maintained.
The specification allows for expansion of this scheme by adding the extra channel ident bursts at the appropiate time whilst maintaining the clockwise sequence.
See also BLITS.