A noise cancellation system, comprising: an input for a digital signal, the digital signal having a first sample rate; a digital filter, connected to the input to receive the digital signal; a decimator, connected to the input to receive the digital signal and to generate a decimated signal at a second sample rate lower than the first sample rate; and a processor. The processor comprises: an emulation of the digital filter, connected to receive the decimated signal and to generate an emulated filter output; and a control circuit, for generating a control signal on the basis of the emulated filter output. The control signal is applied to the digital filter to control a filter characteristic thereof.

This disclosure describes circuit configurations that may be used for active noise cancellation in the digital domain. In particular, this disclosure proposes the use a down sample unit and an up sample unit, rather than memory-based delay circuits, to achieve one or more desired delays in digital adaptive noise cancellation circuits or other circuits that use delay for signal processing. The delay achieved by the down sample unit and the up sample unit may be tunable so as to allow flexibility in producing the necessary delay for different active noise cancellation circuit configurations. Many different adaptive noise cancellation circuit configurations are discussed, and the techniques may also be useful for other types of circuits, such as low-latency equalization circuits.

Various aspects include active noise reduction (ANR) headsets and methods of controlling such headsets. In some implementations, a headset includes: at least one electro-acoustic transducer; a power source for powering the at least one electro-acoustic transducer; and a control circuit configured to apply active noise reduction (ANR) to environmental sound using the at least one electro-acoustic transducer, sample voltage drops across the power source, and adjust a compressor threshold for the ANR based on the sampled voltage drops across the power source.

A noise cancellation system, comprising: an input for a digital signal, the digital signal having a first sample rate; a digital filter, connected to the input to receive the digital signal; a decimator, connected to the input to receive the digital signal and to generate a decimated signal at a second sample rate lower than the first sample rate; and a processor. The processor comprises: an emulation of the digital filter, connected to receive the decimated signal and to generate an emulated filter output; and a control circuit, for generating a control signal on the basis of the emulated filter output. The control signal is applied to the digital filter to control a filter characteristic thereof.

A method and system to monitor and adjust sound waves. The system includes microphone unit, noise-cancellation circuitry, input audio source, processing unit, and microcontroller unit. The microphone unit detects ambient sound waves after turning on microphone unit. The noise-cancellation circuitry creates sound waves that are 180 degrees out of phase with the detected ambient sound waves to cancel ambient sound waves. The processing unit processes sound waves received from noise-cancellation circuitry and audio signals received from input audio source into output sound waves, and further measures quantified level of loudness of output sound waves. The microcontroller unit aggregates, and compares received quantified level of loudness of output sound waves with a pre-stored quantified value of sound waves. The processing unit adjusts output sound waves to pre-defined value of sound waves in case compared quantified level of loudness of output sound waves exceeds from the pre-stored quantified value of sound waves.

An audio system can include an analog portion having multiple input sensors and an output device, a first digital portion running at a first rate and having a first processor that is electrically coupled with the input sensors and the output device, and a second digital portion running at a second rate that is higher than the first rate and having a second processor that is electrically coupled with the first processor.

A vehicle includes a music signal processing system having a loudspeaker disposed within a passenger compartment of the vehicle and emitting audible music into the passenger compartment. A microphone is disposed within the passenger compartment and converts the audible music and noise within the passenger compartment into an analog electrical microphone signal. An analog-to-digital converter is connected to an output of the microphone and receives the analog electrical microphone signal and converts the analog electrical microphone signal into a digital electrical microphone signal. A sample rate down converter is connected to an output of the analog-to-digital converter. A narrow band adaptive noise control is connected to an output of the sample rate down converter and receives an engine speed signal. A sample rate up converter is connected to an output of the narrow band adaptive noise control. An adder device adds an output of the sample rate up converter to a music signal. A digital-to-analog converter is connected to an output of the adder device. An amplifier has an input connected to an output of the digital-to-analog converter. An output of the amplifier is connected to an input of the loudspeaker.

A maximum noise suppression level (G.sub.min) is not a single constant value for an entire frequency range, but is allowed to vary across frequencies. The amount of variation is dynamically computed based on the input noise characteristics. For example, if there is excess noise in the lower frequency region, the maximum noise suppression level in that region will increase to suppress the noise in that frequency region. This feature can be enabled all the time, and will be active when the input conditions warrant extra noise suppression in a particular frequency region. Thus, the effort involved in manually tuning an audio system (e.g., hands-free telephony, voice-controlled automotive head unit, etc.) can be significantly reduced or eliminated.

An audio system having low latency includes a digital audio processor as well as sensor inputs coupled to the processor. The sensor inputs may be microphone inputs. The audio processor operates at the same frequency as the sensor inputs, which is typically much higher than an audio signal provided to the audio processor. In some aspects the audio processor operates as a noise cancellation processor and does not include an audio input.

An earphone noise reduction method and apparatus, which are applicable to the technical field of wearable devices. The earphone noise reduction method can include collecting, using an earphone microphone, a noise signal of an environment where the earphone microphone is placed. The method can also include transmitting the noise signal to a connected terminal or transmitting a noise value corresponding to the noise signal to the connected terminal. The method can further include receiving a judgement result returned by the terminal, and enabling a noise reduction function or disabling the noise reduction function according to the judgement result. Embodiments of the present disclosure can be realized without keys or toggle switches for noise reduction adjustment on earphones. Embodiments of the present disclosure are capable of automatic noise reduction, thereby improving the integration degree of the earphones and also enhancing the battery life of the earphones.