EP0734567B1 - Signal-analysis device with at least one tensioned string and a receiver - Google Patents

Abstract

Described is a signal-analysis device (1) with at least one tensioned string (E1, H2, G3, D4, A5, E6) whose oscillating length can be varied by pressing the string against at least one tie-bar, the device also having a receiver (2) and an evaluation unit (3 to 9) connected to the receiver. The aim of the invention is to provide a guitar synthesizer which provides the desired note data relatively rapidly after stimulation of the string. This is achieved by vertue of the fact that the evaluation unit (3 to 9) detects pulses or pulse groups which, following stimulation of the string (E1, H2, G3, D4, A5, E6), pass along the string past the receiver (2), the evaluation unit generating from the sequence of pulses or pulse groups a signal which represents a note.

Description

The invention relates to a signal analysis device with at least one string that is vibrating Length by contact with at least one bundle is changeable, with a transducer and with a evaluation device connected to the transducer.

Such a signal analysis device can also be used shortly called "guitar synthesizer".

There is an increasing trend in modern pop and rock music The tendency is no longer towards musical instruments directly used for sound or sound generation, but to produce only electrical signals or to analyze and implement that by computer or other circuits are processed further. To this There are standardized interfaces, of which purpose the MIDI interface has become relatively well known.

During such signal generation or analysis with keyboard musical instruments with relatively little difficulty is connected because here is a button exactly a pitch is assigned and the volume if necessary about the velocity of the key can be determined, prepares the signal analysis Stringed instruments, such as guitars, are considerable Difficulties. With such string instruments a basic note is assigned to each string. By Depress the string on different taps or The pitch of a plucked, struck can be fretted or a differently excited string. Around The first thing to do is to determine the correct pitch wait for such a tone to form and then the frequency or duration of at least one, preferably but measure several periods to pitch with the necessary reliability to find out can.

US-A-4 823 667 therefore shows a signal analysis device as an electronic musical instrument, the kind of Guitar is operated using a frequency analyzer the frequency of the excited string is provided determined. However, such an approach leads to timing problems. With a normal guitar the lowest tone has a frequency of around 80 Hz (exactly: 82 Hz), so that a full oscillation takes about 12.5 ms claimed. Since one is usually used for security reasons want to measure two vibrations to be reliable To come up with statements adds up the necessary Time already to 25 ms. This does not take into account that after stringing, e.g. by Plucking or beating, still needs some time, to get into the steady state. Therefor is usually also not to be neglected Time period to be set, which is quite double can be a period length, so that the desired Pitch information only available after 50 ms stands. A time delay of 50 ms is for but a musician is already clearly noticeable. It corresponds the installation of the loudspeaker in one Distance of about 15 m.

As an alternative solution to this problem US-A-5 085 119 has switches on the guitar neck provided that when depressing the corresponding String on the desired fret. The pitch information is then, however, just like with a keyboard instrument, no longer through the string vibration, but by depressing one Switch won. This makes playing considerably more difficult.

EP-A-0 227 906 shows an electronic string instrument like a guitar with an evaluation device to determine the pitch that occurs when playing through the guitar strings are created. The evaluation device is connected to two transducers. The one pickup serves to determine the vibration the string itself. As long as the string is swinging, is a Sound made. The other pickup has at the same time the function of a transmitter with which ultrasound pulses to be put on the string. The transit time of the ultrasonic pulses can be evaluated to provide information to win over the string length and thus the pitch.

EP-A-0 288 062 shows a similar musical instrument a signal analysis device in which the transducer arrangement also has an acoustic pickup, which determines the vibration of the string itself and an ultrasound arrangement, the ultrasound pulses couples onto the string and receives from there. The Time difference between sending and receiving the ultrasonic pulses provides information about the active string length.

The invention is based, with one Guitar synthesizers get the pitch information faster to be able to win.

This task is performed with a signal analysis device of the type mentioned at the outset in that the evaluation device Impulses or groups of impulses recorded after picking up the string by striking the String by a player on the string on the pickup walk past, and due to the chronological order of the Pulse or the pulse groups generates a signal that represents a pitch.

