Setting a car amplifier’s gain? Don’t use this −20 dBFS file: use the 0 dBFS tone on the amp gain test tones page, which also has the steps and target voltages.
What a 1 kHz tone is for
A steady 1 kHz sine at a known level is the standard line-up signal in audio. Recorded at the head of a programme, it lets whoever plays the file next set their meters so the programme arrives at the level it was mixed at. Played into an interface, a mixer or a recorder, it shows whether every stage in the chain passes the signal at the level you expect. And because the A-weighting used by sound level meters is defined as 0 dB at 1 kHz, a 1 kHz tone reads the same on a meter with or without that weighting.
Reference levels
| Standard | Where it’s used | Digital level | Analog level |
|---|---|---|---|
| SMPTE RP 155 | American television | −20 dBFS | +4 dBu (1.228 V RMS) |
| EBU R 68 | European broadcasting | −18 dBFS | 0 dBu (0.775 V RMS) |
EBU R 68 itself defines only the digital level: alignment level 18 dB below the maximum level a digital system can code, whatever its bit depth. The analog equivalents in the table are common line-up practice rather than part of R 68; the dBu figures are voltages relative to 0.775 V.
How to line up with the tone
- The page opens on 1,000 Hz with the download set to a 60-second WAV at −20 dBFS and 48 kHz. For EBU work, choose −18 dBFS under Peak level; for a different delivery spec, pick its level.
- Download the file and place it at the start of your timeline or play it through the chain you are checking.
- Read the meters. A peak meter shows the level you chose; a plain RMS meter shows about 3 dB less. On analog gear lined up to SMPTE, −20 dBFS should read +4 dBu.
The level is exact only in the downloaded file. This page’s Play button and tone buttons play at the Volume slider’s setting, so use them to hear the tone, not to line up.
Video editors can generate bars and tone inside their software as well: Adobe’s help for Premiere Pro explains how to change its tone’s level with Clip > Audio Options > Audio Gain. A file made here has its level fixed in the file itself, so it arrives at the same level in any editor or player.
997 Hz and 1004 Hz
Two close neighbours of 1 kHz exist for technical reasons. 997 Hz is the frequency the AES17 standard uses to define full scale and to test digital audio equipment: unlike 1000 Hz, it doesn’t fit a whole number of cycles into the common sample rates, so the test exercises many more of the converter’s values. 1004 Hz is the telephone test tone, offset from 1000 Hz to avoid effects that some carrier equipment has on test tones.
To check left and right speaker channels, use the speaker test, and for any other frequency the tone generator.