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 perceived loudness of a digital audio signal, the method comprising:
deriving a plurality of scale factors for the digital audio signal to reduce a difference between the perceived loudness of the digital audio signal and a target loudness, each scale factor respectively operating in a frequency band of a plurality of frequency bands; and
applying the plurality of scale factors to the digital audio signal to reduce the difference between the perceived loudness and the target loudness;
wherein the perceived loudness varies both with frequency and acoustic level;
wherein the method is performed by one or more computing devices.
2. The method of claim 1 , further comprising time smoothing the plurality of scale factors.
3. The method of claim 1 , further comprising band smoothing of the plurality of scale factors.
4. The method of claim 1 , wherein the plurality of frequency bands are derived from a filter bank.
5. The method of claim 1 , wherein the digital audio signal is a discrete time sequence.
6. The method of claim 1 , wherein the applying the plurality of scale factors is configured to be selectable by a user.
7. An apparatus for controlling a perceived loudness of a digital audio signal, comprising:
a subsystem, implemented at least partially in hardware, that derives scale factors from the digital audio signal to reduce a difference between the perceived loudness and a target loudness, each scale factor respectively operating in a frequency band of a plurality of frequency bands;
a subsystem, implemented at least partially in hardware, that applies the scale factors to the digital audio signal to reduce the difference between the perceived loudness and the target loudness;
wherein the perceived loudness varies both with frequency and acoustic level.
8. The apparatus of claim 7 , further comprising a subsystem, implemented at least partially in hardware, that time smoothens the scale factors.
9. The apparatus of claim 7 , further comprising a subsystem, implemented at least partially in hardware, that band smoothens the scale factors.
10. The apparatus of claim 7 , wherein the plurality of frequency bands are derived from a filter bank.
11. The apparatus of claim 7 , wherein the digital audio signal is a discrete time sequence.
12. The apparatus of claim 7 , wherein the application of the scale factors is configured to be selectable by a user.
13. A non-transitory computer readable medium, storing software instructions for controlling a perceived loudness of a digital audio signal, which when executed by one or more processors cause performance of the steps of:
deriving a plurality of scale factors for the digital audio signal, each scale factor respectively operating in a frequency band of a plurality of frequency bands; and
applying the plurality of scale factors to the digital audio signal to reduce a difference between the perceived loudness of the digital audio signal and a target loudness;
wherein the perceived loudness varies both with frequency and acoustic level.
14. The non-transitory computer readable medium of claim 13 , further comprising time smoothing the scale factors.
15. The non-transitory computer readable medium of claim 13 , further comprising: band smoothing of the scale factors.
16. The non-transitory computer readable medium of claim 13 , wherein the plurality of frequency bands are derived from a filter bank.
17. The non-transitory computer readable medium of claim 13 , wherein the digital audio signal is a discrete time sequence.
18. The non-transitory computer readable medium of claim 13 , wherein applying the plurality of scale factors is configured to be selectable by a user.