Broadband frequency translation for high frequency regeneration

Abstract

An audio signal is conveyed more efficiently by transmitting or recording a baseband of the signal with an estimated spectral envelope and a noise-blending parameter derived from a measure of the signal's noise-like quality. The signal is reconstructed by translating spectral components of the baseband signal to frequencies outside the baseband, adjusting phase of the regenerated components to maintain phase coherency, adjusting spectral shape according to the estimated spectral envelope, and adding noise according to the noise-blending parameter. Preferably, the transmitted or recorded signal also includes an estimated temporal envelope that is used to adjust the temporal shape of the reconstructed signal.

Description

[0001] The present invention relates generally to the transmission and recording of audio signals. More particularly, the present invention provides for a reduction of information required to transmit or store a given audio signal while maintaining a given level of perceived quality in the output signal.[0002] Many communications systems face the problem that the demand for information transmission and storage capacity often exceeds the available capacity. As a result there is considerable interest among those in the fields of broadcasting and recording to reduce the amount of information required to transmit or record an audio signal intended for human perception without degrading its subjective quality. Similarly there is a need to improve the quality of the output signal for a given bandwidth or storage capacity.[0003] Two principle considerations drive the design of systems intended for audio transmission and storage: the need to reduce information requirements and the need to e...

AI Technical Summary

Benefits of technology

0010] It is an object of the present invention to provide for the processing of audio signals to reduce the quantity of information required to represent a signal during transmission or storage while maintaining the perceived quality of the signal. Although the present invention is particularly directed toward the reproduction of music signals, it is also applicable to a wide range of audio signals including voice.

Problems solved by technology

Many communications systems face the problem that the demand for information transmission and storage capacity often exceeds the available capacity.

These two considerations conflict in that reducing the quantity of information transmitted can reduce the perceived quality of the output signal.

Although simple to implement, these HFR techniques are usually not suitable for high quality reproduction systems such as those used for high quality music.

Spectral folding and spectral translation can produce undesirable background tones.

Rectification tends to produce results that are perceived to be harsh.

The inventors have noted that in many cases where these techniques have produced unsatisfactory results, the techniques were used in bandlimited speech coders where HFR was restricted to the translation of components below 5 kHz.

The inventors have also noted two other problems that can arise from the use of HFR techniques.

The first problem is related to the tone and noise characteristics of signals, and the second problem is related to the temporal shape or envelope of regenerated signals.

Known HFR techniques regenerate high-frequency components from a baseband signal but fail to reproduce a proper mix of tone-like and noise-like components in the regenerated signal at the higher frequencies.

Furthermore, known HFR techniques fail to regenerate spectral components in such a way that the temporal envelope of the regenerated signal preserves or is at least similar to the temporal envelope of the original signal.

A number of more sophisticated HFR techniques have been developed that offer improved results; however, these techniques tend to be either speech specific, relying on characteristics of speech that are not suitable for music and other forms of audio, or require extensive computational resources that cannot be implemented economically.

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