So you don't have to wait until you are on the string has formed a vibration, which is then measured rather, one evaluates so-called "plucking transients" off, i.e. impulses or pulse sequences that occur when excited the guitar string result. Becomes a guitar string plucked or struck are created in the simplest Fall two impulses or traveling waves that differ from the Excitation point in the direction of the clamping points to move the string or to where the string is depressed to the federal government. There they are reflected and run towards each other again. After a few The known standing then runs back and forth Wave out that is normally used for sound generation responsible for. You can now change the duration of this Measure or evaluate impulses on the string and from the term or the term difference between individual impulses the necessary information about the String length and tension and thus over the pitch win. Of course, in reality will not form individual impulses, but impulse groups. This however, does not change anything on which the invention is based Principle.

The evaluation device preferably also detects the Polarity of the pulses or pulse groups and determined from the temporal sequence of the impulses or impulse groups a signal that represents the excitation position of the string. The string's excitation position, i.e. the spot, on the string plucked or struck or on other way of moving is playing the guitar one of the outstanding design options for the player. Because you have two pulses or groups of pulses has available that is different from the stimulus position from in opposite directions on the Moving the string and with corresponding time delays at the respective clamping points of the strings can be reflected due to the different The duration of the impulses is also information win over where the suggestion was located. You get this information practically the same way quickly like the information about the pitch so that the determination of the excitation position is no further Delay means.

The evaluation device preferably has a neural one Network on that any sequence of pulses or pulse groups classified into one of a variety of classes. The consequences of impulses or impulse groups, that can be assigned to a certain pitch have essential similarities that a neural Network can be found relatively easily. You can here with similarities between the individual pulse sequences or satisfy sequences of impulse groups, without having to evaluate each pulse train exactly in time got to. The timely evaluation can occasionally to be difficult if the impulses not in the desired purity, but instead are surrounded by noise. In this case it can sometimes be difficult to get accurate start and finish End times for the measurement of the distances from individual Define impulses or impulse groups. A neural network, however, can be programmed that it is the decision which pitch is present and at what position the string has been excited, simply due to similarities. A neural network has the advantage that it is not necessarily explicit predetermined rules, according to which there are similarities judged. Rather, a neural network can be trained, i.e. by presenting a Plenty of examples with the right results it forms algorithms or control behavior itself from which it enables the following examples to be correct to classify. A neural network can also be used in to some extent also make generalizations, whereby it forms the rules for the generalizations themselves. The neural network is therefore capable of pulse trains or sequences of impulse groups even then relative to recognize exactly when the given pulse train not exactly with an already trained pulse train matches. Because neural networks usually use one Large number of processors working in parallel are fast enough to signal the pitch available in the required short period of time to deliver.

It is also preferred that the evaluation device has a Comparison device having a string Pitch signal obtained in the steady state with the signal obtained from the pulse sequence and in the event of a deviation that is a predetermined one Dimension exceeds a learning algorithm of the neural Triggers the network. The evaluation device limits the Pitch detection is therefore not based on the evaluation of the "Plucking transients". Rather, this evaluation is only the beginning, however, which enables the pitch signal to be made available within a very short time. The evaluation device also monitors whether that recognized signal with the later in the swinging String forming pitch matches. Is this the Case the "prediction" was correct and there are none further measures necessary. Was the "prediction" however wrong, there is a certain probability of it before that the algorithm according to which the neural Network that assessed the similarity was faulty. In in this case the result of the comparison can be used be another training example to the neural network to provide. Using this training example can learn the neural network again and improve its detection algorithm.

The neural network is preferably a selection device upstream, the individual from a pulse group Selects impulses. This is especially true of Advantage if the neural network is limited Provides work capacity. In this case the amount of information, that the neural network has to process, keep smaller.

There is preferably a separate pickup for each string intended. This allows a parallel sound signal generation for every string without it due to the different picking transients for all strings, So the back and forth impulses Irritation of the evaluation device can occur.

