Alignment levels: dBFS, VU and dBu
Digital gear measures level in dBFS (decibels below full scale); analog gear in VU or dBu. The two are tied together by an alignment level: the dBFS value that a calibrated analog meter reads as 0 VU. Europe standardised on -18 dBFS, the US on -20 dBFS. Pick the one your destination expects and the tone will read 0 VU there.
| Digital | Analog | Used for |
|---|---|---|
| 0 dBFS | Clipping point | Never for line-up. Only to verify a chain passes full scale cleanly. |
| -6 dBFS | - | Casual speaker checks, tone downloads. Loud but with headroom. |
| -12 dBFS | - | Comfortable listening checks, headphones. |
| -18 dBFS | 0 VU / +4 dBu | EBU R68 alignment level. European broadcast, most DAW nominal levels, Pro Tools default. |
| -20 dBFS | 0 VU / +4 dBu | SMPTE RP 155 alignment level. US broadcast, film post, Dolby. |
How to line up a system with 1 kHz
- 1
Select 1 kHz at your alignment level
Choose the 1 kHz preset and set the level to -18 dBFS (EBU) or -20 dBFS (SMPTE) - whichever standard the destination expects. Leave routing on Left + Right.
- 2
Set your output to unity
Put the computer or device volume at 100% (or 0 dB) so the tone leaves at exactly the level shown. Any volume control between this page and the destination becomes part of the chain you are calibrating.
- 3
Read the meter at the destination
On the interface input, mixer channel, recorder or broadcast chain, the tone should read 0 VU on an analog meter or the same dBFS value on a digital one.
- 4
Adjust the destination gain only
Trim the input gain at the receiving end until the meter reads the reference. Do not touch the source level - the point of a line-up is that the source is known.
- 5
Check each channel
Switch routing to Left only, then Right only, and confirm both meters read the same. A mismatch here is a channel gain or wiring issue, not a source issue.
Speaker, wiring and room checks
Which speaker is which: play 440 Hz with routing on Left only, then Right only. If the wrong speaker answers, the cables are swapped at the amp or the receiver. The speaker balance test pans continuously if you want a finer check.
Polarity: play 100 Hz with Right inverted and stand centred between the speakers. Correct wiring cancels the bass and sounds thin and hollow; if Right inverted sounds fuller than Left + Right, one speaker's + and - are reversed. The speaker phase test walks through it step by step.
Dropouts, resonances and rattles: run the 20 Hz-20 kHz sweep at -12 dBFS and listen for frequencies that vanish, boom, or buzz. The bass sweep does the same for the octaves where room modes live - the room mode calculator tells you which frequencies to expect. For a deeper bass check use the subwoofer test.
Level matching: pink noise at -20 dBFS through each speaker in turn, SPL meter on C-weighting / slow at the listening position, trim each channel until they read the same. Home theatre receivers do exactly this in their auto-setup.
Generator, downloads, or any frequency?
This page plays a fixed set of reference signals at a precise level - for calibration and checks. If you need files to carry to another device, the test tone downloads page renders the same catalog as WAV or MP3 up to three minutes long. If you need a specific frequency rather than a reference, the tone generator plays anything from 20 Hz to 20 kHz, and the sweep generator lets you set sweep range and speed yourself. The 1 kHz page goes deeper on why that frequency is the reference.