interpretor/faust-0.9.47mr3/tools/faust2pd/examples/synth/amp.dsp

   1
   2 /* Stereo amplifier stage with bass, treble, gain and balance controls and a
   3    dB meter. */
   4
   5 declare name "amp -- stereo amplifier stage";
   6 declare author "Albert Graef";
   7 declare version "1.0";
   8
   9 import("math.lib");
  10 import("music.lib");
  11
  12 /* Fixed bass and treble frequencies. You might want to tune these for your
  13    setup. */
  14
  15 bass_freq       = 300;
  16 treble_freq     = 1200;
  17
  18 /* Bass and treble gain controls in dB. The range of +/-20 corresponds to a
  19    boost/cut factor of 10. */
  20
  21 bass_gain       = nentry("bass", 0, -20, 20, 0.1);
  22 treble_gain     = nentry("treble", 0, -20, 20, 0.1);
  23
  24 /* Gain and balance controls. */
  25
  26 gain            = db2linear(nentry("gain", 0, -96, 96, 0.1));
  27 bal             = hslider("balance", 0, -1, 1, 0.001);
  28
  29 /* Balance a stereo signal by attenuating the left channel if balance is on
  30    the right and vice versa. I found that a linear control works best here. */
  31
  32 balance         = *(1-max(0,bal)), *(1-max(0,0-bal));
  33
  34 /* Generic biquad filter. */
  35
  36 filter(b0,b1,b2,a0,a1,a2)       = f : (+ ~ g)
  37 with {
  38         f(x)    = (b0/a0)*x+(b1/a0)*x'+(b2/a0)*x'';
  39         g(y)    = 0-(a1/a0)*y-(a2/a0)*y';
  40 };
  41
  42 /* Low and high shelf filters, straight from Robert Bristow-Johnson's "Audio
  43    EQ Cookbook", see http://www.musicdsp.org/files/Audio-EQ-Cookbook.txt. f0
  44    is the shelf midpoint frequency, g the desired gain in dB. S is the shelf
  45    slope parameter, we always set that to 1 here. */
  46
  47 low_shelf(f0,g)         = filter(b0,b1,b2,a0,a1,a2)
  48 with {
  49         S  = 1;
  50         A  = pow(10,g/40);
  51         w0 = 2*PI*f0/SR;
  52         alpha = sin(w0)/2 * sqrt( (A + 1/A)*(1/S - 1) + 2 );
  53
  54         b0 =    A*( (A+1) - (A-1)*cos(w0) + 2*sqrt(A)*alpha );
  55         b1 =  2*A*( (A-1) - (A+1)*cos(w0)                   );
  56         b2 =    A*( (A+1) - (A-1)*cos(w0) - 2*sqrt(A)*alpha );
  57         a0 =        (A+1) + (A-1)*cos(w0) + 2*sqrt(A)*alpha;
  58         a1 =   -2*( (A-1) + (A+1)*cos(w0)                   );
  59         a2 =        (A+1) + (A-1)*cos(w0) - 2*sqrt(A)*alpha;
  60 };
  61
  62 high_shelf(f0,g)        = filter(b0,b1,b2,a0,a1,a2)
  63 with {
  64         S  = 1;
  65         A  = pow(10,g/40);
  66         w0 = 2*PI*f0/SR;
  67         alpha = sin(w0)/2 * sqrt( (A + 1/A)*(1/S - 1) + 2 );
  68
  69         b0 =    A*( (A+1) + (A-1)*cos(w0) + 2*sqrt(A)*alpha );
  70         b1 = -2*A*( (A-1) + (A+1)*cos(w0)                   );
  71         b2 =    A*( (A+1) + (A-1)*cos(w0) - 2*sqrt(A)*alpha );
  72         a0 =        (A+1) - (A-1)*cos(w0) + 2*sqrt(A)*alpha;
  73         a1 =    2*( (A-1) - (A+1)*cos(w0)                   );
  74         a2 =        (A+1) - (A-1)*cos(w0) - 2*sqrt(A)*alpha;
  75 };
  76
  77 /* The tone control. We simply run a low and a high shelf in series here. */
  78
  79 tone            = low_shelf(bass_freq,bass_gain)
  80                 : high_shelf(treble_freq,treble_gain);
  81
  82 /* Envelop follower. This is basically a 1 pole LP with configurable attack/
  83    release time. The result is converted to dB. You have to set the desired
  84    attack/release time in seconds using the t parameter below. */
  85
  86 t               = 0.1;                  // attack/release time in seconds
  87 g               = exp(-1/(SR*t));       // corresponding gain factor
  88
  89 env             = abs : *(1-g) : + ~ *(g) : linear2db;
  90
  91 /* Use this if you want the RMS instead. Note that this doesn't really
  92    calculate an RMS value (you'd need an FIR for that), but in practice our
  93    simple 1 pole IIR filter works just as well. */
  94
  95 rms             = sqr : *(1-g) : + ~ *(g) : sqrt : linear2db;
  96 sqr(x)          = x*x;
  97
  98 /* The dB meters for left and right channel. These are passive controls. */
  99
 100 left_meter(x)   = attach(x, env(x) : hbargraph("left", -96, 10));
 101 right_meter(x)  = attach(x, env(x) : hbargraph("right", -96, 10));
 102
 103 /* The main program. */
 104
 105 process         = hgroup("0-amp", hgroup("1-tone", tone, tone) :
 106                                   hgroup("2-gain", (_*gain, _*gain)))
 107                 : vgroup("3-balance", balance)
 108                 : vgroup("4-meter", (left_meter, right_meter));