# US 5,710,387 A · Method for recognition of the start of a note in the case of percussion or plucked musical instruments > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,710,387 A - Document ID: US5710387A - Status: Granted - Kind: A - Application number: 08/585,165 - Filed: 1996-01-11 - Granted: 1998-01-20 - Earliest claimed: 1995-01-12 - Assignees: Yamaha Corporation - Inventors: Andreas Szalay - Web page: https://patentgrep.com/patent/US5710387A ## CPC - G10H 3/125: {Extracting or recognising the pitch or fundamental frequency of the picked up signal} - G10H 1/057: by envelope-forming circuits - G10H 3/12: using mechanical resonant generators, e.g. strings or percussive instruments, the tones of which are picked up by electromechanical transducers, the electrical signals being further manipulated or amplified and subsequently converted to sound by a loudspeaker or equivalent instrument - G10H 3/146: {using a membrane, e.g. a drum; Pick-up means for vibrating surfaces, e.g. housing of an instrument} - G10H: ELECTROPHONIC MUSICAL INSTRUMENTS; INSTRUMENTS IN WHICH THE TONES ARE GENERATED BY ELECTROMECHANICAL MEANS OR ELECTRONIC GENERATORS, OR IN WHICH THE TONES ARE SYNTHESISED FROM A DATA STORE ## Abstract A method is specified for recognition of the start of a note in the case of percussion or plucked musical instruments, in the case of which an envelope curve following function is formed from an audio signal, a comparison variable is formed from a current value of the envelope curve following function and a predecessor value corresponding to an earlier value, and the start of a note is defined at a point in time at which the comparison value exceeds a threshold value. ## Claims ### Claim 1 A method for recognition of the start of a note in the case of percussion or plucked musical instruments, comprising the steps of: providing an audio signal from the musical instrument; forming an envelope curve following function from the audio signal, forming a comparison value from a current value of the envelope curve following function and a predecessor value corresponding to an earlier value of the envelope curve following function, and providing a start of a note signal at a point in time at which the comparison value exceeds a threshold value. ### Claim 2 (depends on 1) The method as claimed in claim 1, wherein a check is carried out to determine whether the envelope curve following function rises still further, in particular before the threshold value comparison. ### Claim 3 (depends on 1) The method as claimed in claim 1, wherein the comparison value is determined in constant time sections. ### Claim 4 (depends on 1) The method as claimed in claim 1, wherein a minimum value function is formed from the envelope curve following function, and the comparison value is formed from the envelope curve following function and the minimum value function. ### Claim 5 (depends on 4) The method as claimed in claim 4, wherein the comparison value is formed from values of the envelope curve following function and the minimum value function which apply at the same point in time. ### Claim 6 (depends on 5) The method as claimed in claim 5, wherein values of the minimum value function are determined at intervals which are greater in time by a multiple than the values of the envelope curve following function. ### Claim 7 (depends on 1) The method as claimed in claim 1, wherein a maximum magnitude of the audio signal is determined in order to form the envelope curve following function, from which maximum magnitude the envelope curve following function decays until the audio signal becomes greater again than the envelope curve following function, in this case the envelope curve following function following the audio signal until the maximum value is reached. ### Claim 8 (depends on 7) The method as claimed in claim 7, wherein the envelope curve following function decays exponentially. ### Claim 9 (depends on 1) The method as claimed in claim 1, wherein the audio signal is subjected to full-wave rectification before the formation of the envelope curve following function. ### Claim 10 (depends on 9) The method as claimed in claim 9, wherein the threshold value is varied dynamically as a function of the audio signal. ### Claim 11 (depends on 10) The method as claimed in claim 10, wherein the threshold value has an element with a constant value as the minimum value. ### Claim 12 (depends on 10) The method as claimed in claim 10, wherein a variable element of the threshold value is formed by a decay function which decays from a value which is set, in response to a prior start of note signal, to the amplitude of the envelope curve following function or of a value which is proportional thereto. ### Claim 13 (depends on 12) The method as claimed in claim 12, wherein the decay function decays to half its value in a range from 200 to 600 ms. ### Claim 14 (depends on 1) The method as claimed in claim 1, wherein a filter envelope curve following function and a filter minimum value function are formed from a low-pass-filtered audio signal. ### Claim 15 (depends on 14) The method as claimed in claim 14, wherein a positive and a negative envelope curve following function are formed initially, and the filter envelope curve following function is formed