EP0035621B1 - Apparatus for the identification and indication of notes generated by a musical instrument - Google Patents

Description

The present invention relates to an apparatus for indicating notes emitted by means of an instrument.

By instrument is meant here any stringed or wind musical instrument, the human voice, or any device producing a sound emission.

It is known that instruments, and in particular stringed instruments, require frequent adjustments following variations in temperature or hygrometry, or due to the hysteresis of tension forces. The adjustment can only be made by comparing the sound emitted with a standard note (tuning fork) or, more simply by listening to the sound. This, however, requires considerable experience and a particularly skillful "ear".

Various devices have already been proposed for tuning musical instruments by measuring the frequency of the sounds emitted by means of these instruments.

Such an apparatus is described in German patent application DE 1547594. This known apparatus includes a calculating unit for making the difference between a digital value representative of the frequency of the note to be checked and a reference digital value selected from a memory in form of diode array by action on a keypad. The calculated difference is displayed, along with its sign. With such a device, it is therefore necessary to intervene manually to select a new reference value each time a note must be checked. This makes using the device difficult.

Another known device is described in German patent application DE 2716910. With this device, the frequency of the note to be checked is measured and displayed in digital form, by counting the number of oscillations during a reference period of approximately one second. Such a reference period is relatively long. In addition, displaying the result in the form of a numerical value requires a mental note-frequency or frequency-note conversion.

The present invention aims to provide an apparatus which allows, quickly and without the need for maneuvers, to display in clear any note produced by means of an instrument or, more precisely, to display in clear the exact note closest to the sound produced by the instrument with an indication of the situation of the sound produced in relation to the note displayed.

The present invention also aims to provide an apparatus which can be used by novice or even experienced musicians to control the adjustment of their instrument or to control the accuracy of the notes they produce with this instrument.

Another object of the present invention is to provide a device which is relatively inexpensive, which offers no difficulty in use, and to which it is possible to add, at very little cost, additional functions useful for learning. the use of a musical instrument.

These objects are achieved by means of an apparatus as defined in claim 1.

The use of a microprocessor with a memory constituting a table of notes in which all the identifiable notes are recorded makes it possible to obtain a clear display of the note to be identified, and this quickly and without any particular operation.

Advantageously, the calculating device comprises means for evaluating the difference between the calculated frequency of the sound to be identified and the frequency of the closest note read in the table and developing precision information as a function of this difference, and the means of the display are arranged to receive said precision information and display it.

This precision information is for example displayed in the form of a +, -, or 0 sign depending on the sign and the absolute value of the difference between the calculated frequency and the frequency of the note displayed.

According to a particular feature of the apparatus according to the invention, it comprises means for selecting time and measurements connected to the calculation device, the latter comprising means for counting pulses supplied by a time base and for supplying a signal trigger at the end of each selected time and each measurement, and indicator means are connected to the calculation device to indicate the times and the measurements in response to the trigger signals.

Taking advantage of the resources of the microprocessor and its associated circuits, this gives the device an additional metronome function.

The indicating means may consist of luminous indicators of different colors for the beats and the measures, or in sound indicators of different tones for the beats and the measures. In the latter case, the sounds produced are advantageously notes of the scale, which offers a possibility of self-test by simultaneously operating the sound indicators and the means for displaying the note produced by these indicators.

According to another feature of the apparatus according to the invention, the calculating device comprises a chord table in which information representing predetermined combinations of several notes is recorded.

This gives another additional function to the device by memorizing scales, arpeggios and chords useful for learning music theory, tones, intervals and harmony.

• - la fig. 1 est un schéma général d'un mode de réalisation de l'appareil selon l'invention,
• - la fig. 2 est un schéma plus détaillé du circuit d'entrée de l'appareil de la fig. 1, et
• - les fig. 3 à 5 sont des organigrammes relatifs à différentes opérations réalisées au moyen du microprocesseur de l'appareil de la fig. 1.

