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In digital and analog audio, headroom refers to the amount by which the signal-handling capabilities of an audio system can exceed a designated nominal level. [1] Headroom can be thought of as a safety zone allowing transient audio peaks to exceed the nominal level without damaging the system or the audio signal, e.g., via clipping.
Some analog tape manufacturers specify frequency responses up to 20 kHz, but these measurements may have been made at lower signal levels. [16] Compact Cassettes may have a response extending up to 15 kHz at full (0 dB) recording level. [17] At lower levels (−10 dB), cassettes are typically limited to 20 kHz due to self-erasure of the tape media.
An extreme example, Todd Rundgren's Initiation LP, with 36 minutes of music on one side, has a "technical note" at the bottom of the inner sleeve: "if the sound does not seem loud enough on your system, try re-recording the music onto tape." The total of around 40–45 minutes often influences the arrangement of tracks, with the preferred ...
However, at high recording levels the treble output is further limited by saturation. At the Dolby recording level the upper frequency limit shrinks to a value between 8 kHz for a typical chromium dioxide tape, and 12 kHz for metal tapes; for chromium dioxide tapes, this is partially offset by lower hiss levels. [16]
Signal-to-noise ratio (SNR), however, is the ratio between the noise floor and an arbitrary reference level or alignment level. In "professional" recording equipment, this reference level is usually +4 dBu (IEC 60268-17), though sometimes 0 dBu (UK and Europe – EBU standard Alignment level).
Microphones, amplifiers and recording systems all add some electronic noise to the signals passing through them, generally described as hum, buzz or hiss. All buildings have low-level magnetic and electrostatic fields in and around them emanating from mains supply wiring, and these can induce hum into signal paths, typically 50 Hz or 60 Hz (depending on the country's electrical supply standard ...
Here, the still-mic-level signal enters into a microphone preamplifier, which boosts the signal voltage to line level. For this example, the microphone preamplifier is built into a mixing board. It is typical for a mixing board to include a line trim after the preamplifier. This allows the amplitude of the now line-level signal to be adjusted.
For example, CD audio uses 16 bits per sample, and therefore it will have quantization noise approximately 96 dB below the maximum possible sound pressure level (when summed over the full bandwidth) The amount of space required to store PCM depends on the number of bits per sample, the number of samples per second, and the number of channels.