Loading patent…
AssigneeCoding Technologies Sweden AB
InventorsLars Liljeryd, Per Ekstrand, Fredrik Henn, Kristofer Kjoerling
Estimating the term…
The present invention relates to a new method and apparatus for improvement of High Frequency Reconstruction (HFR) techniques using frequency translation or folding or a combination thereof. The proposed invention is applicable to audio source coding systems, and offers significantly reduced computational complexity. This is accomplished by means of frequency translation or folding in the subband domain, preferably integrated with spectral envelope adjustment in the same domain. The concept of dissonance guard-band filtering is further presented. The proposed invention offers a low-complexity, intermediate quality HFR method useful in speech and natural audio coding applications.
Method for obtaining an envelope adjusted and frequency-translated signal by high-frequency spectral reconstruction of complex subband signals in channels within a reconstruction range using complex subband signals in source area channels derived from a lowband signal, using a digital filter bank having an analysis part and a synthesis part, the method comprising:
Method for obtaining an envelope adjusted and frequency-folded signal by high-frequency spectral reconstruction of complex subband signals in channels within a reconstruction range using complex subband signals in source area channels derived from a lowband signal, using a digital filter bank having an analysis part and a synthesis part, the method comprising:
Apparatus for obtaining an envelope adjusted and frequency-translated signal by high-frequency spectral reconstruction of complex subband signals in channels within a reconstruction range using complex subband signals in source area channels derived from a lowband signal, comprising:
Apparatus for obtaining an envelope adjusted and frequency-folded signal by high-frequency spectral reconstruction of complex subband signals in channels within a reconstruction range using complex subband signals in source area channels derived from a lowband signal, comprising:
Decoder for decoding coded signals, the coded signals comprising a coded lowband audio signal, comprising:
Decoder for decoding coded signals, the coded signals comprising a coded lowband audio signal, comprising:
Method for decoding coded signals, the coded signals comprising a coded lowband audio signal, the method comprising:
Method for decoding coded signals, the coded signals comprising a coded lowband audio signal, the method comprising:
Dependencies are inferred from the claim text.
Drawings are temporarily unavailable. Open the PDF at USPTO
From the US filing history. Foreign family members aren’t listed.
Using subband decomposition: subband vocoders
Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals,…:…
Using predictive techniques: pre-filtering or post-filtering
Pre-filtering or post-filtering: pre-filtering, e.g. high frequency emphasis prior to encoding
Term ended 6 Jan 2024 (estimated)
The present invention relates to a new method and apparatus for improvement of High Frequency Reconstruction (HFR) techniques, applicable to audio source coding systems. Significantly reduced computational complexity is achieved using the new method. This is accomplished by means of frequency translation or folding in the subband domain, preferably integrated with the spectral envelope adjustment process. The invention also improves the perceptual audio quality through the concept of dissonance guard-band filtering. The proposed invention offers a low-complexity, intermediate quality HFR method and relates to the PCT patent Spectral Band Replication (SBR) [WO 98/57436].
Schemes where the original audio information above a certain frequency is replaced by gaussian noise or manipulated lowband information are collectively referred to as High Frequency Reconstruction (HFR) methods. Prior-art HFR methods are, apart from noise insertion or non-linearities such as rectification, generally utilizing so-called copy-up techniques for generation of the highband signal. These techniques mainly employ broadband linear frequency shifts, i.e. translations, or frequency inverted linear shifts, i.e. foldings. The prior-art HFR methods have primarily been intended for the improvement of speech codec performance. Recent developments in highband regeneration using perceptually accurate methods, have however made HFR methods successfully applicable also to natural audio codecs, coding music or other complex programme material, PCT patent [WO 98/57436]. Under certain conditions, simple copy-up techniques have shown to be adequate when coding complex programme material as well. These techniques have shown to produce reasonable results for intermediate quality applications and in particular for codec implementations where there are severe constraints for the computational complexity of the overall system.
The human voice and most musical instruments generate quasistationary tonal signals that emerge from oscillating systems. According to Fourier theory, any periodic signal may be expressed as a sum of sinusoids with frequencies f, 2f, 3f, 4f, 5f etc. where f is the fundamental frequency. The frequencies form a harmonic series. Tonal affinity refers to the relations between the perceived tones or harmonics. In natural sound reproduction such tonal affinity is controlled and given by the different type of voice or instrument used. The general idea with HFR techniques is to replace the original high frequency information with information created from the available lowband and subsequently apply spectral envelope adjustment to this information. Prior-art HFR methods create highband signals where tonal affinity often is uncontrolled and impaired. The methods generate non-harmonic frequency components which cause perceptual artifacts when applied to complex programme material. Such artifacts are referred to in the coding literature as “rough” sounding and are perceived by the listener as distortion.
The present invention is described by way of illustrative examples, not limiting the scope or spirit of the invention, with reference to the accompanying drawings, in which:
FIG. 1 illustrates filterbank-based translation or folding integrated in a coding system according to the present invention;
FIG. 2 shows a basic structure of a maximally decimated filterbank;
Digital Filterbank Based Translation and Folding
New filter bank based translating or folding techniques will now be described. The signal under consideration is decomposed into a series of subband signals by the analysis part of the filterbank. The subband signals are then repatched, through reconnection of analysis-and synthesis subband channels, to achieve spectral translation or folding or a combination thereof.
FIG. 2 shows the basic structure of a maximally decimated filterbank analysis/synthesis system. The analysis filter bank 201 splits the input signal into several subband signals. The synthesis filter bank 202 combines the subband samples in order to recreate the original signal. Implementations using maximally decimated filter banks will drastically reduce computational costs. It should be appreciated, that the invention can be implemented using several types of filter banks or transforms, including cosine or complex exponential modulated filter banks, filter bank interpretations of the wavelet transform, other non-equal bandwidth filter banks or transforms and multi-dimensional filter banks or transforms.