Erase Ratio
Erase ratio measures how far a tape recorder reduces a previously recorded signal, expressed in decibels.
A larger positive figure means less of the old signal remains under the stated test conditions. It describes erasure before a new recording, not the new recording's dynamic range or the machine's playback signal-to-noise ratio.
Erase Ratio — Cassette Deck
A cassette deck erases the previous recording as tape passes the erase head before being recorded again. The ratio indicates how effectively that old signal is suppressed. Tape formulation matters: a result stated for one cassette type should not be assumed to apply unchanged to another, particularly when metal tape is involved.
Compare the same test frequency and tape type, keeping any 'better than' qualifier attached to the value. Residual old audio is different from hiss or leakage between tracks. A playback-only cassette machine has no recording erase performance to compare, even if it can play previously recorded tapes.
Erase Ratio — Reel-to-Reel
On a reel-to-reel recorder, erase ratio indicates how thoroughly the previous programme is removed during recording. A faint surviving signal can be noticeable in quiet portions of the new programme, so the measurement addresses a different limitation from ordinary tape hiss. Its value belongs to the specified tape and operating conditions.
Compare results at the same test frequency and tape speed, and check whether the figures are exact values or lower limits. A higher number under a different test is not automatically a better result. Playback-only transports do not erase tape; their playback specifications cannot supply an erase-ratio figure.