Other particularities and advantages of the apparatus according to the invention will emerge on reading the description given below, by way of indication but not limitation, with reference to the attached drawings in which:

• - fig. 1 is a general diagram of an embodiment of the apparatus according to the invention,
• - fig. 2 is a more detailed diagram of the input circuit of the apparatus of FIG. 1, and
• - figs. 3 to 5 are flowcharts relating to different operations carried out by means of the microprocessor of the apparatus of FIG. 1.

The sounds to be identified are transformed by means of a microphone 15, into electrical signals applied to an input circuit 10 comprising an amplifier 11, an energy detector 12 and a filtering circuit 13. The output signal from the filtering is applied to a computing device 20.

The computing device 20 comprises a microprocessor 21, memories 22 with direct access or RAM, read-only memories 23, or ROM, an input interface circuit 24, an output interface circuit 25 and receives pulses d '' a time base or clock 26.

At each period of operation of the microprocessor (for example 200 ms), the frequency of the output signal of the detector is calculated and is transferred to a RAM memory of the computing device. Then, the frequency note closest to that which has been calculated is sought in a 23a of the read only memories 23 which contains in the form of a table of notes all the notes identifiable by the apparatus in the different octaves. The calculation device also works out the quantity e = Δf / f _n , Δf being the difference between the calculated frequency and that of the note found and controls the display of this note as well as a +, - or 0 sign depending on whether ε > ε _o > 0, ε <ε ' _o <0, or ε' _o ≤ε≤ε _o .
The quantities s _o and s' _o are predetermined precision threshold values. For example, we choose _o = 1% ets' _o = -1%.

This display is performed on a display device 27 connected to the output interface circuit 25 of the calculation device. The device 27 is for example constituted by an alphanumeric liquid crystal display device.

The apparatus shown in fig. 1 further comprises coding wheels 30 and 31 intended respectively for the selection of time and of measurements and connected to the calculation device via the input interface circuit 24. A frequency divider 32 receives the pulses clock of the time base 26 and is also connected to the computing device 20.

The coding wheels 30 and 31 are, for example, three in number and two respectively, each numbered from 0 to 9. As a guide, the time intervals can be graduated linearly from 40 to 208, the corresponding graduation 60 to 1 second, while each measure can contain up to 32 beats. The time intervals and the number of times per measurement are manually selected by action on the encoder wheels.

The pulses SI supplied by the frequency divider 32, which for example have a period of 1 / 300th of s, are counted by means of the calculation device 20, which produces a signal ST, each time the selected value of an interval time is reached and an SM signal, each time the selected value of a measurement is reached.

The signals ST and SM are received by indicator means 33 in order to mark the selected times and measures. These indicating means comprise amplifiers 34, 35 which receive the signals ST and SM respectively and amplify them. These amplified signals are applied, on the one hand, to respective light indicators 36, 37 of different colors and, on the other hand, to respective sound indicators 38, 39 of different tones. Switching means (not shown) are provided to activate the light indicators, the sound indicators, or both.

In response to each ST and SM signal, the light indicators produce a short light burst and the sound indicators produce a short duration sound. This gives the device a function of metronome, or generator of rhythms.

When the device is used with its “note display” function, times and measures are indicated by flashes of light alone.

Preferably, the sounds produced by the sound indicators are precise notes of the range, but different. Thus, the proper functioning of the device can be verified by a self-test procedure by activating simultaneously the functions “note display” and “metronome”, without any other emission of sounds.

It will also be noted that, thanks to the resources of the microprocessor, the selection of the values of the times and of the measurements can be carried out automatically, for example by programming rhythms having varied sequences.

It will also be noted that predetermined combinations of notes can be recorded in a chord table 23b, included in the read-only or live memories of the calculation device, each combination constituting a chord whose knowledge is essential for learning harmony.

The device then advantageously includes the possibility of executing a particular program for checking agreements.

The chord verification program comprises a phase which consists in determining and recording the successive notes of a chord executed by a musician and in determining whether the chord thus identified appears in the chord table 23b. The identified agreement is displayed on the device 27 if this agreement is among those prerecorded in table 23b. Otherwise, the display, for example, of the word "FAULT" is ordered.

The chord verification program can also be part of a more general chord sequence program, making it possible to control the execution of successive chords according to a predetermined sequence.

