Circuit and apparatus having a delay unit for reducing periodic noise

An audio signal processing circuit comprising:

• a first filter including,
• a counter arranged to receive periodicity information synchronized with periodicity of a periodic noise included in an input audio signal and to convert the periodicity information to delay information,
• a variable delaying unit configured to receive the delay information from the counter and to carry out delay processing so as to delay a level adjusted signal supplied thereto by an amount of time determined on the basis of the delay information, and
• a filter unit configured to receive the input audio signal, the filter unit having a notch characteristic at a frequency f, the frequency f satisfying f=N/T, where N represents an integer equal to or greater than one and T represents a delaying time applied by the delaying unit,
• in which the level adjusted signal is supplied to the variable delaying unit from the filter unit;
• a second filter, including
• an adaptive filter unit configured to output a pseudo noise signal approximating the periodic noise on the basis of the periodicity information, and
• a subtraction unit configured to subtract the pseudo noise signal from the input audio signal;
• and
• a switching unit configured to switch between outputting a first output of the first filter and a second output of the second filter and to output either the first output or the second output, the switching unit outputting the first output from the first filter at a time when the periodicity of the periodic noise changes and during a predetermined time after the time when the periodicity of the periodic noise changes.

An imaging apparatus comprising:

• an imaging unit configured to capture light from an object and to output an image signal;
• an audio pick-up unit configured to pick up sound and output an audio signal;
• an audio signal processing unit configured to carry out signal processing on the audio signal output from the audio pick-up unit;
• and
• a recording unit having a rotary mechanism, the recording unit being capable of recording an image signal output from the imaging unit and an audio signal output from the audio signal processing unit onto a recording medium,
• wherein the audio signal processing unit includes,
• a first filter having,
• a counter arranged to receive periodicity information synchronized with periodicity of a periodic noise included in the audio signal output form the audio pick-up unit and to convert the periodicity information to delay information,
• a variable delaying unit configured to receive the delay information from the counter and to carry out delay processing so as to delay a level adjusted signal supplied thereto by an amount of time determined on the basis of the delay information, and
• a filter unit configured to receive the audio signal output form the audio pick-up unit, the filter unit having a notch characteristic at a frequency f, the frequency f satisfying f=N/T, where N represents an integer equal to or greater than one and T represents a delaying time applied by the delaying unit,
• in which the level adjusted signal is supplied to the variable delaying unit from the filter unit;
• a second filter having,
• an adaptive filter unit configured to output a pseudo noise signal approximating the periodic noise on the basis of the periodicity information, and
• a subtraction unit configured to subtract the pseudo noise signal from the audio signal output form the audio pick-up unit, and
• a switching unit configured to switch between outputting a first output from the first filter and a second output from the second filter and to output either the first output or the second output, the switching unit outputting the first output from the first filter at a time when the periodicity of the periodic noise changes and during a predetermined time after the time when the periodicity of the periodic noise changes.

A recording apparatus comprising:

• an audio pick-up unit configured to pick up sound and output an audio signal;
• an audio signal processing unit configured to carry out signal processing on the audio signal output from the audio pick-up unit;
• and
• a recording unit having a rotary mechanism, the recording unit being capable of recording an audio signal output from the audio signal processing unit,
• wherein the audio signal processing unit includes,
• a first filter having,
• a counter arranged to receive periodicity information synchronized with periodicity of a periodic noise included in the audio signal output from the audio pick-up unit and to convert the periodicity information to delay information,
• a variable delaying unit configured to receive the delay information from the counter and to carry out delay processing so as to delay a level adjusted signal supplied thereto by an amount of time determined on the basis of the delay information, and
• a filter unit configured to receive the audio signal output from the audio pick-up unit, the filter unit having a notch characteristic at a frequency f, the frequency f satisfying f=N/T, where N represents an integer equal to or greater than one and T represents a delaying time applied by the delaying unit,
• in which the level adjusted signal is supplied to the variable delaying unit from the filter unit, and
• a second filter having,
• an adaptive filter unit configured to output a pseudo noise signal approximating the periodic noise on the basis of the periodicity information, and
• a subtraction unit configured to subtract the pseudo noise signal from the audio signal output from the audio pick-up unit, and
• a switching unit configured to switch between outputting a first output from the first filter and a second output from the second filter and to output either the first output or the second output, the switching unit outputting the first output from the first filter at a time when the periodicity of the periodic noise changes and during a predetermined time after the time when the periodicity of the periodic noise changes.

A playing apparatus comprising:

• a playing unit configured to play an audio signal, the playing unit including a rotary mechanism;
• an audio signal processing unit configured to carry out signal processing on the audio signal output from the playing unit;
• and
• an audio output unit configured to output an audio signal output from the signal processing unit,
• wherein the audio signal processing unit includes,
• a first filter having,
• a counter arranged to receive periodicity information synchronized with periodicity of a periodic noise included in the audio signal output from the playing unit and to convert the periodicity information to delay information,
• a variable delaying unit configured to receive the delay information from the counter and to carry out delay processing so as to delay a level adjusted signal supplied thereto by an amount of time determined on the basis of the delay information, and
• a filter unit configured to receive the audio signal output from the audio playing unit, the filter unit having a notch characteristic at a frequency f, the frequency f satisfying f=N/T, where N represents an integer equal to or greater than one and T represents a delaying time applied by the delaying unit,
• in which the level adjusted signal is supplied to the variable delaying unit from the filter unit, and
• a second filter having,
• an adaptive filter unit configured to output a pseudo noise signal approximating the periodic noise on the basis of the periodicity information, and
• a subtraction unit configured to subtract the pseudo noise signal from the audio signal output from the audio playing unit;
• and
• a switching unit configured to switch between outputting a first output from the first filter and a second output from the second filter and to output either the first output or the second output, the switching unit outputting the first output from the first filter at a time when the periodicity of the periodic noise changes and during a predetermined time after the time when the periodicity of the periodic noise changes.