I'm currently working at the component level on the driver circuit (full-wave rectifier with RC element) – specifically, simulating diodes, capacitors, and resistors. My goal is to finally replace the dummy circuit in VU Meter 2 so it behaves as intended.

What do you think – does it make sense (apart from response and RC time constants) to offer component parameters for adjustment?
Things like settings for forward voltage, diode knee, leakage, tolerances, DC filter, etc.?

This would give users who are interested the ability to essentially "swap out" diodes and capacitors, allowing them to get even closer to emulating their own analog VU meter. It would allow for the simulation of VU Meters from high-end to low-grade... Too much? Or Cool?

Please, let me know!

Here are the measurements with my set default settings:


View attachment 58115

 

Last edited: Jun 28, 2025 at 12:03 AM

Is it possible port to VST3??

 

Cool

 

Plugin is in alpha phase. When VU Meter 2 has successfully passed the beta phase, then potentially yes.

Anyone here fluent in C++ or Rust?

 

The Rectifier/RC-Simulation is done. If you want to play around with it as a single component, here it is:

Code:

desc:Rectifier/RC-Simulation (ZenoMOD)
author:   ZenoMOD
released: 2025
version:  1.00

A detailed rectifier and RC-filter simulation.

//////// CREDITS ////////
ADAA implementations are based on the methods described in:
Parker et al (2016), DAFx-16, "Reducing the Aliasing of Nonlinear Waveshaping Using Continuous-Time Convolution".
Bilbao et al (2017), IEEE, "Antiderivative Antialiasing for Memoryless Nonlinearities".

slider1:dc_filter=1<0,1,1{Off,On}>Input DC Filter
slider10:charge_ms=0.22<0.01,2,0.01>Response Time (ms)
slider11:discharge_ms=350<150,1500,5>RC Time Constant (ms)
slider20:diode_db=-80<-100,-60,1>Forward Voltage (dB)
slider21:diode_knee_db=6<0.1,12,0.1>Diode Knee (dB)
slider30:leakage_pct=0.05<0.01,5,0.001>Leakage Current (%)
slider31:tolerance_pct=5<0,20,0.1>Aging-Tolerance (%)
slider40:noise_onoff=1<0,1,1{Off,On}>Noise
slider41:noise_db=-98<-120,-60,1>Electronic Noise (dB)
slider51:rect_adaa_mode=0<0,2,1{Off,ADAA 1,ADAA 2}>Rectifier Anti-Aliasing
slider52:follower_adaa_mode=1<0,2,1{Off,ADAA 1,ADAA 2}>Follower Anti-Aliasing
slider60:monitor_output=0<0,1,1{Off,On}>Monitor Output?


options:no_meter

@init
  epsilon = 0.000000000001;

  function lin_to_db(lin) ( 6 * log(max(epsilon, abs(lin))) / log(2) );
  function db_to_lin(db) ( 2^(db / 6) );
  function ms_to_coeff(ms) ( exp(-1 / (max(epsilon, ms) * 0.001 * srate)) );
  function tanh(x) (
    abs(x) > 20 ? (
      x > 0 ? 1 : -1
    ) : (
      (em2ax = exp(-2*abs(x))) >= 0 ? (
        (1-em2ax) / (1+em2ax) * (x >= 0 ? 1 : -1)
      ) : (
        x > 0 ? 1 : -1
      )
    )
  );
 
  function leakage_to_coeff(pct_s) ( pow(max(0.01, 1 - pct_s / 100), 1 / srate) );


  function F1_abs(val) ( 0.5 * val * abs(val) );
  function F2_abs(val) ( (1/6) * val * val * abs(val) );
 
  function adaa_abs(in_val)
    instance(prev_s1, prev_s2)
    local(out_val, dx, dx1, dx2, d_sum, term1, term2)
  (
    rect_adaa_mode == 0 ? (
      out_val = abs(in_val);
    ) :
    rect_adaa_mode == 1 ? (
      dx = in_val - prev_s1;
      out_val = (abs(dx) < epsilon) ? abs((in_val + prev_s1) * 0.5) : (F1_abs(in_val) - F1_abs(prev_s1)) / dx;
    ) : (
      dx1 = in_val - prev_s1;
      term1 = (abs(dx1) < epsilon) ? F1_abs((in_val + prev_s1) * 0.5) : (F2_abs(in_val) - F2_abs(prev_s1)) / dx1;
      dx2 = prev_s1 - prev_s2;
      term2 = (abs(dx2) < epsilon) ? F1_abs((prev_s1 + prev_s2) * 0.5) : (F2_abs(prev_s1) - F2_abs(prev_s2)) / dx2;
      d_sum = in_val - prev_s2;
      out_val = (abs(d_sum) < epsilon) ? ( (abs(dx_fallback=prev_s1-prev_s2) < epsilon) ? abs((prev_s1+prev_s2)*0.5) : (F1_abs(prev_s1)-F1_abs(prev_s2))/dx_fallback ) : ( 2 * (term1 - term2) / d_sum );
    );
    prev_s2 = prev_s1;
    prev_s1 = in_val;
    out_val;
  );

