00001 #include "MusimatTutorial.h" 00002 MusimatTutorialSection(B0203) { 00003 Print("*** B.2.3 Tempo ***"); 00004 /***************************************************************************** 00005 00006 B.2.3 Tempo 00007 00008 In common music notation, tempo is expressed using Mälzel's metronome markings (see sec- 00009 tion 2.6.2). For example, Q = 60MM indicates that the beat or pulse of the music is associated 00010 with quarter notes and that there are 60 beats per minute. Thus at Q = 60MM each quarter note 00011 lasts 1 second, and at Q = 120MM each quarter note lasts 0.5 second. Thus tempo scales the 00012 durations of rhythms. 00013 00014 We can emulate this by calculating a tempo factor based on Mälzel's metronome markings. 00015 Rhythms are then multiplied by this coefficient to determine their actual duration. First, we need 00016 a function that calculates the tempo factor: 00017 *****************************************************************************/ 00018 00019 para1(); // Step into this function to continue the tutorial 00020 } 00021 00022 Real mm(Real beats, Real perMinute) { 00023 Return(1.0 / (4.0 * beats) * 60.0 / perMinute); 00024 } 00025 00026 Static Void para1() { 00027 00028 /***************************************************************************** 00029 The beats argument is the rhythmic value that gets the beat, and the perMinute argument is the 00030 number of beats per minute. For example, 00031 *****************************************************************************/ 00032 00033 Real tempoScale = mm( Duration(Quarter), 60.0 ); // 60 quarternotes per minute 00034 00035 /***************************************************************************** 00036 sets tempoScale to 1.0, and 00037 *****************************************************************************/ 00038 00039 tempoScale = mm(Duration(Quarter), 120.0); // 120 quarternotes per minute 00040 00041 /***************************************************************************** 00042 sets tempoScale to 0.5. Scaling a list of rhythms with tempoScale adjusts them to the pre- 00043 vailing tempo. Start with a rhythm list. 00044 *****************************************************************************/ 00045 00046 RhythmList T(Quarter, Eighth, Eighth, Eighth, Sixteenth, Sixteenth, Quarter); 00047 Print(T); 00048 00049 /***************************************************************************** 00050 prints {(1,4), (1,8), (1,8), (1,8), (1,16), (1,16), (1,4)}. Now scale it. 00051 *****************************************************************************/ 00052 00053 RhythmList S = T * tempoScale; // tempoScale == 0.5 00054 Print(S); 00055 00056 /***************************************************************************** 00057 prints {(1,8), (1,16), (1,16), (1,16), (1,32), (1,32), (1,8)}. 00058 00059 Though this explicit approach to managing tempo works fine, in fact Rhythm() has this cal- 00060 culation conveniently built in. It works in conjunction with a built-in function named Set- 00061 Tempo() that implicitly scales all rhythmic durations by the specified tempo factor. So, for 00062 example, given the preceding definition of RhythmList T, 00063 *****************************************************************************/ 00064 00065 SetTempoScale(mm(Duration(Quarter), 90)); // set tempo to 90 quarternotes per minute 00066 Print(T); 00067 00068 /***************************************************************************** 00069 prints {(1,6), (1,12), (1,12), (1,12), (1,24), (1,24), (1,6)}. All rhythmic values 00070 are scaled implicitly by Rhythm(). 00071 *****************************************************************************/ 00072 } 00073 00075 /* $Revision: 1.3 $ $Date: 2006/09/05 08:03:08 $ $Author: dgl $ $Name: $ $Id: B0203.cpp,v 1.3 2006/09/05 08:03:08 dgl Exp $ */ 00076 // The Musimat Tutorial © 2006 Gareth Loy 00077 // Derived from Chapter 9 and Appendix B of "Musimathics Vol. 1" © 2006 Gareth Loy 00078 // and published exclusively by The MIT Press. 00079 // This program is released WITHOUT ANY WARRANTY; without even the implied 00080 // warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. 00081 // For information on usage and redistribution, and for a DISCLAIMER OF ALL 00082 // WARRANTIES, see the file, "LICENSE.txt," in this distribution. 00083 // "Musimathics" is available here: http://mitpress.mit.edu/catalog/item/default.asp?ttype=2&tid=10916 00084 // Gareth Loy's Musimathics website: http://www.musimathics.com/ 00085 // The Musimat website: http://www.musimat.com/ 00086 // This program is released under the terms of the GNU General Public License 00087 // available here: http://www.gnu.org/licenses/gpl.txt 00088
1.7.2