Addition of virtual bass in the frequency domain

An apparatus for processing an audio signal, comprising:

• (a) an input line that inputs an original audio signal;
• (b) a transform module that transforms the original audio signal into a set of frequency components;
• (c) a bass extraction filter that extracts a bass portion of said frequency components;
• (d) an estimator that estimates a fundamental frequency of a bass sound within said bass portion;
• (e) a frequency translator that shifts the bass portion by a positive frequency increment that is an integer multiple of the fundamental frequency estimated by said estimator, thereby providing a virtual bass signal;
• (f) an adder having (i) inputs coupled to said original audio signal and to said virtual bass signal and (ii) an output;
• (g) an audio output device coupled to the output of said adder;
• and
• (h) a loudness controller that adjusts a strength of said virtual bass signal based on a first estimate of a perceived loudness of said bass portion and a second estimate of a perceived loudness of said virtual bass signal,
• wherein the loudness controller determines a scale factor based on a representative frequency for the bass portion, a strength of the bass portion, a representative frequency for the virtual bass signal and an equal-loudness-level data set.

An apparatus for processing an audio signal, comprising:

• (a) an input line that inputs an original audio signal;
• (b) a transform module that transforms the original audio signal into a set of frequency components;
• (c) a bass extraction filter that extracts a bass portion of said frequency components;
• (d) an estimator that estimates a fundamental frequency of a bass sound within said bass portion;
• (e) a frequency translator that shifts the bass portion by a positive frequency increment that is an integer multiple of the fundamental frequency estimated by said estimator, thereby providing a virtual bass signal;
• (f) an adder having (i) inputs coupled to said original audio signal and to said virtual bass signal and (ii) an output;
• and
• (g) an audio output device coupled to the output of said adder,
• wherein said estimator also estimates a salience value of said bass sound, and wherein said virtual bass signal is forced to 0 if said salience value does not satisfy a specified criterion.

An apparatus for processing an audio signal, comprising:

• (a) an input line that inputs an original audio signal;
• (b) a transform module that transforms the original audio signal into a set of frequency components;
• (c) a bass extraction filter that extracts a bass portion of said frequency components;
• (d) an estimator that estimates a fundamental frequency of a bass sound within said bass portion;
• (e) a frequency translator that shifts the bass portion by a positive frequency increment that is an integer multiple of the fundamental frequency estimated by said estimator, thereby providing a virtual bass signal;
• (f) an adder having (i) inputs coupled to said original audio signal and to said virtual bass signal and (ii) an output;
• and
• (g) an audio output device coupled to the output of said adder,
• wherein the integer multiple is determined as
• k
• =
• ⌈
• f
• l
• t
• f
• l
• b
• ⌉
• -
• 1
• ,
• where k is the integer multiple, flb is a low- and cut off frequency of a bandpass filter that functions as the bass extraction filter, flt denotes a designated lowest acceptable frequency, and ┌x┐ is a ceiling function which returns a smallest integer that is not less than x.

An apparatus for processing an audio signal, comprising:

• (a) an input line that inputs an original audio signal;
• (b) a transform module that transforms the original audio signal into a set of frequency components;
• (c) a bass extraction filter that extracts a bass portion of said frequency components;
• (d) an estimator that estimates a fundamental frequency of a bass sound within said bass portion;
• (e) a frequency translator that shifts the bass portion by a positive frequency increment that is an integer multiple of the fundamental frequency estimated by said estimator, thereby providing a virtual bass signal;
• (f) an adder having (i) inputs coupled to said original audio signal and to said virtual bass signal and (ii) an output;
• and
• (g) an audio output device coupled to the output of said adder,
• wherein the integer multiple is determined as
• k
• =
• ⌈
• f
• l
• t
• F
• 0
• ⌉
• -
• 1
• ,
• where k is the integer multiple, F0 is the fundamental frequency, flt denotes a designated lowest acceptable frequency, and ┌x┐ is a ceiling function which returns a smallest integer that is not less than x.

An apparatus for processing an audio signal, comprising:

• (a) an input line that inputs an original audio signal;
• (b) a transform module that transforms the original audio signal into a set of frequency components;
• (c) a bass extraction filter that extracts a bass portion of said frequency components;
• (d) an estimator that estimates a fundamental frequency of a bass sound within said bass portion;
• (e) a frequency translator that shifts the bass portion by a positive frequency increment that is an integer multiple of the fundamental frequency estimated by said estimator, thereby providing a virtual bass signal;
• (f) an adder having (i) inputs coupled to said original audio signal and to said virtual bass signal and (ii) an output;
• and
• (g) an audio output device coupled to the output of said adder,
• wherein the integer multiple is determined as
• k
• =
• ⌈
• f
• l
• t
• +
• 1
• 2
• ⁢
• f
• h
• b
• -
• f
• l
• b
• 1
• 2
• ⁢
• f
• h
• b
• ⌉
• -
• 1
• ,
• where k is the integer multiple, flt denotes a designated lowest acceptable frequency, flb is a low-end cutoff frequency of a bandpass filter that functions as the bass extraction filter, fhb is a high-end cutoff frequency of the bass extraction filter, and ┌x┐ is a ceiling function which returns a smallest integer that is not less than x.