Atari 2600 VCS Sound Frequency and Waveform Guide
From 8BitDev.org - Atari 7800 Development Wiki
Subject: [stella] Frequency and Waveform Guide
From: Eckhard_Stolberg@xxxxxxxxxxxxxxxxxxxxx (Eckhard Stolberg)
Date: Sun, 22 Jun 1997 16:16:32 +0200
ATARI 2600 VCS SOUND FREQUENCY AND WAVEFORM GUIDE
by Eckhard Stolberg
last modified on 22.6.97 (first version)
==============================================================================
These tables have been calculated with the information found in Ron Fries'
TIASOUND emulation package. I have done some sampling on my own to verify
it and got basically what Ron's theory suggested. Also I have compared my
results with Glenn Saunders's note tables and found them to be almost the
same.
However, I might have missed something important or simply miscalculated
some of the values. Therefore it would be nice, if someone could do some
sampling or recalculating to verify or correct these tables.
The cent values have been calculated with rounded frequencies. Therefore
they are not as acurate as they might look, especially the ones for the
lower frequencies.
==============================================================================
The Atari 2600 VCS produces it's sound with some shift registers of various
lengths. The speed at which it shifts the registers can be set to either the
pixelclock/114 or to the CPUclock/114, which means two shifts per scanline
or a third of this. Since a NTSC VCS produces 262 scanlines per frame and 60
frames per second this results in output rates of 31440 Hz and 10480 Hz.
PAL TVs produce only 312 scanlines and 50 frames, so the output rates are
only 31200 Hz and 10400 Hz.
A pitch value of n stored in the AUDFx registers modifies the frequency in a
way, that n possibilities to shift are left out.
The distortion values stored in the AUDCx registers select the clock to use.
They also select two shift registers of various lengths. One of these is the
source pattern. Every time a 1 is shifted out of the source pattern, the
output is set high. If a 0 is shifted out, the output is set low.
The other shift register is a clock modifier. Every time a 1 is shifted out,
the effect of the source pattern can take place. If a 0 is shiftet out, the
bit, that is shifted out of the source pattern, has no effect on the output.
Since the source pattern and the clock modifier registers match up perfectly
except for distortion 2 & 3, my tables only list the resulting output
bitstream.
More information on the patterns can be found in the documentation for Ron
Fries' TIASOUND emulation package.
However, since the output switches so fast between high and low, the resulting
waveforms are not perfect squarewaves. For example distortion 4 with a pitch
value of 0 would flip the output at a rate of 15720 Hz. This is so fast,
that the membrane of the speaker couldn't swing very far before it has to
change it's direction. Therefore no audible sound is produced.
==============================================================================
How to read the tables:
DISTORTION is the value to be stored in the AUDCx registers.
WAVEFORM: A 1 means the output is set high, a 0 means the output is set low.
For distortion 2 & 3 it is source pattern -> clock modifier pattern.
CLOCKSPEED is the speed at which the registers are shifted.
PITCH is the value to be stored in the AUDFx registers.
NTSC & PAL are the calculated frequencies for the specified TV norm.
NOTE is the note value, that is closest to the calculated frequency.
FREQ is the frequency that this note would have if A4=440 Hz.
CENT specifies how many percent the calculated frequency is off it's
corresponding note frequency
Lines marked as below have such a low frequency, that it really doesn't
matter if it is C or C# rumble.
