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The noise current is set by the filament temperature. The current is an exponential function of filament temperature. At low frequencies, there is 1/f noise. At high frequencies, the transit time of the electron becomes an issue. Ott (1976, pp. 218–219) describes using a noise diode to measure noise factor.
The measure of the low frequency (many tens of Hz) noise contributed by the turntable of an analogue playback system. It is caused by imperfect bearings, uneven motor windings, vibrations in driving bands in some turntables, room vibrations (e.g., from traffic) that is transmitted by the turntable mounting and so to the phono cartridge.
Audio noise measurement is a process carried out to assess the quality of audio equipment, such as the kind used in recording studios, broadcast engineering, and in-home high fidelity. In audio equipment noise is a low-level hiss or buzz that intrudes on audio output.
The noise figure is the difference in decibel (dB) between the noise output of the actual receiver to the noise output of an "ideal" receiver with the same overall gain and bandwidth when the receivers are connected to matched sources at the standard noise temperature T 0 (usually 290 K). The noise power from a simple load is equal to kTB ...
ITU-R 468 (originally defined in CCIR recommendation 468-4, therefore formerly also known as CCIR weighting; sometimes referred to as CCIR-1k) is a standard relating to noise measurement, widely used when measuring noise in audio systems.
A measurement system analysis (MSA) is a thorough assessment of a measurement process, and typically includes a specially designed experiment that seeks to identify the components of variation in that measurement process. Just as processes that produce a product may vary, the process of obtaining measurements and data may also have variation ...
A recording is made with the low frequencies reduced and the high frequencies boosted, and on playback, the opposite occurs. The net result is a flat frequency response, but with attenuation of high-frequency noise such as hiss and clicks that arise from the recording medium. Reducing the low frequencies also limits the excursions the cutter ...
The measuring microphone is normally mounted on an unobtrusive boom (to avoid reflections) and positioned 1 metre in front of the drive units on the axis with the high-frequency driver. While this can produce repeatable results, such a 'free-space' measurement is not representative of performance in a room, especially a small room.