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using_20sound_20with_20true_20frequencies
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using_20sound_20with_20true_20frequencies [2018/03/31 13:19] 127.0.0.1 external edit |
using_20sound_20with_20true_20frequencies [2018/04/15 12:48] (current) richardrussell Added syntax highlighting |
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| =====Using SOUND with true frequencies===== | =====Using SOUND with true frequencies===== | ||
| - | //by Richard Russell, May 2014//\\ \\ The [[http://www.bbcbasic.co.uk/bbcwin/manual/bbcwin7.html#sound|SOUND]] statement's third parameter normally specifies the required **pitch** in units of quarter-semitones. For example the value 100 corresponds to **middle C** and the value 136 corresponds to the **A above middle C** (440 Hz, the standard musical pitch).\\ \\ Steps of ¼ semitone will normally be sufficiently fine, even for //glissando// or //vibrato// effects, but occasionally it may be useful to specify the pitch more precisely, in terms of a frequency in **Hertz**. For example if one prefers to use [[http://en.wikipedia.org/wiki/Just_intonation|just intonation]] rather than an equally-tempered scale it would be preferable to approximate the frequencies as accurately as possible (in practice BB4W provides a resolution of approximately one-third Hz).\\ \\ The function **FNfreqout** listed below makes this possible. It takes as a parameter the required frequency in Hz (the maximum being around 10 kHz, but at frequencies that high aliasing effects can be excessive) and returns a value which should be specified as the third parameter of the SOUND statement.\\ \\ Here is an example program illustrating its use:\\ | + | //by Richard Russell, May 2014//\\ \\ The [[http://www.bbcbasic.co.uk/bbcwin/manual/bbcwin7.html#sound|SOUND]] statement's third parameter normally specifies the required **pitch** in units of quarter-semitones. For example the value 100 corresponds to **middle C** and the value 136 corresponds to the **A above middle C** (440 Hz, the standard musical pitch).\\ \\ Steps of ¼ semitone will normally be sufficiently fine, even for //glissando// or //vibrato// effects, but occasionally it may be useful to specify the pitch more precisely, in terms of a frequency in **Hertz**. For example if one prefers to use [[http://en.wikipedia.org/wiki/Just_intonation|just intonation]] rather than an equally-tempered scale it would be preferable to approximate the frequencies as accurately as possible (in practice BB4W provides a resolution of approximately one-third Hz).\\ \\ The function **FNfreqout** listed below makes this possible. It takes as a parameter the required frequency in Hz (the maximum being around 10 kHz, but at frequencies that high aliasing effects can be excessive) and returns a value which should be specified as the third parameter of the SOUND statement.\\ \\ Here is an example program illustrating its use: |
| + | |||
| + | <code bb4w> | ||
| FOR freq = 500 TO 1000 | FOR freq = 500 TO 1000 | ||
| SOUND 1, -15, FNfreqout(freq), 1 | SOUND 1, -15, FNfreqout(freq), 1 | ||
| Line 24: | Line 26: | ||
| ftab%!I% = ftab%!I% AND &FFFF0000 OR INT(f * &10000 / 22050 + 0.5) | ftab%!I% = ftab%!I% AND &FFFF0000 OR INT(f * &10000 / 22050 + 0.5) | ||
| = indx& | = indx& | ||
| + | </code> | ||
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| A limitation of this technique is that a maximum of **255** different frequencies can be 'active' at once. If **FNfreqout** is called more than that number of times the oldest frequencies will be overwritten. If an **ENVELOPE** statement is used it should not contain a pitch component (at least, not unless special measures are taken); amplitude envelopes work as expected.\\ \\ Note that **FNfreqout** works by dynamically rewriting BBC BASIC's frequency table, so if used in a program run from the BB4W **IDE** subsequent programs which use the SOUND statement may be affected. If in doubt quit //BBC BASIC for Windows// and restart it. This issue does not affect its use in a 'compiled' program. | A limitation of this technique is that a maximum of **255** different frequencies can be 'active' at once. If **FNfreqout** is called more than that number of times the oldest frequencies will be overwritten. If an **ENVELOPE** statement is used it should not contain a pitch component (at least, not unless special measures are taken); amplitude envelopes work as expected.\\ \\ Note that **FNfreqout** works by dynamically rewriting BBC BASIC's frequency table, so if used in a program run from the BB4W **IDE** subsequent programs which use the SOUND statement may be affected. If in doubt quit //BBC BASIC for Windows// and restart it. This issue does not affect its use in a 'compiled' program. | ||
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using_20sound_20with_20true_20frequencies.1522502389.txt.gz · Last modified: 2018/03/31 13:19 by 127.0.0.1
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