The structure and various functions of the apparatus have been described above in general. Embodiments of parts of this apparatus and programs for performing the various functions will now be described in more detail.

Fig. 2 represents an embodiment of the input circuit 10.

The signals produced by the microphone 15 are amplified by means of an amplifier 11 with automatic gain control in order to obtain amplified signals of constant amplitude. This compensates for the weakening over time of sound produced by a musical instrument such as, for example, the piano.

A circuit 14 for eliminating short pulses is connected at the output of the amplifier 11, the circuit 14 comprising for example a capacitor connected between the output of the amplifier and a reference potential (ground) terminal.

The output of circuit 14 is connected, on the one hand, to the energy detector circuit 12, and, on the other hand, to the filtering circuit 13.

The circuit 12 includes an integrator 12a for integrating the amplified received signal. The level of the signal at the output of the integrator 12a is compared with a predetermined threshold value, by means of a circuit 12b for example a flip-flop or a comparator, which produces a signal DE when this threshold is crossed. As will be seen below, the signal DE authorizes the operation of the calculation device 20 to identify the note received by the input circuit 10.

The filter circuit 13 is intended to eliminate the harmonics of the frequency of the received note. To this end, it includes low-pass filters 13a, 13b, 13c, 13d, 13e, the cut-off frequencies of which are the upper limit frequencies of the successive octaves, in the audible range - that is to say approximately 78 respectively. , 156, 311, 622, 1244 and 2488 Hz. Other filters can be added for the higher octaves.

The outputs of the filters 13a to 13e are connected, on the one hand, to respective threshold detectors 16a to 16th and, on the other hand, to signal inputs of respective analog AND gates 17a to 17th. A logic circuit 18 has inputs connected respectively to the outputs of the threshold detectors 16a to 16e, and outputs connected respectively to the control inputs of the doors 17a to 17e.

Each threshold detector 16a to 16e has for example a structure analogous to that of the energy detector DE. When the signal at the output of a filter exceeds the threshold of the corresponding detector, the latter produces a signal of high logic level (“1”) at the corresponding input of logic circuit 17. This selects the AND gate which corresponds to the lowest cut-off frequency low pass filter through which a signal of sufficient level passes. Thus, the harmonics of the received note in the upper octaves are eliminated.

To this end, the logic circuit 18 includes NAND gates 18a to 18th with two inputs. The gate 18a has an input at logic level 0 and its other input connected to the output of the detector 16a. The gate 18b has its inputs connected to the detectors 16a and 16b and so on up to the gate 18th whose inputs are connected to the detectors 16d and 16th.

The outputs of AND gates 17a and 17e are joined by an analog OR gate 19. The output signal from gate 19 constitutes the input signal SE for the calculation device 20.

Fig. 3 shows the general organization of the software used for the implementation of the calculation device, the various programs used being recorded in program memories forming part of the read only memories 23.

• - programme «métronome» pour l'indication de temps et mesures prédéterminées,
• - programme «détermination et affichage des notes simples»,
• - programme «recherche et affichage des accords» pour rechercher si un accord joué figure dans la table des accords.

After the classic system initialization phase, at least one of the following programs is implemented:

• - "metronome" program for the indication of time and predetermined measures,
• - program "determination and display of single notes",
• - “search and display of chords” program to search if a chord played is in the chord table.

It will be noted that the “metronome” and “determination and display of single notes” programs can be implemented simultaneously. In addition, the program "search and display of chords" includes most of the program "determination and display of single notes".

