Home » Archimedes archive » Acorn User » AU 1998-02 A.adf » PDScheme » ArtToSpr/WavePlayer/Help/TextHelp/4c-Samples
ArtToSpr/WavePlayer/Help/TextHelp/4c-Samples
This website contains an archive of files for the Acorn Electron, BBC Micro, Acorn Archimedes, Commodore 16 and Commodore 64 computers, which Dominic Ford has rescued from his private collection of floppy disks and cassettes.
Some of these files were originally commercial releases in the 1980s and 1990s, but they are now widely available online. I assume that copyright over them is no longer being asserted. If you own the copyright and would like files to be removed, please contact me.
| Tape/disk: | Home » Archimedes archive » Acorn User » AU 1998-02 A.adf » PDScheme |
| Filename: | ArtToSpr/WavePlayer/Help/TextHelp/4c-Samples |
| Read OK: | ✔ |
| File size: | 08A6 bytes |
| Load address: | 0000 |
| Exec address: | 0000 |
File contents
+---------------------------------------------------------------------------+ | WAVE PLAYER | | � 1997, Matthew Wilson | +---------------------------------------------------------------------------+ | SAMPLES | +---------------------------------------------------------------------------+ In order to create sound, your computer must constantly alter the voltage across the sound output, so that your speaker(s) can move. Traditional systems use an analogue system to record the relative voltage, and thus the relative position of the speaker. However, computers cannot store analogue numbers, and thus store a number relating to the voltage. The first important idea is that the speaker has a rest position, and can move both forward and backward from that point. Therefore, the number stored must either have a biased added (ie. unsigned), or be signed. The second idea is that these numbers are discrete; that is to say, they represent the voltage at a particular instant. Therefore, a large number of numbers, or /samples/, are required per second. This is usually referred to as the frequency, or sample rate. CD systems use a rate of 44.1kHz - 44,100 samples per second. However, for most purposes, a rate of nearer 20kHz is adequate. The third idea is that these numbers are integers (whole numbers) and have a maximum and minimum. Therefore, there is a limit to the accuracy to which they can be stored. The causes of the difference between the stored value and the true value is called quantisation. Sound effects are fine stored with 256 values (8 bit), but higher quality requires 12 or 16 bits (4096 and 65536 values respectively). The graphs in the drawfile �4z-graph� show a set of samples taken with relative displacements of -6 to +6. Note the very sharp edges when played back - even if this were possible, then the entire spectrum of frequencies would be produced, creating a �singing� effect. In fact, the sharp edges are impossible to achieve, as the voltage would have to change infinitely quickly.