==============================================================================
Distortion: 0 & 11
Waveform : always high
(used to output 4-bit samples by changing the volume very fast)
Clockspeed: pixelclock/114
Distortion: 1
Waveform : 001010000111011
Clockspeed: pixelclock/114
Pitch NTSC Note Freq Cent PAL Note Freq Cent
----- ---- ---- ---- ---- --- ---- ---- ----
0 2096 c7 2093 +2 2080 c7 2093 -1
1 1048 c6 1046.5 +2 1040 c6 1046.5 -1
2 698.7 f5 698.5 0 693.3 f5 698.5 -1
3 524 c5 523.3 +2 520 c5 523.3 -1
4 419.2 g#4 415.3 +16 416 g#4 415.3 +3
5 349.3 f4 349.2 0 346.7 f4 349.2 -13
6 299.4 d4 293.7 +33 297.1 d4 293.7 +20
7 262 c4 261.6 +3 260 c4 261.6 -11
8 232.9 a#3 233.1 -2 231.1 a#3 233.1 -15
9 209.6 g#3 207.7 +15 208 g#3 207.7 +2
10 190.5 f#3 185 +50 189.1 f#3 185 +37
11 174.7 f3 174.6 +1 173.3 f3 174.6 -13
12 161.2 e3 164.8 -39 160 d#3 155.6 +48
13 149.7 d3 146.8 +33 148.6 d3 146.8 +20
14 139.7 c#3 138.6 +13 138.7 c#3 138.6 +1
15 131 c3 130.8 +3 130 c3 130.8 -11
16 123.3 h2 123.5 -3 122.4 h2 123.5 -16
17 116.4 a#2 116.4 0 115.6 a#2 116.5 -14
18 110.3 a2 110 +5 109.5 a2 110 -8
19 104.8 g#2 103.8 +16 104 g#2 103.8 +3
20 99.8 g2 98 +31 99 g2 98 +17
21 95.3 g2 98 -49 94.5 f#2 92.5 +36
22 91.1 f#2 92.5 -27 90.4 f#2 92.5 -40
23 87.3 f2 87.3 0 86.7 f2 87.3 -12
24 83.8 e2 82.4 +29 83.2 e2 82.4 +16
25 80.6 e2 82.4 -39 80 d#2 77.8 +48
26 77.6 d#2 77.8 -5 77 d#2 77.8 -18
27 74.9 d2 73.4 +34 74.3 d2 73.4 +20
28 72.3 d2 73.4 -27 71.7 d2 73.4 -41
29 69.9 c#2 69.3 +15 69.3 c#2 69.3 0
30 67.6 c#2 69.3 -44 67.1 c2 65.4 +44
31 65.5 c2 65.4 +3 65 c2 65.4 -11
Distortion: 2 & 3
Waveform : 001010000111011->0100000000000000000100000000000 (465 bits long)
001010000111011->0010110011111000110111010100001 (465 bits long)
Clockspeed: pixelclock/114
Pitch NTSC Note Freq Cent PAL Note Freq Cent
----- ---- ---- ---- ---- --- ---- ---- ----
0 67.6 c#2 69.3 -44 67.1 c2 65.4 +44
1 33.8 c#1 34.6 -42 33.5 c1 32.7 +42
2 22.5 f#0 23.1 -46 22.4 f0 21.8 +46
3 16.9 c#0 17.3 -44 16.8 c0 16.4 +44
4 13.5 below 13.4 below
5 11.3 11.2
6 9.7 9.6
7 8.5 8.4
8 7.5 7.5
9 6.8 6.7
10 6.1 6.1
11 5.6 5.6
12 5.2 5.2
13 4.8 4.8
14 4.5 4.5
15 4.2 4.2
16 4 4
17 3.8 3.7
18 3.6 3.5
19 3.4 3.4
20 3.2 3.2
21 3.1 3
22 3 2.9
23 2.8 2.8
24 2.7 2.7
25 2.6 2.6
26 2.5 2.5
27 2.4 2.4
28 2.3 2.3
29 2.3 2.2
30 2.2 2.2
31 2.1 2.1
Distortion: 4 & 5
Waveform : 01
Clockspeed: pixelclock/114
Pitch NTSC Note Freq Cent PAL Note Freq Cent
----- ---- ---- ---- ---- --- ---- ---- ----
0 15720 silent 15600 silent
1 7860 h8 7902.1 -9 7800 h8 7902.1 -23
2 5240 e8 5274 -11 5200 e8 5274 -25
3 3930 h7 3951.1 -10 3900 h7 3951.1 -23
4 3144 g7 3136 +4 3120 g7 3136 -9
5 2620 e7 2637 -11 2600 e7 2637 -25
6 2245.7 c#7 2217.5 +21 2228.6 c#7 2217.5 +8
7 1965 h6 1975.5 -9 1950 h6 1975.5 -23
