VU meters track average level (close to perceived loudness); peak meters track instantaneous peaks, 10–25 dB higher

A VU (Volume Units) meter has ballistic characteristics — a defined needle time-constant — that make it follow average program level and ‘look’ at the signal closer to the way we hear, giving a more accurate indication of relative loudness. A peak meter (PPM) responds to instantaneous peaks with fast attack and slow decay. For typical program material the instantaneous peak exceeds the VU reading by 10–25 dB, which matters for gain staging: setting a track to read 0 VU leaves 10–25 dB of headroom that must be accommodated before clipping, since clipping and digital overs occur at instantaneous peaks, not at average level. The two are complementary. A quiet voice with a high transient peak can ‘look’ loud on a peak meter yet sound quiet; a VU reveals perceived-loudness differences a peak meter hides — but a VU lacks the precision to catch peaks and overs. So engineers use both: peak meters for overs, VU-style metering for perceived loudness. Some meters show both ballistics at once.

Examples

Two songs both peaking at 0 dBFS can differ audibly in loudness; a VU exposes the difference a peak meter hides, so when matching songs across an album you trust perceived level (ear plus VU). A console reading +3 VU with a +20 dBu clip point still has headroom — but the true peaks sit 10–25 dB above the VU reading, so check a peak meter before assuming safety.

Assessment

Why is a VU meter more useful than a peak meter when matching perceived loudness between songs, and what is its weakness? A console VU reads +3 VU and clips at +20 dBu — is there clipping risk? Explain using the VU-to-peak relationship.