00000000 2b 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d |+---------------| 00000010 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d |----------------| * 00000040 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2b 0a 7c 20 |------------+.| | 00000050 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 | | 00000060 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 57 | W| 00000070 41 56 45 20 50 4c 41 59 45 52 20 20 20 20 20 20 |AVE PLAYER | 00000080 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 | | 00000090 20 20 20 20 20 20 20 20 20 20 7c 0a 7c 20 20 20 | |.| | 000000a0 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 | | 000000b0 20 20 20 20 20 20 20 a9 20 31 39 39 37 2c 20 4d | . 1997, M| 000000c0 61 74 74 68 65 77 20 57 69 6c 73 6f 6e 20 20 20 |atthew Wilson | 000000d0 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 | | 000000e0 20 20 20 20 20 20 20 20 7c 0a 2b 2d 2d 2d 2d 2d | |.+-----| 000000f0 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d |----------------| * 00000130 2d 2d 2d 2d 2d 2d 2b 0a 7c 20 20 20 20 20 20 20 |------+.| | 00000140 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 | | 00000150 20 20 20 20 20 20 20 20 20 20 20 53 41 4d 50 4c | SAMPL| 00000160 45 53 20 20 20 20 20 20 20 20 20 20 20 20 20 20 |ES | 00000170 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 | | 00000180 20 20 20 20 7c 0a 2b 2d 2d 2d 2d 2d 2d 2d 2d 2d | |.+---------| 00000190 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d |----------------| * 000001d0 2d 2d 2b 0a 0a 20 20 49 6e 20 6f 72 64 65 72 20 |--+.. In order | 000001e0 74 6f 20 63 72 65 61 74 65 20 73 6f 75 6e 64 2c |to create sound,| 000001f0 20 79 6f 75 72 20 63 6f 6d 70 75 74 65 72 20 6d | your computer m| 00000200 75 73 74 20 63 6f 6e 73 74 61 6e 74 6c 79 20 61 |ust constantly a| 00000210 6c 74 65 72 20 74 68 65 20 76 6f 6c 74 61 67 65 |lter the voltage| 00000220 0a 61 63 72 6f 73 73 20 74 68 65 20 73 6f 75 6e |.across the soun| 00000230 64 20 6f 75 74 70 75 74 2c 20 73 6f 20 74 68 61 |d output, so tha| 00000240 74 20 79 6f 75 72 20 73 70 65 61 6b 65 72 28 73 |t your speaker(s| 00000250 29 20 63 61 6e 20 6d 6f 76 65 2e 20 54 72 61 64 |) can move. Trad| 00000260 69 74 69 6f 6e 61 6c 0a 73 79 73 74 65 6d 73 20 |itional.systems | 00000270 75 73 65 20 61 6e 20 61 6e 61 6c 6f 67 75 65 20 |use an analogue | 00000280 73 79 73 74 65 6d 20 74 6f 20 72 65 63 6f 72 64 |system to record| 00000290 20 74 68 65 20 72 65 6c 61 74 69 76 65 20 76 6f | the relative vo| 000002a0 6c 74 61 67 65 2c 20 61 6e 64 20 74 68 75 73 20 |ltage, and thus | 000002b0 74 68 65 0a 72 65 6c 61 74 69 76 65 20 70 6f 73 |the.relative pos| 000002c0 69 74 69 6f 6e 20 6f 66 20 74 68 65 20 73 70 65 |ition of the spe| 000002d0 61 6b 65 72 2e 20 48 6f 77 65 76 65 72 2c 20 63 |aker. However, c| 000002e0 6f 6d 70 75 74 65 72 73 20 63 61 6e 6e 6f 74 20 |omputers cannot | 000002f0 73 74 6f 72 65 20 61 6e 61 6c 6f 67 75 65 0a 6e |store analogue.n| 00000300 75 6d 62 65 72 73 2c 20 61 6e 64 20 74 68 75 73 |umbers, and thus| 00000310 20 73 74 6f 72 65 20 61 20 6e 75 6d 62 65 72 20 | store a number | 00000320 72 65 6c 61 74 69 6e 67 20 74 6f 20 74 68 65 20 |relating to the | 00000330 76 6f 6c 74 61 67 65 2e 0a 0a 20 20 54 68 65 20 |voltage... The | 00000340 66 69 72 73 74 20 69 6d 70 6f 72 74 61 6e 74 20 |first important | 00000350 69 64 65 61 20 69 73 20 74 68 61 74 20 74 68 65 |idea is that the| 00000360 20 73 70 65 61 6b 65 72 20 