Editing Audio system measurements (section)

=== Analog electrical ===
; [[Frequency response]] 
: This measurement tells you over what frequency range output level for an audio component will remain reasonably constant (either within a specified [[decibel]] range or with reference to amplitude at 1&nbsp;kHz). [[Preamplifiers]] may also contain [[equalization (audio)|equalizer]]s for example to play [[LP album|LP]]s requiring [[RIAA_equalization|RIAA frequency response correction]], in which case the specification may describe how closely the response matches the standard. On the other hand, [[frequency range]] is a term sometimes used of [[loudspeakers]] and other [[transducers]] to indicate the frequencies that are usable, without necessarily specifying a decibel range.  [[Power bandwidth]] is also related to frequency response{{snd}}indicating the range of frequencies usable at high power.
: A component having a ''flat'' frequency response will reproduce content at all frequencies across the specified frequency range at the same intensity. The frequency range often specified for audio components is between {{val|20|u=Hz}} to 20&nbsp;kHz, which broadly reflects the [[human hearing range]]. Well-designed solid-state amplifiers and CD players may have a frequency response that varies by only 0.2&nbsp;dB between 20&nbsp;Hz to 20&nbsp;kHz.<ref>Metzler, Bob, [http://ap.com/download/books "Audio Measurement Handbook"] {{webarchive |url=https://web.archive.org/web/20090621184958/http://ap.com/download/books |date=21 June 2009 }}, Second edition for PDF. Page 86 and 138. Audio Precision, USA. Retrieved 9 March 2008.</ref> Loudspeakers tend to have considerably less flat frequency responses than this.

; [[Total harmonic distortion]] (THD) 
: Music material contains distinct tones, and some types of distortion involve spurious tones at double or triple the frequencies of those tones. Such harmonically related distortion is called harmonic distortion. For [[high fidelity]], this is usually expected to be <1% for electronic devices; mechanical elements such as loudspeakers usually have inescapable higher levels. Low distortion is relatively easy to achieve in electronics with use of [[negative feedback]], but the use of high levels of feedback in this manner has been the topic of controversy among [[audiophile]]s.<ref>{{cite web |url=https://www.passlabs.com/technical_article/audio-distortion-and-feedback/ |title=Audio distortion and feedback |access-date=2025-02-17 |author=Nelson Pass}}</ref> Essentially all loudspeakers produce more distortion than electronics, and 1–5% distortion is not unheard of at moderately loud listening levels. Human ears are less sensitive to distortion in the low frequencies, and levels are usually expected to be under 10% at loud playback. Distortion that creates only even-order harmonics for a sine wave input is sometimes considered less intrusive than odd-order distortion.

; [[Audio power|Output power]] 
: Output power for amplifiers is ideally measured and quoted as maximum [[root mean square]] (RMS) [[power (physics)|power]] output per channel, at a specified distortion level at a particular load, which, by convention and government regulation, is considered the most meaningful measure of power available on music signals.
: Power specifications require the [[load impedance]] to be specified, and in some cases, two figures will be given (for instance, the output power of a power amplifier for loudspeakers will be typically measured at 4 and 8 [[ohm]]s).

; [[Intermodulation distortion]] (IMD) 
: Distortion that is not harmonically related to the signal being amplified is intermodulation distortion. It is a measure of the level of spurious signals resulting from unwanted combination of different frequency input signals. This effect results from [[Nonlinear system|non-linearities in the system]]. Sufficiently high levels of negative feedback can reduce this effect in an amplifier.{{efn|Many{{who|date=April 2025}} believe it is better to design electronics in a way to minimize feedback levels, though this is difficult to achieve while meeting other high-accuracy requirements.}} Intermodulation in loudspeaker drivers is, as with harmonic distortion, almost always larger than in most electronics. IMD increases with cone excursion. Reducing a driver's bandwidth directly reduces IMD. This is achieved by splitting the desired frequency range into separate bands with an [[audio crossover]] and employing separate drivers for each band of frequencies.{{efn|Steep slope crossover filters are most effective at IMD reduction, but may be too expensive to implement using high-current components and may introduce ringing distortion.<ref>[http://www.xsgeo.com/course/filt.htm Excess Geophysics. ''FREQUENCY FILTERING in practice'']</ref>}} Intermodulation distortion in multi-driver loudspeaker systems can be greatly reduced with the use of [[active crossover]],{{cn|reason=What source of IMD is an active crossover eliminating?|date=April 2025}} though it significantly increases system cost and complexity.

; [[Noise (electronics)|Noise]] 
: The level of unwanted noise generated by the system itself, or by interference from external sources added to the signal. ''[[Hum (sound)|Hum]]'' usually refers to noise only at [[Utility frequency|power line frequencies]] (as opposed to e.g. broadband [[white noise]]), which is introduced through induction of power line signals into the inputs of gain stages, from inadequately regulated power supplies, or poor grounding of components. 

; [[Crosstalk]] 
: The introduction of noise (from another signal channel) caused by ground currents, stray inductance or capacitance between components or lines. Crosstalk reduces, sometimes noticeably, separation between channels (e.g., in a stereo system). A [[crosstalk measurement]] yields a figure in [[decibel]]s relative to a nominal level of signal in the path receiving interference. Crosstalk is normally only a problem in equipment that processes multiple audio channels in the same chassis.