8 1746.7 a6 1760 -13 1733.3 a6 1760 -27
9 1572 g6 1568 +4 1560 g6 1568 -9
10 1429.1 f6 1396.9 +39 1418.2 f6 1396.9 +25
11 1310 e6 1318.5 -11 1300 e6 1318.5 -25
12 1209.2 d6 1174.7 +49 1200 d6 1174.7 +36
13 1122.9 c#6 1108.7 +22 1114.3 c#6 1108.7 +8
14 1048 c6 1046.5 +2 1040 c6 1046.5 -11
15 982.5 h5 987.8 -10 975 h5 987.8 -23
16 924.7 a#5 932.3 -15 917.6 a#5 932.3 -28
17 873.3 a5 880 -14 866.7 a5 880 -27
18 827.4 g#5 830.6 -7 821.1 g#5 830.6 -20
19 786 g5 784 +4 780 g5 784 -9
20 748.6 f#5 740 +20 742.9 f#5 740 +7
21 714.5 f5 698.5 +39 709.1 f5 698.5 +26
22 683.5 f5 698.5 -38 678.3 e5 659.5 +48
23 655 e5 659.3 -12 650 e5 659.3 -25
24 628.8 d#5 622.3 +18 624 d#5 622.3 +5
25 604.6 d5 587.3 +49 600 d5 587.3 +36
26 582.2 d5 587.3 -16 577.8 d5 587.3 -29
27 561.4 c#5 554.4 +21 557.1 c#5 554.4 +8
28 542.1 c#5 554.4 -40 537.9 c5 523.3 +47
29 524 c5 523.3 +2 520 c5 523.3 -11
30 507.1 h4 493.9 +45 503.2 h4 493.9 +32
31 491.3 h4 493.9 -9 487.5 h4 493.9 -23
Distortion: 7 & 9 6 & 10
Waveform : 0010110011111000110111010100001 1111111111111000000000000000000
Clockspeed: pixelclock/114
Pitch NTSC Note Freq Cent PAL Note Freq Cent
----- ---- ---- ---- ---- --- ---- ---- ----
0 1014.2 h5 987.8 +45 1006.5 h5 987.8 +32
1 507.1 h4 493.9 +45 503.2 h4 493.9 +32
2 338.1 e4 329.6 +43 335.5 e4 329.6 +30
3 253.5 h3 246.9 +45 251.6 h3 246.9 +32
4 202.8 g#3 207.7 -42 201.3 g3 196 +45
5 169 e3 164.8 +43 167.7 e3 164.8 +30
6 144.9 d3 146.8 -23 143.8 d3 146.8 -37
7 126.8 h2 123.5 +42 125.8 h2 123.5 +32
8 112.7 a2 110 +42 111.8 a2 110 +28
9 101.4 g#2 103.8 -41 100.6 g2 98 +45
10 92.2 f#2 92.5 -6 91.5 f#2 92.5 -19
11 84.5 e2 82.4 +43 83.9 e2 82.4 +31
12 78 d#2 77.8 +4 77.4 d#2 77.8 -9
13 72.4 d2 73.4 -24 71.9 d2 73.4 -37
14 67.6 c#2 69.3 -44 67.1 c2 65.4 +44
15 63.4 h1 61.7 +46 62.9 h1 61.7 +32
16 59.7 a#1 58.3 +41 59.2 a#1 58.3 +26
17 56.3 a1 55 +39 55.9 a1 55 +27
18 53.4 g#1 51.9 +48 53 g#1 51.9 +35
19 50.7 g#1 51.9 -41 50.3 g1 49 +45
20 48.3 g1 49 -25 47.9 g1 49 -39
21 46.1 f#1 46.2 -4 45.7 f#1 46.2 -20
22 44.1 f1 43.7 +16 43.8 f1 43.7 +4
23 42.3 e1 41.2 +44 41.9 e1 41.2 +28
24 40.6 e1 41.2 -26 40.3 e1 41.2 -39
25 39 d#1 38.9 +4 38.7 d#1 38.9 -9
26 37.6 d1 36.7 +41 37.3 d1 36.7 +27
27 36.2 d1 36.7 -24 35.9 d1 36.7 -38
28 35 c#1 34.6 +19 34.7 c#1 34.6 +5
29 33.8 c#1 34.6 -42 33.5 c1 32.7 +42
30 32.7 c1 32.7 0 32.5 c1 32.7 -11
31 31.7 h0 30.9 +44 31.5 h0 30.9 +33
Distortion: 8
Waveform : 511 bits long (white noise)
Clockspeed: pixelclock/114
Pitch NTSC Note Freq Cent PAL Note Freq Cent
----- ---- ---- ---- ---- --- ---- ---- ----
0 61.5 h1 61.7 -6 61.1 h1 61.7 -18
1 30.8 h0 30.9 -6 30.5 h0 30.9 -22
2 20.5 e0 20.6 -8 20.4 e0 20.6 -17
3 15.4 below 15.3 below
4 12.3 12.2
5 10.3 10.2
6 8.8 8.7
7 7.7 7.6
8 6.8 6.8
9 6.2 6.1