68 61 73 20 61 20 72 | speaker has a r| 00000370 65 73 74 20 70 6f 73 69 74 69 6f 6e 2c 20 61 6e |est position, an| 00000380 64 20 63 61 6e 0a 6d 6f 76 65 20 62 6f 74 68 20 |d can.move both | 00000390 66 6f 72 77 61 72 64 20 61 6e 64 20 62 61 63 6b |forward and back| 000003a0 77 61 72 64 20 66 72 6f 6d 20 74 68 61 74 20 70 |ward from that p| 000003b0 6f 69 6e 74 2e 20 54 68 65 72 65 66 6f 72 65 2c |oint. Therefore,| 000003c0 20 74 68 65 20 6e 75 6d 62 65 72 20 73 74 6f 72 | the number stor| 000003d0 65 64 0a 6d 75 73 74 20 65 69 74 68 65 72 20 68 |ed.must either h| 000003e0 61 76 65 20 61 20 62 69 61 73 65 64 20 61 64 64 |ave a biased add| 000003f0 65 64 20 28 69 65 2e 20 75 6e 73 69 67 6e 65 64 |ed (ie. unsigned| 00000400 29 2c 20 6f 72 20 62 65 20 73 69 67 6e 65 64 2e |), or be signed.| 00000410 0a 0a 20 20 54 68 65 20 73 65 63 6f 6e 64 20 69 |.. The second i| 00000420 64 65 61 20 69 73 20 74 68 61 74 20 74 68 65 73 |dea is that thes| 00000430 65 20 6e 75 6d 62 65 72 73 20 61 72 65 20 64 69 |e numbers are di| 00000440 73 63 72 65 74 65 3b 20 74 68 61 74 20 69 73 20 |screte; that is | 00000450 74 6f 20 73 61 79 2c 20 74 68 65 79 0a 72 65 70 |to say, they.rep| 00000460 72 65 73 65 6e 74 20 74 68 65 20 76 6f 6c 74 61 |resent the volta| 00000470 67 65 20 61 74 20 61 20 70 61 72 74 69 63 75 6c |ge at a particul| 00000480 61 72 20 69 6e 73 74 61 6e 74 2e 20 54 68 65 72 |ar instant. Ther| 00000490 65 66 6f 72 65 2c 20 61 20 6c 61 72 67 65 20 6e |efore, a large n| 000004a0 75 6d 62 65 72 20 6f 66 0a 6e 75 6d 62 65 72 73 |umber of.numbers| 000004b0 2c 20 6f 72 20 2f 73 61 6d 70 6c 65 73 2f 2c 20 |, or /samples/, | 000004c0 61 72 65 20 72 65 71 75 69 72 65 64 20 70 65 72 |are required per| 000004d0 20 73 65 63 6f 6e 64 2e 20 54 68 69 73 20 69 73 | second. This is| 000004e0 20 75 73 75 61 6c 6c 79 20 72 65 66 65 72 72 65 | usually referre| 000004f0 64 20 74 6f 0a 61 73 20 74 68 65 20 66 72 65 71 |d to.as the freq| 00000500 75 65 6e 63 79 2c 20 6f 72 20 73 61 6d 70 6c 65 |uency, or sample| 00000510 20 72 61 74 65 2e 20 43 44 20 73 79 73 74 65 6d | rate. CD system| 00000520 73 20 75 73 65 20 61 20 72 61 74 65 20 6f 66 20 |s use a rate of | 00000530 34 34 2e 31 6b 48 7a 20 2d 20 34 34 2c 31 30 30 |44.1kHz - 44,100| 00000540 0a 73 61 6d 70 6c 65 73 20 70 65 72 20 73 65 63 |.samples per sec| 00000550 6f 6e 64 2e 20 48 6f 77 65 76 65 72 2c 20 66 6f |ond. However, fo| 00000560 72 20 6d 6f 73 74 20 70 75 72 70 6f 73 65 73 2c |r most purposes,| 00000570 20 61 20 72 61 74 65 20 6f 66 20 6e 65 61 72 65 | a rate of neare| 00000580 72 20 32 30 6b 48 7a 20 69 73 0a 61 64 65 71 75 |r 20kHz is.adequ| 00000590 61 74 65 2e 0a 0a 20 20 54 68 65 20 74 68 69 72 |ate... The thir| 000005a0 64 20 69 64 65 61 20 69 73 20 74 68 61 74 20 74 |d idea is that t| 000005b0 68 65 73 65 20 6e 75 6d 62 65 72 73 20 61 72 65 |hese numbers are| 000005c0 20 69 6e 74 65 67 65 72 73 20 28 77 68 6f 6c 65 | integers (whole| 000005d0 20 6e 75 6d 62 65 72 73 29 20 61 6e 64 20 68 61 | numbers) and ha| 000005e0 76 65 0a 61 20 6d 61 78 69 6d 75 6d 20 61 6e 64 |ve.a maximum and| 000005f0 20 6d 69 6e 69 6d 75 6d 2e 20 54 68 65 72 65 66 | minimum. Theref| 00000600 6f 72 65 2c 20 74 68 65 72 65 20 