μ-law

μ-law

Das µ-law-Verfahren (oft u-law geschrieben) ist ein Digitalisierungsverfahren für analoge Audiosignale, das in der Empfehlung G.711 der International Telecommunication Union (ITU) standardisiert ist. In ähnlicher Weise wie das A-law-Verfahren arbeitet das µ-law-Verfahren mit einer logarithmischen Quantisierungskennlinie, um ein besseres Signal-Rausch-Verhältnis zu erzielen.

Kennlinien von A-law und µ-law und lineare Quantisierung im Vergleich

Ebenso wie bei diesem Verfahren werden jeweils 8-Bit-Werte erzeugt. Jedoch ist die Quantisierungskennlinie bei niedrigen Pegeln steiler. Außerdem ist die Codierung darauf ausgelegt, keine kontinuierlichen 0-Folgen zu erzeugen, sondern ständig wechselnde Bitzustände. Damit wird ein bestimmtes Verfahren zur Taktrückgewinnung beim Empfänger des digitalen Signals erleichtert. Das µ-law-Verfahren wird von der PCM-Technik in Nordamerika und Japan verwendet.

f_\mu(x) = \sgn(x) \frac{\ln(1+\mu\cdot|x|)}{\ln(1+\mu)} mit μ = 255, wobei sgn(x) das Vorzeichen von x ist.

Die Quantisierungskennlinie ist bei diesem Verfahren in 15 Segmente unterteilt.

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