10 5.6 5.6
11 5.1 5.1
12 4.7 4.7
13 4.4 4.4
14 4.1 4.1
15 3.8 3.8
16 3.6 3.6
17 3.4 3.4
18 3.2 3.2
19 3.1 3.1
20 2.9 2.9
21 2.8 2.8
22 2.7 2.7
23 2.6 2.5
24 2.5 2.4
25 2.4 2.3
26 2.3 2.3
27 2.2 2.2
28 2.1 2.1
29 2 2
30 2 2
31 1.9 1.9
Distortion: 12 & 13
Waveform : 10
Clockspeed: CPUclock/114
Pitch NTSC Note Freq Cent PAL Note Freq Cent
----- ---- ---- ---- ---- --- ---- ---- ----
0 5240 e8 5274 -11 5200 e8 5274 -25
1 2620 e7 2637 -11 2600 e7 2637 -25
2 1746.6 a6 1760 -14 1733.3 a6 1760 -27
3 1310 e6 1318.5 -11 1300 e6 1318.5 -25
4 1048 c6 1046.5 +2 1040 c6 1046.5 -11
5 873.3 a5 880 -14 866.7 a5 880 -27
6 748.6 f#5 740 +20 742.9 f#5 740 +7
7 655 e5 659.3 -12 650 e5 659.3 -25
8 582.2 d5 587.3 -16 577.8 d5 587.3 -29
9 524 c5 523.3 +2 520 c5 523.3 -11
10 476.4 a#4 466.2 +39 472.7 a#4 466.2 +23
11 436.7 a4 440 -13 433.3 a4 440 -27
12 403.1 g4 392 +48 400 g4 392 +34
13 374.3 f#4 370 +20 371.4 f#4 370 +6
14 349.3 f4 349.2 0 346.7 f4 349.2 -13
15 327.5 e4 329.6 -11 325 e4 329.6 -25
16 308.2 d#4 311.1 -17 305.9 d#4 311.1 -30
17 291.1 d4 293.7 -16 288.9 d4 293.7 -29
18 275.8 c#4 277.2 -9 273.7 c#4 277.2 -22
19 262 c4 261.6 +3 260 c4 261.6 -11
20 249.5 h3 246.9 +18 247.6 h3 246.9 +5
21 238.2 a#3 233.1 +37 236.4 a#3 233.1 +24
22 227.8 a#3 233.1 -40 226.1 a3 220 +47
23 218.3 a3 220 -14 216.7 a3 220 -27
24 209.6 g#3 207.7 +15 208 g#3 207.7 +2
25 201.5 g3 196 +47 200 g3 196 +34
26 194.1 g3 196 -17 192.6 g3 196 -31
27 187.1 f#3 185 +19 185.7 f#3 185 +6
28 180.7 f#3 185 -41 179.3 f3 174.6 +45
29 174.7 f3 174.6 +1 173.3 f3 174.6 -13
30 169 e3 164.8 +43 167.7 e3 164.8 +30
31 163.8 e3 164.8 -11 162.5 e3 164.8 -25
Distortion: 14 15
Waveform : 1111111111111000000000000000000 0010110011111000110111010100001
Clockspeed: CPUclock/114
Pitch NTSC Note Freq Cent PAL Note Freq Cent
----- ---- ---- ---- ---- --- ---- ---- ----
0 338.1 e4 329.6 +43 335.5 e4 329.6 +30
1 169 e3 164.8 +43 167.7 e3 164.8 +30
2 112.7 a2 110 +42 111.8 a2 110 +28
3 84.5 e2 82.4 +43 83.9 e2 82.4 +31
4 67.6 c#2 69.3 -44 67.1 c2 65.4 +44
5 56.3 a1 55 +39 55.9 a1 55 +27
6 48.3 g1 49 -25 47.9 g1 49 -39
7 42.3 e1 41.2 +44 41.9 e1 41.2 +28
8 37.6 d1 36.7 +41 37.3 d1 36.7 +27
9 33.8 c#1 34.6 -42 33.5 c1 32.7 +42
10 30.7 h0 30.9 -11 30.5 h0 30.9 -22
11 28.2 a0 27.5 +44 28 a0 27.5 +31
12 26 g#0 26 0 25.8 g#0 26 -13
13 24.1 g0 24.5 -29 24 g0 24.5 -36
14 22.5 f#0 23.1 -46 22.4 f0 21.8 +46
15 21.1 e0 20.6 +42 21 e0 20.6 +33
16 19.9 d#0 19.4 +42 19.7 d#0 19.4 +25
17 18.8 d0 18.4 +40 18.6 d0 18.4 +20
18 17.8 c#0 17.3 +45 17.7 c#0 17.3 +36
19 16.9 c#0 17.3 -44 16.8 c0 16.4 +44
20 16.1 c0 16.4 -30 16 c0 16.4 -40
21 15.4 below 15.2 below
22 14.7 14.6
23 14.1 14
24 13.5 13.4
25 13 12.9
26 12.5 12.4
27 12.1 12
28 11.7 11.6
29 11.3 11.2
30 10.9 10.8
31 10.6 10.5