69 73 20 61 20 |ore, there is a | 00000610 6c 69 6d 69 74 20 74 6f 20 74 68 65 20 61 63 63 |limit to the acc| 00000620 75 72 61 63 79 20 74 6f 20 77 68 69 63 68 0a 74 |uracy to which.t| 00000630 68 65 79 20 63 61 6e 20 62 65 20 73 74 6f 72 65 |hey can be store| 00000640 64 2e 20 54 68 65 20 63 61 75 73 65 73 20 6f 66 |d. The causes of| 00000650 20 74 68 65 20 64 69 66 66 65 72 65 6e 63 65 20 | the difference | 00000660 62 65 74 77 65 65 6e 20 74 68 65 20 73 74 6f 72 |between the stor| 00000670 65 64 20 76 61 6c 75 65 20 61 6e 64 0a 74 68 65 |ed value and.the| 00000680 20 74 72 75 65 20 76 61 6c 75 65 20 69 73 20 63 | true value is c| 00000690 61 6c 6c 65 64 20 71 75 61 6e 74 69 73 61 74 69 |alled quantisati| 000006a0 6f 6e 2e 20 53 6f 75 6e 64 20 65 66 66 65 63 74 |on. Sound effect| 000006b0 73 20 61 72 65 20 66 69 6e 65 20 73 74 6f 72 65 |s are fine store| 000006c0 64 20 77 69 74 68 20 32 35 36 0a 76 61 6c 75 65 |d with 256.value| 000006d0 73 20 28 38 20 62 69 74 29 2c 20 62 75 74 20 68 |s (8 bit), but h| 000006e0 69 67 68 65 72 20 71 75 61 6c 69 74 79 20 72 65 |igher quality re| 000006f0 71 75 69 72 65 73 20 31 32 20 6f 72 20 31 36 20 |quires 12 or 16 | 00000700 62 69 74 73 20 28 34 30 39 36 20 61 6e 64 20 36 |bits (4096 and 6| 00000710 35 35 33 36 0a 76 61 6c 75 65 73 20 72 65 73 70 |5536.values resp| 00000720 65 63 74 69 76 65 6c 79 29 2e 0a 0a 20 20 54 68 |ectively)... Th| 00000730 65 20 67 72 61 70 68 73 20 69 6e 20 74 68 65 20 |e graphs in the | 00000740 64 72 61 77 66 69 6c 65 20 90 34 7a 2d 67 72 61 |drawfile .4z-gra| 00000750 70 68 91 20 73 68 6f 77 20 61 20 73 65 74 20 6f |ph. show a set o| 00000760 66 20 73 61 6d 70 6c 65 73 20 74 61 6b 65 6e 20 |f samples taken | 00000770 77 69 74 68 0a 72 65 6c 61 74 69 76 65 20 64 69 |with.relative di| 00000780 73 70 6c 61 63 65 6d 65 6e 74 73 20 6f 66 20 2d |splacements of -| 00000790 36 20 74 6f 20 2b 36 2e 20 4e 6f 74 65 20 74 68 |6 to +6. Note th| 000007a0 65 20 76 65 72 79 20 73 68 61 72 70 20 65 64 67 |e very sharp edg| 000007b0 65 73 20 77 68 65 6e 20 70 6c 61 79 65 64 0a 62 |es when played.b| 000007c0 61 63 6b 20 2d 20 65 76 65 6e 20 69 66 20 74 68 |ack - even if th| 000007d0 69 73 20 77 65 72 65 20 70 6f 73 73 69 62 6c 65 |is were possible| 000007e0 2c 20 74 68 65 6e 20 74 68 65 20 65 6e 74 69 72 |, then the entir| 000007f0 65 20 73 70 65 63 74 72 75 6d 20 6f 66 20 66 72 |e spectrum of fr| 00000800 65 71 75 65 6e 63 69 65 73 0a 77 6f 75 6c 64 20 |equencies.would | 00000810 62 65 20 70 72 6f 64 75 63 65 64 2c 20 63 72 65 |be produced, cre| 00000820 61 74 69 6e 67 20 61 20 90 73 69 6e 67 69 6e 67 |ating a .singing| 00000830 91 20 65 66 66 65 63 74 2e 20 49 6e 20 66 61 63 |. effect. In fac| 00000840 74 2c 20 74 68 65 20 73 68 61 72 70 20 65 64 67 |t, the sharp edg| 00000850 65 73 20 61 72 65 0a 69 6d 70 6f 73 73 69 62 6c |es are.impossibl| 00000860 65 20 74 6f 20 61 63 68 69 65 76 65 2c 20 61 73 |e to achieve, as| 00000870 20 74 68 65 20 76 6f 6c 74 61 67 65 20 77 6f 75 | the voltage wou| 00000880 6c 64 20 68 61 76 65 20 74 6f 20 63 68 61 6e 67 |ld have to chang| 00000890 65 20 69 6e 66 69 6e 69 74 65 6c 79 0a 71 75 69 |e infinitely.qui| 000008a0 63 6b 6c 79 2e 0a |ckly..| 000008a6
.