©2008 League of Researchers in Nigeria JOLORN VOL. 9 No.11, June, 2008 I SSN 1595-532X All Rights Reserved ________________________________________________________________
MUSIC TECHNOLOGY - DIGITIZATION OF PERCUSSIVE RHYTHMIC PATTERNS FOR EFFECTIVE DESIGN OF SOFTWARE SEQUENCERS E. J. Garba Department of Mathematics and Computer Science Federal University of Technology P.M.B. 2076 Yola, Adamawa State. E-mail:
[email protected]; : 08036943881, 08088389044 ______________________________________________________________________________________
Abstract Nowadays, musical composition and rhythm generation is possible because most of the music applications use mathematical models such as combinatorial systems, grammars, probabilities and fractals to create new pieces of music . Other systems apply standard Genetic Algorithm procedures for evolving musical materials such as melodies, rhythms, chords, and so on. This paper sheds more light on the process of digitization of rhythmic patterns (of percussive instruments, such as drums) from standard music notations. It will also provide music software developers with the basic algorithmic concepts for designing and developing virtual studios and software sequencers.
______________________________________________________________________________ assigned to one beat. There are so many types INTRODUCTION of meters, but the common [C] time signature Music is the alternation of sound and silence. is 4/4 (i.e. four beats in a measure, and each When musicians play instruments, sound is beat is a quarter note). See the following table produced as the sound-producing parts of the for more details ((Garba 2003), (Garba 2007a)). instruments vibrate/oscillate. These vibrations Note Type Note Rest Number of cause air molecules to displace one another in symbol symbol Notes/Rests a systematic continuous flow, which moves Whole 16 away from its source. In the end, our ears perceive these air pressure fluctuations as Half 8 sounds that are translated by our brains as music (Garba 2003). Quarter 4 Musically speaking, the sounds produced are musical notes and the silences/pauses between the notes are called rests. The musical notes and rests vary in duration. That is, a note could be played for a long or short time. Thus, in contemporary music, there are six types of notes – whole, half, quarter, eighth, sixteenth and thirty-second. For proper interpretation of notes/rests duration, a piece of music is divided into portions called measures (bars). Each measure is bounded by two bars – within which a fixed number of notes/rests are required ((Garba 2003), (Garba 2007a)). To determine the number of notes/rests in a measure, a time signature (also known as meter) is required. This is usually placed in front of a musical staff. The time signature is a fractional number written in front of any musical piece. The numerator indicates the number of beats in a measure, while the denominator specifies the type of note/rest
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Eight
2
Sixteenth
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The combinations of notes/rests of varying durations make up the musical element called rhythm. In any musical composition, it determines the flow, the movement, the feel and possibly the speed of the music through time. Any rhythm is made up of beats or pulses, which form its pattern. In standard music (rhythm) notation, beats are represented by notes of different durations (whole, half, quarter, eighth, sixteenth, and 32nd notes). Concisely, a rhythm pattern is a sequence of strokes (taps) regardless of the pitch (it is the melody that is concerned with change in pitches/tones of the notes through time) (Garba 2007b).
Music Technology - Digitization of Percussive Rhythmic Patterns for Effective Design of Software Sequencers: E.J. Garba ________________________________________________________________________________________________
Rhythmic Patterns Digitization In order to program and realize the aforementioned musical concepts, a patternbased sampling approach is first applied to discover algorithm to an extant musical piece to reveal patterns at various levels of abstraction (Conklin 2007). Therefore, these concepts must be logically expressed via the binary number system. The simple logic here is this: when a musician plays a note, the binary number is 1; and when he doesn’t, the binary number is 0. Thus, using the common time signature [4/4], a measure will contain 16 binary digits (bits). This means that a whole note binary value will be 1000 0000 0000 0000. See the following table for more details. Note Type Whole Half Quarter Eight Sixteenth
Note Binary Value 1000 0000 0000 0000 1000 0000 1000 10 1
Rest Binary Value 0000 0000 0000 0000 0000 0000 0000 00 0
Therefore, these binary values, translated from standard music notations, initiate the process of digitizing rhythmic patterns (Vassilev, et al. 2007). In the same vein, it is possible to generate the same binary values from standard drum/percussion tablature. Note that Drum tablature (TAB) is a type of drum notation, where signs (symbols), numbers and letters (ASCII characters) are used instead of the musical notes. Thus, it indicates neither the pitch nor the duration of the note. However, notes (whole, half, quarter, eighth, sixteenth) are represented by the number of spaces between them. In this case, however, the dash symbol “–“ is used to represent a sixteenth note (Garba 2007). See the following tablature.