Fig. 1

eine schematische Darstellung einer Signalanalyseeinrichtung,

Fig. 2

einen schematischen Aufbau einer Saite und

Fig. 3

eine schematische Darstellung eines Signalverlaufes.

The invention is described below with reference to a preferred embodiment in conjunction with the drawing. Show here:

Fig. 1

1 shows a schematic representation of a signal analysis device,

Fig. 2

a schematic structure of a string and

Fig. 3

a schematic representation of a signal curve.

A signal analysis or generation device 1 has six strings E1, H2, G3, D4, A5 and E6 on the after Kind of a guitar. For every string is a sensor 2 is provided, for example as electromagnetic or piezoelectric pickups can be trained. The transducers 2 are with one Analog / digital converter 3 connected in the illustrated Embodiment for each transducer 2 one Has channel, that is six channels.

The analog / digital converter 3 is with a microprocessor 4 connected to the input and output management accomplished for a neural network 5. Between the microprocessor 4 and the neural network 5 can a selection device 6 may also be provided, whose function will be described later.

Furthermore, the analog / digital converter 3 with a frequency meter 7 connected. The frequency meter 7 and the Microprocessor 4 are with a comparison device 8 connected. The comparison device 8 is with a MIDI interface 9 connected. The comparison facility 8 is also connected to the neural network 5 with a learning input 10.

The neural network 5 receives, managed by the microprocessor 4 and possibly prepared by the Selector 6, a sequence of pulses or groups of pulses and classifies these episodes into one of a variety of specific classes. Every class allows a statement about the pitch and if necessary also about the excitation position of the string, as explained below.

Fig. 2 shows schematically a string 11 which between a fixed clamping point 12 and a clamping point 13, on which the voltage is adjustable, clamped is. The string 11 spans a guitar neck 14 the different frets 15 are arranged. Through a Arrow 16 shows a fret on which the string 11 is depressed. This bundle 16 determines together with the clamping point 12 the effective length of the string 11. The responsible pickup 2 is arranged under the string.

By a triangle 17, which is a guitar pick or the like Plucking tool should symbolize is an excitation position shown for string 11. If so the string 11 plucked at this stimulation position or is struck, does not immediately arise standing wave at the frequency required for the pitch is characteristic. Rather, a settling process begins, which describes itself in a simplified way leaves that from the excitation position two pulses 18, 19 run left and right. These impulses or traveling waves are indicated by a 1 and drawn 2 different from each other. Of the Pulse 18 now runs to the left up to collar 16 the string is held down. There he is under Phase rotation reflects and runs back again. In in the same way, pulse 19 runs to the right to the clamping point 12 where it reflects with phase shift and runs back again. The back and forth Impulses or waves overlap and reproduce the known standing wave with which the string 11 vibrates.

However, the pulses 18, 19 run on the transducer 2 past. A corresponding time diagram is in Fig. 3 shown. It can be seen here that the first Impulse, which should have a positive amplitude, too at a time t1 crosses the transducer while its reflection, now with a negative amplitude, too at a time t2 crosses the sensor. To a Time t3 reaches that reflected at the clamping point 12 second pulse the transducer as it closes the sensor 2 again overflows at a time t4. This is the second time, namely at Bund 16 reflected second impulse. At times t5 and t6 runs the first pulse again, which then at the clamping point 12 or the federal government 16 has been reflected, via the transducer 2 and at times t7 and t8 the second impulse, which is then again at the clamping point 12 or the federal government 16 has been reflected.

The movement or walking speed of the pulses 18 or 19 on the string 11 is known. You can now determine the active length of the string 11 from the time difference T1, which is the distance between the times t5 and t1, with the aid of this traveling speed. But this is also the length that is responsible for the pitch of the string 11. If the distance between the transducer 2 and the collar 16 or the collars 15 is known, the distance T ₂ would in principle also be sufficient, that is the distance between the times t2 and t1. This gives you the option of fine-tuning because the guitarist can slightly vary the pitch by slightly shifting his finger on frets 15, 16. In addition, in many cases the pulses cannot be distinguished as clearly as is shown in FIG. 3 for the sake of simplicity. Rather, the individual impulses may become blurred and smeared, in particular if, when plucking or striking the string 11, it is not individual impulses, as shown, but entire groups of impulses.

