Audio system measurements

Subjectively valid methods came to prominence in consumer audio in the UK and Europe in the 1970s, when the introduction of compact cassette tape, dbx and Dolby noise reduction techniques revealed the unsatisfactory nature of many basic engineering measurements.

[2] For these reasons, a set of subjectively valid measurement techniques have been devised and incorporated into BS, IEC, EBU and ITU standards.

Cassette noise, which was predominately high frequency and unavoidable given the small size and speed of the recorded track could be made subjectively much less important.

Note that digital systems do not suffer from many of these effects at a signal level, though the same processes occur in the circuitry since the data being handled is symbolic.

Digitizing adds noise, which is measurable and depends on the audio bit depth of the system, regardless of other quality issues.

Timing errors in sampling clocks (jitter) result in non-linear distortion (FM modulation) of the signal.

Regardless of the mix chosen, the FSK provides both identification and synchronization for each segment, so that sequence tests sent over networks and even satellite links are automatically responded to by measuring equipment.

Many audio components are tested for performance using objective and quantifiable measurements, e.g., THD, dynamic range and frequency response.

Some take the view that objective measurements are useful and often relate well to subjective performance, i.e., the sound quality as experienced by the listener.

[16] One of Toole's papers showed that objective measurements of loudspeaker performance match subjective evaluations in listening tests.

This does not imply that the defect is somehow unquantifiable or unmeasurable; just that a single THD number is inadequate to specify it and must be interpreted with care.

A number of formulas that attempt to correlate THD with actual audibility have been published, however, none have gained mainstream use.