• - test de présence de DE: il s'agit de vérifier la présence du signal DE indiquant qu'un niveau suffisant d'énergie est reçu
• - si DE est reçu, la fréquence f_i du signal SE converti sous forme numérique par le circuit d'interface 24 est mesurée; à cet effet, le nombre ni de passage à zéro du signal SE est calculé pendant une période donnée, par exemple 200 ms; chaque passage à zéro est détecté par un changement de signe de signal SE et la période de 200 ms est déterminée par comptage du nombre nécessaire d'impulsions de la base de temps; la valeur ni mesurée est mémorisée;
• - le calcul des paramètres d'entrée à la table des notes est effectué en fonction de la valeur ni mémorisée; la table des notes est organisée par octave et l'accès à cette table se fait par niveau d'octave, si la note se trouve suffisamment nettement à l'intérieur d'un octave, ou entre deux milieux d'octaves si la note se trouve à la limite de deux octaves; la procédure de calcul des paramètres d'entrée et d'accès à la table des notes est la suivante. On détermine d'abord quelle est l'octave concernée. Pour cela, la valeur mesurée de la fréquence f_; est divisée par un nombre prédéterminé constant K. La partie entière du résultat de la division constitue l'adresse d'une première table où l'on lit l'adresse d'entrée e_; de la partie de la table des notes à explorer. Avant d'effectuer l'exploration de la table des notes, on vérifie toutefois que le nombre correspondant à la fréquence f_i divisée par K n'est pas trop proche de la limite entre deux octaves. Si une différence d'au moins 9% est trouvée entre ce nombre et les limites d'octave, l'exploration
• - dans la table des notes est effectuée à partir de l'adresse e_i correspondant au début de l'octave concernée (exploration du premier type). Si une différence inférieure ou égale à 9% est trouvée, l'exploration dans la table des notes est effectuée à partir d'une adresse e_i - k correspondant au milieu de l'octave immédiatement inférieure (exploration du second type). L'exploration dans la table des notes est terminée lorsqu'a été déterminée la note Ni pour laquelle l'écart entre la fréquence exacte de cette note et la fréquence mesurée est minimal;
• - la note Ni est lue et mémorisée et la précision ε_i = (f_i-fN_i)/fN; est calculée, fN_i étant la fréquence exacte de la note N_i; la quantité ε_i est comparée à des valeurs prédéterminées positives et négatives ε_o et ε'_o (par exemple +1% et -1%) et l'on mémorise ε_i = 1, 0 ou -1 selon que
  ε_i>ε_o>0,-ε_o≤ε_i ≤ε_oouε_i<-ε_o<0;
• - la note Ni est affichée sur le dispositif d'affichage 17 accompagnée du signe +, 0 ou - selon que ε_i=1,0 ou-1;
• - ensuite, il y a retour en attente d'une nouvelle détection d'énergie à moins qu'une recherche d'accords soit demandée; cette dernière condition est vérifiée en contrôlant la valeur du signal RA, valeur commandée par exemple par actionnement d'une touche de l'appareil lorsque l'exécution du programme «recherche et affichage d'accords» est demandée.

We will now refer to the flow diagram of FIG. 4. For the “determination and display of single notes” program, the following operations are carried out:

• - DE presence test: check the presence of the DE signal indicating that a sufficient level of energy is received
• - if DE is received, the frequency f _i of the signal SE converted into digital form by the interface circuit 24 is measured; for this purpose, the number ni of zero crossing of the signal SE is calculated during a given period, for example 200 ms; each zero crossing is detected by a change in signal sign SE and the period of 200 ms is determined by counting the necessary number of pulses from the time base; the value ni measured is memorized;
• - the calculation of the input parameters to the note table is carried out according to the value neither stored; the note table is organized by octave and access to this table is by octave level, if the note is sufficiently clearly inside an octave, or between two mid-octaves if the note is found at the limit of two octaves; the procedure for calculating the parameters for entering and accessing the grade table is as follows. We first determine which octave is concerned. For this, the measured value of the frequency f _; is divided by a predetermined constant number K. The integer part of the result of the division constitutes the address of a first table from which the input address e is read _; of the part of the notes table to explore. Before exploring the table of notes, it is checked however that the number corresponding to the frequency f _i divided by K is not too close to the limit between two octaves. If a difference of at least 9% is found between this number and the octave limits, exploration
• - in the table of notes is made from the address e _i corresponding to the start of the octave concerned (exploration of the first type). If a difference less than or equal to 9% is found, exploration in the note table is carried out from an address e _i - k corresponding to the middle of the octave immediately lower (exploration of the second type). The exploration in the note table is finished when the note Ni has been determined for which the difference between the exact frequency of this note and the measured frequency is minimal;
• - the note Ni is read and memorized and the precision ε _i = (f _i -fN _i ) / fN; is calculated, fN _i being the exact frequency of the note N _i ; the quantity ε _i is compared with predetermined positive and negative values ε _o and ε ' _o (for example + 1% and -1%) and we memorize ε _i = 1, 0 or -1 depending on whether
  ε _i > ε _o > 0, -ε _o ≤ε _i ≤ε _o ouε _i <-ε _o <0;
• the note Ni is displayed on the display device 17 accompanied by the sign +, 0 or - depending on whether ε _i = 1.0 or -1;
• - then there is a return waiting for a new energy detection unless a search for agreements is requested; this latter condition is verified by checking the value of the signal RA, which value is controlled for example by pressing a button on the device when the execution of the program "search and display of chords" is requested.

