# US 10,636,448 B2 · Audio buffering for processing with variable lookahead > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 10,636,448 B2 - Document ID: US10636448B2 - Status: Granted - Kind: B2 - Application number: 16/133,433 - Filed: 2018-09-17 - Published: 2020-03-19 - Granted: 2020-04-28 - Earliest claimed: 2018-09-17 - Assignees: Apple Inc. - Applicants: Apple Inc. - Inventors: Frank Baumgarte - Web page: https://patentgrep.com/patent/US10636448B2 ## CPC - G11B 20/10046: {filtering or equalising, e.g. setting the tap weights of an FIR filter} - G06F 3/165: {Management of the audio stream, e.g. setting of volume, audio stream path} - G11B 20/10527: {Audio or video recording; Data buffering arrangements (G11B20/12 - G11B20/18 take precedence)} - G11B 27/038: Cross-faders therefor - H04R 3/04: for correcting frequency response - G11B 2020/10546: {specifically adapted for audio data} - G11B 2020/10666: {Ring buffers, e.g. buffers wherein an iteratively progressing read or write pointer moves back to the beginning of the buffer when reaching the last storage cell} - G11B 2020/10712: {buffer capacity, e.g. when the buffer capacity is exhausted, buffered data are overwritten with more recent data, accepting that the old data are lost} - H04R 2430/01: Aspects of volume control, not necessarily automatic, in sound systems - H04R 2430/03: Synergistic effects of band splitting and sub-band processing - G11B: INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER (recording measured values in a way that does not require playback through a transducer G01D9/00; recording or playback apparatus using mechanically marked tape, e.g. punched paper tape, or using unit records, e.g. punched or magnetically marked cards G06K; transferring data from one type of record carrier to another G06K1/18; circuits for coupling output of reproducer to radio receiver H04B1/20; gramophone pick-ups or like acoustic electromechanical transducers or circuits therefor H04R) - G06F: ELECTRIC DIGITAL DATA PROCESSING (computer systems based on specific computational models G06N) - H04R: LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS (producing sounds with frequency not determined by supply frequency G10K) ## Abstract An audio processing system has a buffer, a first digital signal processing module that uses a first lookahead, a second digital signal processing module that uses a second, greater lookahead, and a cross-fader. The cross-fader fades between the output of the first digital signal processing module to the output of the second digital signal processing module, based on lookahead depth of data of the audio signal in the buffer. Other aspects are also described and claimed. ## Claims ### Claim 1 An audio playback system, comprising: a buffer, to receive an audio signal; a first digital signal processing module to process the audio signal from the buffer using a first lookahead; a second digital signal processing module, to process the audio signal from the buffer using a second lookahead that is greater than the first lookahead; and a cross-fader to output a processed audio signal one at a time based on output of the first digital signal processing module or output of the second digital signal processing module, and fade the processed audio signal, from the output of the first digital signal processing module to the output of the second digital signal processing module or from the output of the second digital signal processing module to the output of the first digital signal processing module, based on data of the audio signal in the buffer. ### Claim 2 (depends on 1) The audio playback system of claim 1, further comprising: the cross-fader being configured to have hysteresis in the fade, to decrease frequency of cross-fading when depth of the data of the audio signal in the buffer drops below the second lookahead. ### Claim 3 (depends on 1) The audio playback system of claim 1, further comprising: the cross-fader being configured to fade the processed audio signal from the output of the first digital signal processing module to the output of the second digital signal processing module based on a determination that the depth of the data of the audio signal in the buffer exceeds a threshold amount. ### Claim 4 (depends on 1) The audio playback system of claim 1, further comprising: the cross-fader configured to fade the processed audio signal from the output of the second digital signal processing module to the output of the first digital signal processing module based on a determination of the depth of the data of the audio signal in the buffer is less than a threshold. ### Claim 5 (depends on 1) The audio playback system of claim 1, wherein the audio signal is a first sub-band signal, the system further comprising: an analysis filter bank or transform process configured to transform an input time domain audio signal into a plurality of sub-band signals one of which is the first sub-band signal; and a plurality of cross-faders to output a plurality of processed sub-band signals based on the plurality of sub-band signals, respectively. ### Claim 6 (depends on 1) The audio playback system of claim 1, further comprising: the first digital signal processing module configured to perform a first peak limiter process upon the audio signal from the buffer according to the first lookahead; and the second digital signal processing module configured to perform a second peak limiter process upon the audio signal from the buffer according to the second lookahead. ### Claim 7 (depends on 1) The audio playback system of claim 1, further comprising: the first digital signal processing module configured to have a first dynamic range compressor that