1 /*---------------------------------------------------------------------------*
2   Project:  SP objects and LPF coefficients for axfilter demo
3   File:     lpfdemo.h
4 
5   Copyright (C)1998-2006 Nintendo  All Rights Reserved.
6 
7   These coded instructions, statements, and computer programs contain
8   proprietary information of Nintendo of America Inc. and/or Nintendo
9   Company Ltd., and are protected by Federal copyright law.  They may
10   not be disclosed to third parties or copied or duplicated in any form,
11   in whole or in part, without the prior written consent of Nintendo.
12 
13   $Log: lpfdemo.h,v $
14   Revision 1.2  02/02/2006 02:36:39  aka
15   Added copyright.
16 
17   $NoKeywords: $
18 
19  *---------------------------------------------------------------------------*/
20 
21 // -----------------------------------------------------------------
22 // SP table entry indices for lpfdemo.spd
23 // -----------------------------------------------------------------
24 
25 #define MSX_GS_LEFT         0
26 #define MSX_GS_RIGHT        1
27 #define MSX_SPL_LEFT        2
28 #define MSX_SPL_RIGHT       3
29 #define MSX_CAR_LEFT        4
30 #define MSX_CAR_RIGHT       5
31 #define SFX_GUNSHOT         6
32 #define SFX_PINK            7
33 #define SFX_WHITE           8
34 #define SFX_MACHINE_GUN     9
35 #define SFX_EXPLOSION       10
36 #define SFX_FOOTSTEPS       11
37 #define SFX_NGC_MAN         12
38 
39 // -----------------------------------------------------------------
40 // Coefficient table for LPF
41 // -----------------------------------------------------------------
42 // The filter is a simple one-pole function:
43 //
44 //     y(n) = a0*x(n) - b0*y(n-1)
45 //
46 // Where x(n) is the current input sample, and y(n-1) is the previous
47 // output sample. The coefficients a0 and b0 can be calculated thusly:
48 //
49 //     c  = 2.0 - cos(2*pi * freq)
50 //     b0 = sqrt(c^2 - 1) - c
51 //     a0 = 1 + b0
52 //
53 // Where freq is in HZ and must be within the range:
54 //
55 //     0 > freq < 16,000
56 //
57 // The coefficients must be unsigned, 16-bit words in fixed-point
58 // format, having 1 bit of integer and 15 bits of fraction.
59 // Furthermore, the b0 term must be (arithmetically) negated before
60 // being sent to the DSP. This is because of an optimization in the
61 // DSP filter calculation that is afforded by the absence of a sign
62 // bit in the coefficients.
63 //
64 
65 #define NUM_FREQ_CUTOFF 24  // we're using 24 steps in the freq range
66 
67 typedef struct
68 {
69     u16 a0;
70     u16 b0;
71     char *text;
72 
73 } __LPF_COEF;
74 
75 static __LPF_COEF __coefs[] =
76 {
77     {  0x6a09, 0x15f6, "16000 Hz" },
78     {  0x6871, 0x178e, "12800 Hz" },
79     {  0x6463, 0x1b9c, "10240 Hz" },
80     {  0x5db3, 0x224c, "8000 Hz " },
81     {  0x5618, 0x29e7, "6400 Hz " },
82     {  0x4d7a, 0x3285, "5120 Hz " },
83     {  0x4367, 0x3c98, "4000 Hz " },
84     {  0x3a5a, 0x45a5, "3200 Hz " },
85     {  0x31c5, 0x4e3a, "2560 Hz " },
86     {  0x2924, 0x56db, "2000 Hz " },
87     {  0x2244, 0x5dbb, "1600 Hz " },
88     {  0x1c50, 0x63af, "1280 Hz " },
89     {  0x16c0, 0x693f, "1000 Hz " },
90     {  0x1292, 0x6d6d, "800 Hz  " },
91     {  0x0f18, 0x70e7, "640 Hz  " },
92     {  0x0bf5, 0x740a, "500 Hz  " },
93     {  0x09a9, 0x7656, "400 Hz  " },
94     {  0x07ca, 0x7835, "320 Hz  " },
95     {  0x0646, 0x79b9, "256 Hz  " },
96     {  0x04ed, 0x7b12, "200 Hz  " },
97     {  0x03f5, 0x7c0a, "160 Hz  " },
98     {  0x032d, 0x7cd2, "128 Hz  " },
99     {  0x027d, 0x7d82, "100 Hz  " },
100     {  0x01fe, 0x7e01, "80 Hz   " }
101 };
102