Test Tones

How the Test Tone Set works

A test tone is only useful if its level is known exactly. Here the level is set digitally: a peak of −20 dBFS means the sine's highest sample is exactly one tenth of full scale (10^(−20/20) = 0.1), and that is what the exported file contains.

Which test tones to use and at what level

1 kHz line-up. The workhorse. Send it through a chain and set every meter along the way to read the same. The two common reference levels are −20 dBFS (SMPTE RP 155, used in North American film and TV) and −18 dBFS (EBU R 68, used in European broadcast), each meant to line up with 0 VU or +4 dBu on analogue gear. That leaves 18–20 dB of headroom above the tone for programme peaks.

Left only and right only. The same 1 kHz tone on one channel at a time. Use them to prove the channels are not swapped anywhere between source and speaker, and that nothing is summing them to mono.

EBU stereo ident. A 1 kHz tone on both channels with the left channel cut for a quarter of a second every three seconds. The interruption tells you which side is which by ear, and if the channels are summed to mono the dropout becomes a small dip instead of silence.

440 Hz, 100 Hz, 10 kHz. A tuning reference, and a quick check of the low and high end of a chain: a lost 10 kHz tone points to a filter or a bad cable, a weak 100 Hz tone to a small speaker or a high-pass filter.

50 Hz and 60 Hz. The frequencies of mains electricity in most of the world and in North America. Play them to recognise the hum a ground loop makes, or to tune a notch filter to it.

Peak and RMS. Digital meters read peak; analogue VU meters respond to the average. For a sine the RMS level is 3.01 dB below the peak, which the panel shows, so a −20 dBFS peak tone reads −23 dBFS on an RMS meter. Some systems define their line-up level as RMS; check which your meter expects.

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