It is assumed that the chords recorded in the chord table are combinations of two or three notes, the chord table being organized into a group of two note chords and a group of three note chords.

• - attente d'une note;
• - lorsqu'une première note N, est identifiée, et qu'il a été vérifié que l'on doit rechercher un accord, cette première note est enregistrée et le contenu d'un registre [NNI] (nombre de notes identifiées) est placé à 1, ce registre étant initialement mis à zéro;
• - on examine ensuite si un accord peut être recherché par examen du contenu du registre NNI;
• - le contenu du registre NNI étant égal à 1, on retourne en attente d'une autre note;
• - lorsqu'une seconde note N₂ est identifiée, elle est enregistrée et le contenu du registre [NNI] est incrémenté d'une unité (NNI = 2);
• - il y a alors possibilité de rechercher un accord dans la table des accords;
• - la recherche dans la table des accords est effectuée en comparant successivement chaque accord de deux notes de cette table avec le couple Ni-N₂, du fait de la vérification NNI = 2;
• - si l'accord N₁-N₂ est trouvé dans la table 23b, le registre [NNI] est remis à zéro et l'accord est affiché sur le dispositif d'affichage 27;
• - si l'accord N₁-N₂ n'est pas trouvé, la recherche est poursuivie parmi les accords de trois notes figurant dans la table; si aucun de ces accords ne comporte N₁-N₂ comme deux premières notes, le registre [NNI] est remis à zéro et le mot «FAUTE» est affiché sur le dispositif 27; par contre, si un des accords de la table commence par les notes N₁-N₂, on retourne en attente d'une troisième note;
• - lorsqu'une troisième note N₃ est trouvée, elle est enregistrée et le contenu du registre [NNI] est incrémenté d'une unité (NNI = 3);
• - la recherche dans la table des accords est effectuée dans le groupe des accords de trois notes seulement, du fait de la vérification NNI = 3;
• - si l'accord Ni-N₂-N₃ est trouvé, le registre [NNI] est remis à zéro et l'accord est affiché sur le dispositif d'affichage 27 (dont la capacité est, bien entendu, choisie suffisante à cet effet);
• - si l'accord Ni-N2-N3 n'est pas trouvé, le registre [NNI] est remis à zéro et le mot «FAUTE» est affiché sur le dispositif d'affichage 27.

The “search and display of agreements” program includes the following stages:

