Calculating and adjusting the perceived loudness and/or the perceived spectral balance of an audio signal
The invention relates to the measurement and control of the perceived sound loudness and/or the perceived spectral balance of an audio signal. An audio signal is modified in response to calculations performed at least in part in the perceptual (psychoacoustic) loudness domain. The invention is useful, for example, in one or more of: loudness-compensating volume control, automatic gain control, dynamic range control (including, for example, limiters, compressors, expanders, etc.), dynamic equalization, and compensating for background noise interference in an audio playback environment. The invention includes not only methods but also corresponding computer programs and apparatus.
1. A method for adjusting a level of an audio signal in an audio decoder, the method comprising:
dividing an audio signal into a plurality of frequency bands;
deriving modification parameters for at least some of the plurality of frequency bands, the modification parameters comprising amplitude scale factors, each amplitude scale factor respectively operating in a frequency band of a plurality of frequency bands and each amplitude scale factor representing an average energy over a frequency band and a time segment;
smoothing the modification parameters;
deriving gain factors for at least some of the plurality of frequency bands, the gain factors determined from the modification parameters and noise compensation factors, wherein the noise compensation factors are smoothed over time;
applying the gain factors to the at least some of the frequency bands; and
summing the plurality of frequency bands to generate a combined wideband audio signal,
wherein the gain factors are both time and frequency varying.
2. The method of claim 1 , further comprising band smoothing of the amplitude scale factors.
3. The method of claim 1 , wherein the plurality of frequency bands are derived from an analysis filter bank.
4. The method of claim 1 , wherein the summing is performed by a synthesis filterbank.
5. An audio decoder for adjusting a level of an audio signal, the audio decoder comprising:
an analysis filterbank for dividing an audio signal into a plurality of frequency bands;
a calculator for deriving modification parameters for at least some of the plurality of frequency bands, the modification parameters comprising amplitude scale factors, each amplitude scale factor respectively operating in a frequency band of a plurality of frequency bands and each amplitude scale factor representing an average energy over a frequency band and a time segment;
a smoother for smoothing the modification parameters;
a calculator for deriving gain factors for at least some of the plurality of frequency bands, the gain factors determined from the modification parameters and noise compensation factors, wherein the noise compensation factors are smoothed over time;
a processor for applying the gain factors to the at least some of the frequency bands; and
a synthesis filterbank for summing the plurality of frequency bands to generate a combined wideband audio signal,
wherein the gain factors are both time and frequency varying.
6. The audio decoder of claim 5 , further comprising a band smoother for smoothing the amplitude scale factors.
7. A non-transitory computer readable medium, storing software instructions for controlling a perceptual loudness of a digital audio signal, which when executed by one or more processors cause performance of the steps of:
dividing an audio signal into a plurality of frequency bands;
deriving modification parameters for at least some of the plurality of frequency bands, the modification parameters comprising amplitude scale factors, each amplitude scale factor respectively operating in a frequency band of a plurality of frequency bands and each amplitude scale factor representing an average energy over a frequency band and a time segment;
smoothing the modification parameters;
deriving gain factors for at least some of the plurality of frequency bands, the gain factors determined from the modification parameters and noise compensation factors, wherein the noise compensation factors are smoothed over time;
applying the gain factors to the at least some of the frequency bands; and
summing the plurality of frequency bands to generate a combined wideband audio signal,
wherein the gain factors are both time and frequency varying.
8. The non-transitory computer readable medium of claim 7 , further comprising band smoothing of the amplitude scale factors.
9. The non-transitory computer readable medium of claim 7 , wherein the plurality of frequency bands are derived from an analysis filter bank.
10. The non-transitory computer readable medium of claim 7 , wherein the summing is performed by a synthesis filterbank.