Abstract: Droop caused by a filter may be compensated by applying a pre-filter to the audio signal that cancels out, at least in part, the droop caused by the filter. The pre-filter may implement magnitude compensation that causes an approximately flat passband response when the pre-filtered signal is passed through the filter. The pre-filter may be applied to one-bit wide data streams, such as high-fidelity direct stream digital (DSD) audio data or other one-bit wide data such as pulse-density modulation (PDM) encoded data. The pre-filtering and filtering may be implemented in components of an audio processor, such as in a digital-to-analog converter (DAC). The pre-filtering may include upsampling the one-bit wide data to form symbols and substituting an eighth bit of the symbol with an inverted version of an earlier-received bit.

Abstract: An audio processor may process dissimilarly formatted digital audio signals and produce an analog output for reproduction by a transducer, such as a speaker. The audio processor may be, for example, a digital-to-analog converter (DAC) with multiple digital inputs and a single analog output. The audio processor may also include other components, such as processing components, filters, equalizers, amplifiers, and the like. The audio processor may process audio, such as high fidelity DSD audio and lower fidelity PCM audio, and combine the differently formatted data into a single output. During processing, the audio processor may manipulate the different audio signals, such as by ducking a music playback to allow a notification sound to be played.

Abstract: The behavior of a NOS DAC and an analog filter may be emulated by electronic components of an integrated circuit (IC) by upsampling data and applying a digital filter to the upsampled data. For example, the IC may include a zero-order-hold circuit that upsamples data from a first input sample rate to a second, higher input rate. The upsampled data may be passed to an Asynchronous Sample Rate Converter (ASRC) that performs further upsampling (e.g., from 8*Fs-64*Fs). The upsampled data may be passed to a digital low pass filter. The digital low pass filter may emulate, for example, a response of a fifth order Butterworth analog filter to mimic the effect of analog processing. The IC may integrate the upsampling circuit, the low pass digital filter, a digital-to-analog converter (DAC) and an amplifier to provide an audio solution for playing high-fidelity music in a mobile device.

Abstract: A digital volume control may be implemented in a digital-to-analog controller (DAC) when an output rate of the DAC is higher than the input rate. The upsampling conversion process from the digital input to analog output may be controlled to adjust a volume of an output signal produced from the digital signals. The frames produced by the upsampling conversion process may include a fraction of scheduling blocks filled with the input data bit, where the fraction is based on a desired volume. The generated frames are provided to a finite impulse response (FIR) filter that produces an analog signal with a magnitude proportional to the determined fraction of scheduling blocks.

Abstract: A digital volume control may be implemented in a digital-to-analog controller (DAC) when an output rate of the DAC is higher than the input rate. The upsampling conversion process from the digital input to analog output may be controlled to adjust a volume of an output signal produced from the digital signals. The frames produced by the upsampling conversion process may include a fraction of scheduling blocks filled with the input data bit, where the fraction is based on a desired volume. The generated frames are provided to a finite impulse response (FIR) filter that produces an analog signal with a magnitude proportional to the determined fraction of scheduling blocks.

Abstract: Droop caused by a filter may be compensated by applying a pre-filter to the audio signal that cancels out, at least in part, the droop caused by the filter. The pre-filter may implement magnitude compensation that causes an approximately flat passband response when the pre-filtered signal is passed through the filter. The pre-filter may be applied to one-bit wide data streams, such as high-fidelity direct stream digital (DSD) audio data or other one-bit wide data such as pulse-density modulation (PDM) encoded data. The pre-filtering and filtering may be implemented in components of an audio processor, such as in a digital-to-analog converter (DAC). The pre-filtering may include upsampling the one-bit wide data to form symbols and substituting an eighth bit of the symbol with an inverted version of an earlier-received bit.

Abstract: An audio processor may process dissimilarly formatted digital audio signals and produce an analog output for reproduction by a transducer, such as a speaker. The audio processor may be, for example, a digital-to-analog converter (DAC) with multiple digital inputs and a single analog output. The audio processor may also include other components, such as processing components, filters, equalizers, amplifiers, and the like. The audio processor may process audio, such as high fidelity DSD audio and lower fidelity PCM audio, and combine the differently formatted data into a single output. During processing, the audio processor may manipulate the different audio signals, such as by ducking a music playback to allow a notification sound to be played.

Abstract: The behavior of a NOS DAC and an analog filter may be emulated by electronic components of an integrated circuit (IC) by upsampling data and applying a digital filter to the upsampled data. For example, the IC may include a zero-order-hold circuit that upsamples data from a first input sample rate to a second, higher input rate. The upsampled data may be passed to an Asynchronous Sample Rate Converter (ASRC) that performs further upsampling (e.g., from 8*Fs-64*Fs). The upsampled data may be passed to a digital low pass filter. The digital low pass filter may emulate, for example, a response of a fifth order Butterworth analog filter to mimic the effect of analog processing. The IC may integrate the upsampling circuit, the low pass digital filter, a digital-to-analog converter (DAC) and an amplifier to provide an audio solution for playing high-fidelity music in a mobile device.

Abstract: A DC servo loop may track DC offset changes of an input signal and apply feedback to amplifiers to adjust a DC offset of the input signal. The DC servo loop may include digital loop tracking and analog loop tracking components. The digital loop tracking components may track small changes in the DC offset. When the DC offset exceeds a certain threshold, analog loop tracking may be activated to apply feedback to the amplifiers to adjust the DC offset. The adjustments to the DC offset may be delayed until an amplitude of the input signal exceeds a threshold to reduce contribution to noise in the input signal.

Abstract: Methods and Apparatuses are provided for automatically converting a word length of sample data being transmitted over a serial link. A serial interface transmits and/or receives one or more data words comprising digital signals, a bit clock synchronizes transmission of individual bits, and a word clock is used to group the bits into sample words. A desired word length is determined based on the relationship between the bit clock and the word clock during the transmission or reception of a data word. Based on the desired word length, the sample data is either truncated or padded, and an appropriate amount of dither is added to the sample words to reduce the distortion and quantization artifacts introduced by the word length conversion.

Abstract: A method of performing sample rate conversion in a data converter operating from an oversampling clock corresponding to a native sample rate and a native oversampling factor. A virtual sample rate and a virtual oversampling factor are selected proportional to the native sample rate and the native oversampling factor. A data stream having a data sample rate is sampled by the virtual oversampling factor. The data stream is also resampled with a resampling ratio approximating a ratio of the data sample rate to the virtual sample rate.