; [[Common-mode rejection ratio]] (CMRR) 
: In [[balanced audio]] systems, there are equal and opposite signals in inputs, and any interference imposed on both leads will be subtracted, canceling out that interference. CMRR is a measure of a system's ability to ignore such interference and especially hum at its input. It is generally only significant with long lines on an input, or when some kinds of [[ground loop (electricity)|ground loop]] problems exist. Unbalanced inputs do not have common mode resistance; induced noise on their inputs appears directly as noise or hum.<!--[[User:Kvng/RTH]]-->

; [[Dynamic range]] ''and'' [[Signal-to-noise ratio]] (SNR) : The difference between the maximum level a component can accommodate and the noise level it produces. Input noise is not counted in this measurement. It is measured in dB.
: ''Dynamic range'' refers to the ratio of maximum to minimum loudness in a given signal source (e.g., music or programme material), and this measurement also quantifies the maximum dynamic range an audio system can carry. This is the ratio (usually expressed in [[decibel|dB]]) between the noise floor of the device with no signal and the maximum signal (usually a [[sine wave]]) that can be output at a specified (low) distortion level.
:Since the early 1990s it has been recommended by several authorities including the [[Audio Engineering Society]] that measurements of dynamic range be made with an audio signal present. This avoids questionable measurements based on the use of blank media or muting circuits.

: ''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&nbsp;dBu (IEC 60268-17), though sometimes 0&nbsp;dBu (UK and Europe – EBU standard Alignment level). 'Test level', 'measurement level' and 'line-up level' mean different things, often leading to confusion. In "consumer" equipment, no standard exists, though −10&nbsp;dBV and −6&nbsp;dBu are common.
: Different media characteristically exhibit different amounts of [[noise measurement|noise]] and [[Headroom (audio signal processing)|headroom]]. Though the values vary widely between units, a typical analogue [[Cassette tape|cassette]] might give 60&nbsp;dB, a [[CD]] almost 100&nbsp;dB. Most modern quality amplifiers have >110&nbsp;dB dynamic range,<ref>{{Cite web|url = http://www.zainea.com/Dynamic%20range.htm|title = Dynamic-Range Issues in the Modern Digital Audio Environment|last = FIELDER|first = LOUIS D.|date = 1 May 1995|website = zainea.com|publisher = Dolby Laboratories Inc., San Francisco, CA 91403, USA|access-date = 7 March 2016|archive-url = https://web.archive.org/web/20160626055428/http://www.zainea.com/Dynamic%20range.htm|archive-date = 26 June 2016|url-status = dead}}</ref> which approaches that of the human [[ear]], usually taken as around 130&nbsp;dB. See Programme levels.

; [[Phase distortion]]'', ''[[Group delay]]'', and ''[[Phase delay]] : A perfect audio component will maintain the [[phase (waves)|phase]] coherency of a signal over the full range of frequencies. Phase distortion can be extremely difficult to reduce or eliminate. The human ear is largely insensitive to phase distortion, though it is exquisitely sensitive to relative phase relationships within heard sounds. The complex nature of our sensitivity to phase errors, coupled with the lack of a convenient test that delivers an easily understood quality rating, is the reason that it is not a part of conventional audio specifications.{{Citation needed|date=October 2008}} Multi-driver loudspeaker systems may have complex phase distortions, caused or corrected by crossovers, driver placement, and the phase behaviour of the specific driver.

; [[Transient response]] : A system may have low distortion for a steady-state signal, but not on sudden transients. In amplifiers, this problem can be traced to power supplies in some instances, to insufficient high-frequency performance or to excessive negative feedback. Related measurements are [[slew rate]] and [[rise time]]. Distortion in transient response can be hard to measure. Many otherwise good power amplifier designs have been found to have inadequate slew rates, by modern standards. In loudspeakers, transient response performance is affected by the mass and resonances of drivers and enclosures and by [[group delay and phase delay]] introduced by crossover filtering or inadequate time alignment of the loudspeaker's drivers. Most [[loudspeaker]]s generate significant amounts of transient distortion, though some designs are less prone to this (e.g. [[electrostatic loudspeaker]]s, [[plasma arc loudspeaker|plasma arc tweeters]], [[ribbon tweeter]]s and [[Loudspeaker enclosure#Multiple entry horn|horn enclosures with multiple entry points]]).

; [[Damping factor]] : A higher number is generally believed to be better. This is a measure of how well a power [[amplifier]] controls the undesired motion of a [[loudspeaker]] driver. An amplifier must be able to suppress [[resonance]]s caused by mechanical motion (e.g., [[inertia]]) of a speaker cone, especially a low-frequency driver with greater mass. For conventional loudspeaker drivers, this essentially involves ensuring that the [[output impedance]] of the amplifier is close to zero and that the speaker wires are sufficiently short and have sufficiently large diameter. Damping factor is the ratio of the output impedance of an amplifier and connecting cables to the DC resistance of a [[voice coil]], which means that long, high resistance speaker wires will reduce the damping factor. A damping factor of 20 or greater is considered adequate for live [[sound reinforcement system]]s, as the SPL of inertia-related driver movement is 26&nbsp;dB less than signal level and won't be heard.<ref>[https://www.prosoundweb.com/what-is-loudspeaker-damping-damping-factor-df/ ProSoundWeb. Chuck McGregor, Community Professional Loudspeakers. January 2014. ''What is Loudspeaker Damping and Damping Factor (DF)?'']</ref> Negative feedback in an amplifier lowers its effective output impedance and thus increases its damping factor.<ref>[http://www.aikenamps.com/NegativeFeedback.htm Aiken Amplification. Randall Aiken. ''What is Negative Feedback?'' 1999] {{webarchive |url=https://web.archive.org/web/20081016103114/http://www.aikenamps.com/NegativeFeedback.htm |date=16 October 2008 }}</ref>