Peaks voltage ranges for LFO mode, TAP mode, and SEQUENCE mode?

Conrad · May 3, 2017, 10:52pm

Hi, I was just wondering what the voltage ranges are for each of these modes in peaks. I’ve seen /- 8 in some places for LFO and/- 5 in others, so I’d like to know for sure. Also, wondering if the range of the TAP lfo and the range of the sequencer mode is the same?

pichenettes · May 3, 2017, 11:40pm

LFO and tap LFO: /- 5V. It used to be/- 8V before 2015.

Sequencer: +5V.

Conrad · May 4, 2017, 6:40am

Thank you!

migueldetrool · November 9, 2022, 12:37am

Sorry to revive an old topic. I’ve been looking over the Peaks code as I’m looking to modify it so it will make all +/-5V signals to be +/-8V.
For the LFOs, it seems quite straightforward, in lfo.h there are two set_level() that need to be adjusted to 65535 instead of 40960. Same for the mini-sequencer, in the final out line there’s a 40960 to replace.
For the drums however, I can’t find where their level is set in the code. Does anyone have pointers on where to look ?

pichenettes · November 9, 2022, 5:29am

Their peaks are probably at full amplitude already!

migueldetrool · November 9, 2022, 10:00am

Perfect, I thought it would be lower because the specifications say “10Vpp for LFOs and drum signals.”

In that case all is good, are there any other modulations I’m not aware of that don’t use the full range ?

pichenettes · November 9, 2022, 10:05am

I think that’s on average, the click at the onset can be quite high.

If you want, you can try multiply the variable storing the result before it’s CLIPped and written to the output:

github.com

pichenettes/eurorack/blob/master/peaks/drums/bass_drum.cc#L85


      
              int32_t excitation = 0;
              excitation += pulse_up_.Process();
              excitation += !pulse_down_.done() ? 16384 : 0;
              excitation += pulse_down_.Process();
              attack_fm_.Process();
              resonator_.set_frequency(frequency_ + (attack_fm_.done() ? 0 : 17 << 7));
          
          
    int32_t resonator_output = (excitation >> 4) + \
                  resonator_.Process<SVF_MODE_BP>(excitation);
              lp_state_ += (resonator_output - lp_state_) * lp_coefficient_ >> 15;
              int32_t output = lp_state_;
              CLIP(output);
              
              *out++ = output;
            }
          }
          
          
}  // namespace peaks

github.com

pichenettes/eurorack/blob/master/peaks/drums/snare_drum.cc#L100


      
              excitation_2 += !excitation_2_.done() ? 13107 : 0;
          
          
    int32_t body_2 = body_2_.Process<SVF_MODE_BP>(excitation_2) + (excitation_2 >> 4);
              int32_t noise_sample = Random::GetSample();
              int32_t noise = noise_.Process<SVF_MODE_BP>(noise_sample);
              int32_t noise_envelope = excitation_noise_.Process();
              int32_t sd = 0;
              sd += body_1 * gain_1_ >> 15;
              sd += body_2 * gain_2_ >> 15;
              sd += noise_envelope * noise >> 15;
              CLIP(sd);
              *out++ = sd;
            }
          }
          
          
}  // namespace peaks

with one of these:

x = x * 3 >> 1; // for 1.5x gain
x = x * 5 >> 2; // for 1.25x gain

migueldetrool · November 9, 2022, 10:09am

Thank you for the precise info, makes sense. I’ll try it out. Maybe I’ll even get some gnarly distortion going!

Edit: I regrettably do not have an oscilloscope to check exactly, but it does indeed seem like the initial peak of the drums are +/-8V in the original firmware.
For posterity, yes, changing the set_level for the LFOs and the final value in the mini-sequencer out to 65535 does indeed give them full range.