processes the audio signal from the buffer according to the first lookahead; and the second digital signal processing module configured to have a second dynamic range compressor that processes the audio signal from the buffer according to the second lookahead. ### Claim 8 (depends on 1) The audio playback system of claim 1, further comprising: the first digital signal processing module configured to have a first loudness estimator that processes the audio signal from the buffer according to the first lookahead; and the second digital signal processing module configured to have a second loudness estimator that processes the audio signal from the buffer according to the second lookahead. ### Claim 9 (depends on 1) The audio playback system of claim 1, further comprising: the first digital signal processing module having a first loudness equalizer to process the audio signal from the buffer with frequency-based emphasis according to the first lookahead; and the second digital signal processing module having a second loudness equalizer to process the audio signal from the buffer with frequency-based emphasis according to the second lookahead. ### Claim 10 (depends on 1) The audio playback system of claim 1, further comprising: the first digital signal processing module having a first equalizer to spectrally balance the audio signal from the buffer according to the first lookahead; and the second digital signal processing module having a second equalizer to spectrally balance the audio signal from the buffer according to the second lookahead. ### Claim 11 A method of processing audio, performed by a processor, comprising: receiving an audio signal into a buffer; processing the audio signal from the buffer in a first digital signal processing module, using a first lookahead; processing the audio signal from the buffer in a second digital signal processing module, using a second, greater lookahead; and cross-fading a processed audio signal, between output of the first digital signal processing module and output of the second digital signal processing module, depending on lookahead depth of data of the audio signal in the buffer. ### Claim 12 (depends on 11) The method of processing audio of claim 11, further comprising: determining the lookahead depth of the data of the audio signal in the buffer is low relative to the first lookahead or the second lookahead, and in response using hysteresis in the cross-fading to decrease frequency of the cross-fading. ### Claim 13 (depends on 11) The method of processing audio of claim 11, wherein the cross-fading is from the output of the first digital signal processing module to the output of the second digital signal processing module based on the lookahead depth of the data of the audio signal in the buffer exceeding the second lookahead or a threshold. ### Claim 14 (depends on 11) The method of processing audio of claim 11, wherein the cross-fading is from the output of the second digital signal processing module to the output of the first digital signal processing module based on determining the lookahead depth of the data of the audio signal in the buffer is less than the second lookahead or a threshold. ### Claim 15 (depends on 11) The method of processing audio of claim 11, wherein: the processing the audio signal in first digital signal processing module comprises first automatic gain control according to the first lookahead; and the processing the audio signal in the second digital signal processing module comprises second automatic gain control according to the second lookahead. ### Claim 16 (depends on 11) The method of processing audio of claim 11, wherein: the processing the audio signal in the first digital signal processing module comprises first peak limiting according to the first lookahead; and the processing the audio signal in the second digital signal processing module comprises second peak limiting according to the second lookahead. ### Claim 17 An audio processing system comprising a processor and memory having stored therein instructions that when executed by the processor: process an audio signal from a buffer using a first lookahead to produce a first processed audio signal; process the audio signal from the buffer using a second, greater lookahead to produce a second processed audio signal; and cross-fade a processed audio signal, between the first processed audio signal and the second processed audio signal, depending on lookahead depth of data of the audio signal in the buffer. ### Claim 18 (depends on 17) The audio processing system of claim 17 where the lookahead depth is adjusted such that the first processed audio signal is synchronized in time with the second processed audio signal. ### Claim 19 (depends on 17) The audio processing system of claim 17 wherein the processor executes instructions stored in the memory to determine the lookahead depth of the data of the audio signal in the buffer is low relative to the first lookahead or the second lookahead, and in response uses hysteresis in the cross-fading to decrease frequency of the cross-fading. ### Claim 20 (depends on 17) The audio processing system of claim 17 wherein the cross-fading is from the first processed audio signal to the second processed audio signal, responsive to determining that the lookahead depth of the data of the audio signal in the buffer exceeds the second lookahead or a threshold. ### Claim 21 (depends on 17) The audio processing system of claim 17 wherein the cross-fading is from the second processed audio signal to the first processed audio signal, responsive to determining that the lookahead depth of the data of the audio signal in the buffer is less than the second lookahead or a threshold.