from the sum of the positive and negative envelope curve following functions. ### Claim 16 (depends on 14) The method as claimed in claim 14, wherein a comparison value is determined from the filter envelope curve following function, the start of a note being defined only when the filter envelope curve following function likewise shows a predetermined rise. ### Claim 17 (depends on 16) The method as claimed in claim 16, wherein the end of a note is defined when the value of the filter envelope curve following function is less than the value of the filter minimum value function or of a value proportional thereto at a point which is earlier in time by a predetermined interval. ### Claim 18 A method for recognition of the end of a note in the case of percussion or plucked musical instruments, comprising the steps of: providing a low-pass-filtered audio signal from the musical instrument; forming a filter envelope curve following function and a filter minimum value function from the low-pass-filtered audio signal, the forming step comprising forming a positive and a negative envelope curve following function and forming the filter envelope curve following function from the sum of the positive and negative envelope curve following functions, and providing an end of the note signal when the value of the filter envelope curve following function is less than the value of the filter minimum value function or a value proportional thereto at a point which is earlier in time by a predetermined interval. ### Claim 19 Apparatus for recognition of the start of a note of a musical instrument producing a sound which is represented by an audio signal varying in time, said apparatus comprising: (a) means for generating an envelope curve following function for said audio signal; (b) step detector means for detecting an upward step having a certain magnitude in said envelope curve following function; (c) threshold generator means for generating a threshold; (d) trigger means for outputting a note-start signal, if said magnitude of said detected upward step exceeds said threshold. ### Claim 20 (depends on 19) The apparatus according to claim 19, wherein said step detector means include (a) minimum value function generator means generating a minimum value function on the basis of said envelope curve following function; (b) comparison value generating means generating a comparison value which is indicative of a degree of deviation between a current value of said minimum value function and a current value of said envelope curve following function. ### Claim 21 (depends on 19) The apparatus according to claim 19, wherein said means for generating an envelope curve following function generates said envelope curve following function according to the following algorithm: each time a current value of said audio signal is larger than a current value of said envelope curve following function said envelope curve following function is increased up to said current value of said audio signal and decays otherwise. ### Claim 22 (depends on 19) The apparatus according to claim 19, wherein said threshold generator means generates a threshold having a first component which is constant in time and a second component which decays. ### Claim 23 (depends on 22) The apparatus according to claim 22, wherein said second component of said threshold decays starting from a value which is set, on the detection of a start of a preceding note, to the amplitude of said envelope curve following function or a value which is proportional thereto. ### Claim 24 (depends on 19) The apparatus according to claim 19, wherein said means for generating an envelope curve following function include rectifier means for subjecting said audio signal to a full-wave rectification. ### Claim 25 (depends on 20) The apparatus according to claim 20, wherein said means for generating an envelope curve following function include filter means for filtering said audio signal, from which filtered audio signal a filter envelope curve following function is formed in said means for generating an envelope curve following function and a filter minimum value function is formed in said minimum value function generator means. ### Claim 26 (depends on 25) The apparatus according to claim 25, wherein said means for generating an envelope curve following function form a positive and a negative envelope curve following function, said filter envelope curve following function being formed from the sum of said positive and negative envelope curve following functions. ### Claim 27 (depends on 25) The apparatus according to claim 25, wherein said comparison value generating means generates a comparison value between the value of said filter envelope curve following function and the value of said filter minimum value function or a value proportional thereto at a point which is earlier in time by a predetermined interval, said comparison value being indicative of the end of a note. ### Claim 28 (depends on 27) The apparatus according to claim 27, wherein the end of a note is defined when said value of said filter envelope curve following function is less than said value of said filter minimum value function or of said value proportional thereto at said point which is earlier in time by said predetermined interval.