In almost all cases, however, the position of the excitation can be deduced from the time difference T ₃ , namely from the difference between the times t3 and t1. If the string length is known from the difference T1, the difference T3 can be used to calculate backwards at which fraction of the string the excitation took place.

However, the time measurement is used to determine the distance the impulses shown occasionally with uncertainties charged. For this reason, the Sequence of pulse groups, which is detected by the transducer 2 with the help of the selection device 6 individual Selected pulses that are fed to the neural network 5 will. The neural network can have similarities recognize between individual sequences of impulse groups and the "plucking transients" caused by these pulse trains are represented, so classify their assignment to individual classes, each a pitch and reproduce an excitation position with great certainty is possible. The recognition process is carried out by triggered pulses. The successive positive and negative impulses or impulse groups are forwarded to the neural network, that tries every time to record the pattern or the recorded sequence of a previously learned sequence assign. This process is repeated until either the neural network produces a positive result or the frequency meter 7 has the corresponding Has provided information. As long as the neural Network is still in the learning or training phase in many cases the frequency meter 7 will be faster. After a certain training phase, the neural Network 5, which the rules for detection when appropriate Programming can form itself, but sufficient Information saved to the classification to be able to make it extremely effectively. The neural network 5 also forms certain rules for generalizations, so that patterns not actually learned can be recognized if these have certain similarities to the already learned examples.

Since the frequency meter 7 has a pitch detection in parallel is also during the operation of the signal analysis device 1 further learning possible. The Comparison device 8 compares that by the neural Network 5 determined pitch with a later determined the frequency meter 7. Here, on the one hand understand the fine pitch changes on the other hand errors can be avoided with this procedure or discover and eliminate inaccuracies in the algorithm, which the neural network 5 uses. The comparison facility 8 namely couples the determined Error back into the neural network 5 and triggers one new learning algorithm so that the same error not because of the improved recognition option can occur once. If there is no difference, gives the comparison device 8 or the signals continue unchanged to the MIDI interface 9.

The output results of the neural network are like this further processed that the MIDI interface 9 MIDI signals which can provide a MIDI synthesizer or control an expander module. The pitch coded in the MIDI signal corresponds to the Pitch of the guitar string. Furthermore, in the MIDI signal as control information the plucking position as coded Sound character may be included.

Claims (6)

1. Signal analysing device (1) including at least one tensioned string (11) whose vibratile length is alterable by pressing it onto at least one fret (15), and also including a transducer (2) and an evaluating device connected to the transducer (2), characterised in that the evaluating device detects pulses or groups of pulses in the form of plucked transients running along the string (11) past the transducer (2) after the string (11) has been excited by the player striking the string, evaluates the transit time of the pulses on the string and produces a signal representing a pitch on the basis of the transit time or the difference in transit times between individual pulses or the groups of pulses (Fig. 3).
2. Device in accordance with Claim 1, characterised in that the evaluating device also detects the polarity of the pulses or groups of pulses and establishes a signal representing the excitation position (17) of the string (11) from the time sequence of the pulses or the groups of pulses.
3. Device in accordance with Claim 1 or 2, characterised in that the evaluating device comprises a neural network (5) which classifies each sequence of pulses or pulse groups into one of a plurality of classes.
4. Device in accordance with Claim 3, characterised in that the evaluating device comprises a comparison device (8) which compares a pitch signal derived from the string (11) in its steady state with the signal derived from the sequence of pulses and initiates a learning algorithm for the neural network (5) when a deviation exceeding a predetermined value occurs.
5. Device in accordance with Claim 3 or 4, characterised in that a selection device (6) which selects individual pulses from a group of pulses is connected prior to the neural network (5).
6. Device in accordance with any of the Claims 1 to 5, characterised in that a separate transducer (2) is provided for each string (11).

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