• - waiting for a note;
• - when a first note N, is identified, and it has been verified that a chord must be sought, this first note is recorded and the content of a register [NNI] (number of notes identified) is placed at 1, this register being initially set to zero;
• - we then examine whether an agreement can be sought by examining the content of the NNI register;
• - the content of the NNI register being equal to 1, we return waiting for another note;
• - when a second note N ₂ is identified, it is recorded and the content of the register [NNI] is incremented by one (NNI = 2);
• - it is then possible to search for an agreement in the table of agreements;
• - the search in the chord table is carried out by successively comparing each chord of two notes from this table with the Ni-N ₂ pair, due to the verification NNI = 2;
• - If the agreement N ₁ -N ₂ is found in the table 23b, the register [NNI] is reset to zero and the agreement is displayed on the display device 27;
• - if the chord N ₁ -N ₂ is not found, the search is continued among the chords of three notes appearing in the table; if none of these chords includes N ₁ -N ₂ as the first two notes, the register [NNI] is reset to zero and the word “FOUTE” is displayed on the device 27; on the other hand, if one of the chords of the table begins with the notes N ₁ -N ₂ , we return waiting for a third note;
• - when a third note N ₃ is found, it is recorded and the content of the register [NNI] is incremented by one (NNI = 3);
• - the search in the chord table is carried out in the chord group of three notes only, due to the verification NNI = 3;
• - if the Ni-N ₂ -N _{3 agreement} is found, the register [NNI] is reset to zero and the agreement is displayed on the display device 27 (the capacity of which is, of course, chosen sufficient for this effect);
• - if the Ni-N2-N3 agreement is not found, the register [NNI] is reset to zero and the word “FAULT” is displayed on the display device 27.

As already indicated above, this program can be completed by checking, not only that each chord played appears in the chord table but, moreover, that the chords are played in a predetermined order, in accordance with a recorded sequence.

• - incrémentation d'une unité du contenu [RI] d'un registre RI: [RI] + 1 - [RI];
• - lecture de la valeur T affichée par les roues codeuses 30 et convertie en nombre de périodes du signal d'interruption SI;
• - comparaison du contenu [RI] du registre RI avec la valeur T;
• - si [RI] < T, retour au programme interrompu;
• - si [RI] = T, incrémentation d'une unité du contenu [RT] d'un registre de temps RT: [RT] + 1 - [RT]
• - remise à zéro du registre RI = [RI] - 0;
• - lecture de la valeur M affichée par les roues codeuses 31;
• - comparaison du contenu [RT] du registre RT avec la valeur M;
• - si [RT] < M, production d'un signal de sortie de déclenchement ST et retour au programme interrompu;
• - si [RT] = M, production d'un signal de sortie de déclenchement SM, remise à zéro du registre RT jRTj -- 0, et retour au programme interrompu.

There is also shown in FIG. 4 the different operations of the metronome program. This program is for example implemented in response to the actuation of a particular key closing a switch interposed between the time base 26 and the frequency divider 32. The signal produced by the frequency divider 32 constitutes a signal of interruption which triggers the following operations:

• - incrementing the content [RI] of a RI register by one: [RI] + 1 - [RI];
• - Reading of the value T displayed by the encoder wheels 30 and converted into the number of periods of the interrupt signal SI;
• - comparison of the content [RI] of the register RI with the value T;
• - if [RI] <T, return to the interrupted program;
• - if [RI] = T, incrementing by one the content [RT] of an RT time register: [RT] + 1 - [RT]
• - reset register RI = [RI] - 0;
• - reading of the value M displayed by the encoder wheels 31;
• - comparison of the content [RT] of the register RT with the value M;
• - if [RT] <M, production of an ST trigger output signal and return to the interrupted program;
• - if [RT] = M, production of a trigger output signal SM, reset of register RT jRTj - 0, and return to the interrupted program.

Of course, various modifications and additions can be made to the embodiment described above of the apparatus according to the invention.

Thus, the calculation of the frequency f _i can be carried out by counting the number of pulses of the time base during a determined number of periods of the signal SE, each period being for example the interval between two passages by zero in the same successive meanings.

Furthermore, in the case of measuring relatively long sounds, it is possible to introduce a smoothing operation for the frequency measurement and a smoothing operation for the identification of the note.

en désignant par f_in-1 la fréquence lissée précédemment déterminée. En d'autres termes, on prend en compte une nouvelle valeur f, si elle diffère de la valeur précédente de plus de 3%, sinon on effectue la moyenne arithmétique entre cette nouvelle valeur et la valeur précédente.The frequency smoothing operation is inserted in the flowchart for finding and displaying single notes, before the calculation of the input parameters in the note table (calculation of f _{; /} K). We know that musicians share an octave in 12 semitone intervals, each semitone having 1.05946 times the frequency of the previous lower semitone, that is to say a frequency approximately 6% higher. The following smoothing process is then used: f _i being the frequency which has just been measured, the frequency is "smoothed" by giving it the value

by designating by f _in-1 the smoothed frequency previously determined. In other words, we take into account a new value f, if it differs from the previous value by more than 3%, otherwise we perform the arithmetic mean between this new value and the previous value.