  function follower_delta_func(d) ( d > 0 ? d * c1_charge : d * c1_release );
  function follower_delta_antiderivative1(d) ( d > 0 ? 0.5 * d*d * c1_charge : 0.5 * d*d * c1_release );
  function follower_delta_antiderivative2(d) ( d > 0 ? (1/6) * d*d*d * c1_charge : (1/6) * d*d*d * c1_release );

  function process_channel(input, cap_voltage)
    instance(x_prev, y_prev, d_prev, d_prev2)
    local(filtered_input, abs_input, gate_multiplier, rectified_input, d, delta, diff_d1, diff_d2, diff_d_sum, term1, term2)
  (
    dc_filter ? (
      filtered_input = input - x_prev + dc_block_coeff * y_prev;
      this.x_prev = input;
      this.y_prev = filtered_input;
    ) : (
      filtered_input = input;
    );
 
    abs_input = this.adaa_abs(filtered_input);
    gate_multiplier = (tanh((abs_input - linear_threshold) * sharpness) + 1) * 0.5;
    rectified_input = max(0, abs_input * gate_multiplier + (rand(2) - 1) * linear_noise);
 
    follower_adaa_mode == 0 ? (
      rectified_input > cap_voltage ? (
        cap_voltage = rectified_input + charge_coeff * (cap_voltage - rectified_input);
      ) : (
        cap_voltage = rectified_input + discharge_coeff * (cap_voltage - rectified_input);
      );
    ) : (
      d = rectified_input - cap_voltage;
 
      follower_adaa_mode == 1 ? (
        diff_d1 = d - d_prev;
        delta = (abs(diff_d1) < epsilon) ?
          follower_delta_func((d + d_prev) * 0.5) :
          (follower_delta_antiderivative1(d) - follower_delta_antiderivative1(d_prev)) / diff_d1;
      ) : (
        diff_d1 = d - d_prev;
        term1 = (abs(diff_d1) < epsilon) ?
          follower_delta_antiderivative1((d + d_prev) * 0.5) :
          (follower_delta_antiderivative2(d) - follower_delta_antiderivative2(d_prev)) / diff_d1;
 
        diff_d2 = d_prev - d_prev2;
        term2 = (abs(diff_d2) < epsilon) ?
          follower_delta_antiderivative1((d_prev + d_prev2) * 0.5) :
          (follower_delta_antiderivative2(d_prev) - follower_delta_antiderivative2(d_prev2)) / diff_d2;
 
        diff_d_sum = d - d_prev2;
        delta = (abs(diff_d_sum) < epsilon) ?
          ( (abs(diff_d1) < epsilon) ? follower_delta_func((d+d_prev)*0.5) : (follower_delta_antiderivative1(d) - follower_delta_antiderivative1(d_prev)) / diff_d1 ) :
          2 * (term1 - term2) / diff_d_sum;
      );
 
      this.d_prev2 = d_prev;
      this.d_prev = d;
      cap_voltage += delta;
    );

    cap_voltage *= leakage_coeff;
    cap_voltage;
  );

  function update_coeffs() (
    dc_block_coeff = exp(-2 * $pi * 5 / srate);
    tolerance_factor = 1 + tolerance_pct / 100;
    true_diode_db = diode_db * (1 - tolerance_pct / 200);
    linear_threshold = db_to_lin(true_diode_db);
    knee_width_lin = db_to_lin(true_diode_db) - db_to_lin(true_diode_db - diode_knee_db);
    sharpness = knee_width_lin > epsilon ? 4 / knee_width_lin : 4/epsilon;
 
    true_charge_ms = charge_ms * tolerance_factor;
    true_discharge_ms = discharge_ms * tolerance_factor;
    true_leakage_pct = leakage_pct * tolerance_factor;
 
    charge_coeff = ms_to_coeff(true_charge_ms);
    discharge_coeff = ms_to_coeff(true_discharge_ms);
 
    c1_charge = 1 - charge_coeff;
    c1_release = 1 - discharge_coeff;
 
    leakage_coeff = leakage_to_coeff(max(0, true_leakage_pct));
    linear_noise = noise_onoff ? db_to_lin(noise_db);
  );
 
  capacitor_voltage_L = 0;
  capacitor_voltage_R = 0;
  L.x_prev = 0;
  L.y_prev = 0;
  R.x_prev = 0;
  R.y_prev = 0;
  L.prev_s1 = 0;
  L.prev_s2 = 0;
  R.prev_s1 = 0;
  R.prev_s2 = 0;
  L.d_prev = 0;
  L.d_prev2 = 0;
  R.d_prev = 0;
  R.d_prev2 = 0;
  last_dc_filter_state = dc_filter;
 
  update_coeffs();
 
  pdc_delay = (rect_adaa_mode == 1 ? 0.5 : rect_adaa_mode == 2 ? 1 : 0) +
              (follower_adaa_mode == 1 ? 0.5 : follower_adaa_mode == 2 ? 1 : 0);