In the light of the above, the following rhythm will have a binary value of 1000100010101000 1010101010001000. Therefore, it means a measure can produce up to 65,536 [216] rhythmic patterns. Melodic patterns are created once each note is assigned a pitch according to the scale. Note that a single rhythmic pattern could produce several melodies; in the same vein, a particular melodic pattern could be varied to produce new rhythms. However, one of the drawbacks of this binary representation of rhythms is that information such as the intensity/dynamics and articulation/duration of each note are not precisely taken into account. Nevertheless, this representation is still useful for the initial generation of rhythmic patterns (Gimenes, et al. 2007). The digitization of the following music/drum notation (Hi-Hat, Snare, Bass Drum) will look like this: Hi-hat
1010101010101010
Snare
0000100010001000
Bass Drum
1000000000100000
Design Challenges of Software Sequencers Sequences have become the basic building blocks in contemporary music composition. Instead of composing music from the scratch, all you need is a sequence with at least one note (in case of drumbeats, cymbals, percussions and other rhythm instruments) or several notes (in case of melodic instruments, such as the guitars, piano etc). Traditionally, these sequences are stored on devices known as sequencers. Early sequencers were electronic devices, which composers used to create music from phrases of various musical instruments. But since the advent of digital audio, both hardware and software are used as sequencers. Cost effectiveness and flexibility of use are responsible for the increase in the popularity of software sequencers ((Garba 2003), (Garba 2007b)). The major challenge in designing these sequencers is how to produce sounds from these digitized rhythmic patterns (as discussed earlier on). There are quite a number of issues to be considered: Sequences – the nature of the sequences will
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JOLORN VOL. 9 No.11, June, 2008 ________________________________________________________________ determine how the sounds would be produced. There are basically three sources of digital audio: beeps, MIDI banks and sampled audio. However, generating beeps from the soundcard is least effective in digital audio production because of its monophonic nature. Therefore, the best option is using the MIDI sound bank or sampled audio sound bank (which contains notes in small wave files).
sequencers; therefore, the design stage of the sequencers should make provisions for this.
Musical concepts – Most importantly, some basic musical parameters must be included in the sequencer. To determine the length of the rhythm track, bars/measures are required. The meter/time signature helps in the proper interpretation of standard music notations. The tempo describes how fast the musical piece Memory vs. Hard disk playback – another would be played (i.e. how many beats per interesting challenge is the location of the minute). This parameter is very important sound sources (sequences) during playback. If because if, for instance, you slow down (or the sequences are stored on the hard disk speed up) a rhythm, it gives you an impression during playback, there would be more RAM that different notes were used instead of the available for smoother system performance; original. In other words, a pattern of whole but this will result in constant disk thrashing notes, if sped up twice, will sound like a half(Garba 2007c), as the sequences have to be note pattern (Garba 2007a). Finally, there be provisions for applying loaded from the hard disk all the time. It should should also be noted that intense I/O activity dynamics/accents to the notes of the rhythm. It degrades system performance, as the CPU is this parameter that is responsible for becomes highly preoccupied (more especially techniques, such as crescendo, flams, if the DMA mode of the hard disk is not grace/ghost notes etc. enabled) (Garba 2003). On the other hand, loading all your sequences into the RAM CONCLUSION implies having less memory available. Digitization of rhythmic patterns provides the basis for designing new software sequencers. Symphony of sounds –note that many Sequencers complement the efforts of the sounds/sequences would be played musicians in digital audio production and also simultaneously. It means, therefore, the help in better understanding of musical sequencer should be able to handle polyphony composition concepts in the virtual playback. The design stage should consider environment. multithreading during implementation. REFERENCES Effects and Processors – effects are primarily designed to modify the sound signal. The Conklin, Darrell (2007): Music Generation resulting sound, however, is the mixture of the from Statistical Models, Department of original sound (known as the dry signal) and Computing, City University, London, UK the modified sound (known as the wet signal). (http://www.soi.city.ac.uk/~conklin/papers/ais Most classical effects include Echo/Delay, b03.pdf). Reverb, Flanger, Chorus, Phaser and Pitch Shifters. Processors, on the other hand, modify Cope, D. (1991): Computers and Musical any signal that passes thru them. It means, Style, Oxford University Press, Oxford, UK. therefore, that in the end only wet signals are produced; that is, the sonic quality/character of Dodge C. and Jerse, T. (1985): Computer the original sound is totally changed. Examples Music, Schimer Books, London, UK. of processors are Equalizer (EQ), Distortion (Drive/Fuzz), Compressor, Limiter, Expander, Garba, E. J. (2003): Computer Music – Gate, Harmonic Exciter, Panner, Stereo Imager Rhythm Programming, Processing and and Noise Reduction (Garba 2007b). Note that Mastering, Trafford Publishing, Canada. application of effects/processors is a norm in
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Music Technology - Digitization of Percussive Rhythmic Patterns for Effective Design of Software Sequencers: E.J. Garba ________________________________________________________________________________________________
Garba, E. J. (2007a): Beats Sequencing with FL Computing, Communications And Electronics, University Of Plymouth, UK. Studio, Audiophilia Records Nigeria. Garba, E. J. (2007b): Digital Audio Production Stan Vassilev, Didier Dambrin & Scott Fisher & Music Technology (An introductory guide), (2005): FL STUDIO 6 Reference Manual, Image Line Software BVBA, Belgium. Audiophilia Records Nigeria. Garba, E. J. (2007c): Music Arranging & Worral, D. (2001): “Studies in metamusical Mixing with Reason, Audiophilia Records methods for sound image and composition”, Organised Sound, vol. 1, no. 3, pp. 183–194. Nigeria. Marcelo Gimenes, Eduardo Reck Miranda & Chris Johnson (2007): On The Learning Stages of an Intelligent Rhythmic Generator, Computer Music Research, School Of
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Xenakis I. (1971): Formalized Music: Thought and Mathematics in Composition, Indiana University Press, Bloomington (IN), USA.