The note smoothing operation is inserted before the display of the note and its precision. This operation consists in carrying out a majority test on the precision insofar as the note remains the same three successive times. The majority test consists in displaying - if the precision - is determined at least two times out of three, in displaying +, if the precision + is determined at least twice in three, and in displaying 0 if one has determined three times the precision 0 or once each precision +, - and 0. In the case where for a measurement of a sound, the same note is not obtained three successive times, it may be agreed to display the word "FOUL".

Claims (11)

1. Identification and indicator apparatus for notes produced by means of an instrument, said apparatus comprising an amplifier (11) for amplifying a signal representing a sound to be identified, a filtering circuit (13) connected to the output of the amplifier, a memory (23) in which are recorded items of information representing the music notes, a calculation device (20) connected to the memory (23) and to the output of the filtering circuit (13) to work out a value representative of the frequency of the sound to be identified, and display means (27) for displaying information representative of the calculated frequency, characterized in that the calculation device comprises a microprocessor (21) and memories (23a, 23b) connected to the microprocessor and comprising said note memory (23b); and in that a detector of energy (12) is provided so as to authorize the operation of the calculation device to identify and display one or more successive notes, and this as long as the energy of the sound to be identified exceeds a certain threshold, the reading of one item of information in said memory being controlled solely in relation to the measured value of the frequency of the sound to be identified, and the information read in said memory being transmitted to the display means (27) to display continuously in alphanumerical form the note closest to the sound to be identified and the octave in which said sound is situated.

2. Apparatus according to claim 1, characterized in that the calculation device comprises means for estimating the difference between the frequency of the sound to be identified and the frequency of the closest note read in the memory and for working out an information of accuracy depending on that difference, and this display means are arranged so as to receive said information of accuracy and to display it.

3. Apparatus according to claim 2, characterized in that said information of accuracy is displayed in the form of one amongst several signs indicating that the difference between the calculated frequency and the frequency of the displayed note is respectively, positive and of absolute value greater than a given threshold, or negative and of absolute value greater than a given threshold, or of absolute value less than a given threshold.

4. Apparatus according to any one of claims 1 to 3, characterized in that the filtering circuit comprises: a set of low-pass filters receiving the signal representing the sound to be identified, threshold gates connected to the output of the filters, gates having each a signal input connected to the output of a respective filter and a control input, and a selection circuit with inputs connected to the outputs of the threshold detectors and outputs connected respectively to the control inputs of the gates, to determine the low-pass filter with the lowest cut-off frequency through which passes at least part of the received signal, and to close the gates connected to the filters whose cut-off frequency is higher than that of the determined filter.

5. Apparatus according to any one of claims 1 to 4, characterized in that the energy detector comprises an integrator connected to the output of the amplifier.

6. Apparatus according to any one of claims 1 to 5, characterized in that it comprises means for selecting times and measures, connected to the calculation device, in that the calculation device comprises means for counting pulses supplied by a time base and for supplying a triggering signal at the end of each time and each measure selected, and in that indicator means are connected to the calculation device to indicate the times and measures in response to the triggering signals so as to constitute a metronome or rhythm generator.

7. Apparatus according to claim 6, characterized in that the indicator means comprise light indicators of different colors for the times and the measures.

8. Apparatus according to claim 6, characterized in that the indicator means comprise sound indicators of different tones for the itmes and the measures.

9. Apparatus according to claim 8, characterized in that the sounds produced by the sound indicators are notes from the scale.

10. Apparatus according to any one of claims 1 to 9, characterized in that the calculation device comprises a chord table in which are recorded information representing predetermined combinations of several notes.

11. Apparatus according to claim 10, characterized in that the calculation device comprises means for recording several notes identified successively, and for comparing the notes so recorded with the combinations appearing in the chord table so as to control the display of an indication relative to the result of such a comparison.

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