@slider
  update_coeffs();
 
  dc_filter != last_dc_filter_state ? (
    L.x_prev = L.y_prev = R.x_prev = R.y_prev = 0;
    last_dc_filter_state = dc_filter;
  );
 
  pdc_delay = (rect_adaa_mode == 1 ? 0.5 : rect_adaa_mode == 2 ? 1 : 0) +
              (follower_adaa_mode == 1 ? 0.5 : follower_adaa_mode == 2 ? 1 : 0);

@sample
  capacitor_voltage_L = L.process_channel(spl0, capacitor_voltage_L);
  capacitor_voltage_R = R.process_channel(spl1, capacitor_voltage_R);

  comp_gain =
    rect_adaa_mode == 0 ? (
      follower_adaa_mode == 0 ? 1.000000 :
      follower_adaa_mode == 1 ? 1.001500 :
                                1.004038
    ) :
    rect_adaa_mode == 1 ? (
      follower_adaa_mode == 0 ? 1.001844 :
      follower_adaa_mode == 1 ? 1.003344 :
                                1.006124
    ) : (
      follower_adaa_mode == 0 ? 1.005779 :
      follower_adaa_mode == 1 ? 1.007283 :
                                1.009724
    );

  output_L = capacitor_voltage_L * comp_gain;
  output_R = capacitor_voltage_R * comp_gain;
 
  monitor_output ? (
    spl0 = output_L;
    spl1 = output_R;
  );


@gfx
  gfx_setfont(1, "Arial", 24);
 
  margin = floor(gfx_texth) * 0.5;
  spacing = margin * 0.5;
 
  sprintf(#capvolt_str, "Capacitor Voltage  =  %.1f dB  |  %.1f dB", lin_to_db(output_L), lin_to_db(output_R) );
 
  gfx_set(1,1,1);
  gfx_x = margin;
  gfx_y = margin;
  gfx_drawstr(#capvolt_str);
 
  bars_y = gfx_y + gfx_texth + spacing;
  bars_max_h = gfx_h - bars_y - margin;
  bar_h = floor((bars_max_h - spacing) / 2);
  max_w = gfx_w - margin * 2;
 
  channel = 0;
  loop(2,
    bar_y = bars_y + channel * (bar_h + spacing);
    bar_w = (channel == 0 ? output_L : output_R) * max_w;
 
    gfx_set(0, 1, 0.7);
    gfx_rect(margin, bar_y, bar_w, bar_h);
 
    channel += 1;
  );

 

Last edited: Jul 2, 2025 at 5:49 PM

I don't know if C++ is a dream stage, but I am quite good at resting if I may say so. I am old, so I have to rest every day and I am particularly good at that. My secret is to go to the bathroom before taking a rest so I don't get waked up by a full bladder. So, lots of experience

 

okay, I get it. you're not sure what C++ is, but you're very rusty

 

I am good at resty because I am very rusty. And I think C++ is the American way of school grades, so C++ is a plus more than a C+ which is of course a + more than a plain C. So you see, you are really a smart person, but I am a clever old fartz

 

I´ve heard your next project has a code name "1073".

 

https://audiosex.pro/attachments/cap_harm-png.58199/
Just a hint for the use of Plugindoctor:
As you can see the frequency is set to 1kHz but the frequency displayed is 2kHz. This happens with samplerate changes. One always has to adjust the fundamental after.

 

This is exactly what you want to see when measuring a full-wave rectifier, right?

 

I don't get it.

 

When you feed a sine wave into a full-wave rectifier, the negative half-cycle of the signal gets "flipped up." This means you now have 2 peaks per period of the original signal, which corresponds to a doubling of the waveform's dominant frequency.
So, 1kHz becomes 2kHz!

Spoiler: See here:

After rectification, we filter the signal to smooth it out a bit and effectively obtain an envelope follower. This is what happens in most detector paths of compressors and meters. The frequency doubling doesn't matter here because we don't hear the signal. It's a control voltage used to drive other processes, for example, to drive the coil of a VU Meter...

Got it?

 

Last edited: Jul 4, 2025 at 10:37 AM

Ah, I see. To me this happens also without a rectifier. Maybe my version is just too old.