Microfreak/UG/19 Appendix B Vocoder

• 19. Appendix B: The MicroFreak Vocoder

  • Microfreak/UG/19 Appendix B Vocoder/01 Intro

    • 19.1. An Introduction to Vocoding

      • Bell Labs patented the first vocoder in 1939 to speed up telephone connections. Musical vocoders appeared about forty years later and became known for their robotic sound. Artists have since used them in many ways, from Kraftwerk's “Autobahn” to Imogen Heap's “Hide and Seek.”
      • A vocoder transfers qualities of one sound to another. Speech vowels have characteristic frequency peaks called formants; a vowel commonly has one to three prominent peaks, F1 through F3. The positions of these peaks vary with the speaker and the sound being made.
      • The modulator, usually your voice, supplies the changing formants. A bank of tuned filters analyzes them and applies them to a carrier, such as an oscillator wave. The carrier takes on the shape of your voice.
      • Speech also has a changing loudness contour. The vocoder tracks this contour along with the formants, so the carrier follows the way you articulate a word.
  • Microfreak/UG/19 Appendix B Vocoder/02 How It Works

    • 19.2. How Does Vocoder Work?

      • The MicroFreak analyzes incoming sound with 16 tuned bandpass filters. As with the MicroFreak's own filter in BPF mode, each band emphasizes a limited range of frequencies.
      • An envelope follower tracks the loudness in each band. The resulting signals control matching filters on the carrier, allowing each formant peak to follow its own changing volume. The vocoder also recreates the overall loudness pattern at the end of the signal path.
      • MicroFreak Vocoder signal path
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      • Microfreak/UG/19 Appendix B Vocoder/02 How It Works/01 Resolution

        • 19.2.1. Resolution

          • Early vocoders used roughly 10 frequency bands, which could make speech sound indistinct. The MicroFreak uses 16 bands to recreate the voice more accurately.
      • Microfreak/UG/19 Appendix B Vocoder/02 How It Works/02 Voice

        • 19.2.2. The Perfect Modulator: Your Voice

          • A useful vocoder sound depends on pairing the modulator with a suitable carrier. Speak or sing with clear, even exaggerated articulation to drive the analysis filters.
          • Plosives such as “p,” “t,” and “b,” and sibilants such as “s,” “ch,” and “z,” can confuse the filter banks. The vocoder's high-pass filter helps remove them. Its hiss function can add high-frequency energy to help the filters respond.
      • Microfreak/UG/19 Appendix B Vocoder/02 How It Works/03 Vocoder Osc

        • 19.2.3. The Vocoder Oscillator

          • A carrier rich in overtones gives the vocoder more material to shape. Use the Wave knob to move through sawtooth, pulse width, and noise waves; see also Microfreak/UG/06 Dig Osc/03 Types/22 Vocoder.
          • The Digital Oscillator
            • 
          • Wave positions
            • 0%: sawtooth.
            • Around 11%: pulse wave at 50% duty cycle.
            • From 11% to 90%: increasing pulse width, reaching 97% duty cycle.
            • 91–100%: noise.

          • Note/Info The manual gives different duty cycles at Wave 90%: 97% here and 99% in Microfreak/UG/06 Dig Osc/03 Types/22 Vocoder.
            

          • Sawtooth, pulse-width, and noise waveforms
            • 
          • Timbre and Shape also control the Vocoder Oscillator.

          • Note/Info Oscillator Type cannot be modulated while the Vocoder Oscillator is active.
            

          • Microfreak/UG/19 Appendix B Vocoder/02 How It Works/03 Vocoder Osc/01 Timbre

            • 19.2.3.1. Timbre Encoder

              • Timbre selects the frequency range used for analysis and resynthesis. Vowel formants peak at different frequencies: for example, a “u” may have peaks near 330 and 1260 Hz, with variation across voices.
              • Matching the range to the speaker, or to an instrument used as a modulator, helps the filters respond to the frequencies that matter. Monitoring fewer frequencies can improve response time and output.
              • Vocoder filter bands and frequency response
                • 
          • Microfreak/UG/19 Appendix B Vocoder/02 How It Works/03 Vocoder Osc/02 Shape

            • 19.2.3.2. Shape Encoder

              • Shape sets the bandwidth of each bandpass filter. Higher settings narrow the filters' frequency response and produce more pronounced harmonics.
  • Microfreak/UG/19 Appendix B Vocoder/03 Connect Mic

    • 19.3. Connect the Microphone

      • Insert the microphone unit into the headphone input. Align the black plastic gooseneck adapter with the edges of the MicroFreak case and press gently but firmly. To monitor with headphones, plug them into the output at the microphone base.

      • Note/Info The CTIA/AHJ connector has four segments: tip = left audio, ring 1 = right audio, ring 2 = ground, and sleeve = microphone.
        

      • Note/Info Pull the microphone straight out of the headphone output to avoid damage. Remove it before storing or transporting the MicroFreak.
        

  • Microfreak/UG/19 Appendix B Vocoder/04 Headset Mic

    • 19.4. (Or) Connect a Headset Microphone

      • Insert the headset microphone's 3.5 mm TRRS plug into the MicroFreak headphone jack.

      • Note/Info Use headphones when vocoding. Speakers can feed the vocoder's output back into the microphone and create a feedback loop.
        

  • Microfreak/UG/19 Appendix B Vocoder/05 Vocoder Preset

    • 19.5. Select a Vocoder Preset

      • The MicroFreak Vocoder Limited Edition includes vocoder presets in memory locations 304–320. Turn the Preset knob to select one. A three-step VU meter appears when a vocoder preset is loaded and responds to your voice level.
      • To start from an INIT preset, turn the Digital Oscillator Type knob clockwise and select Vocoder.
      • To save the preset:
        • Click the encoder.
        • Turn it to select the vocoder category.
        • Click it again and optionally name the preset.
        • Click Save.
  • Microfreak/UG/19 Appendix B Vocoder/06 Play & Sing

    • 19.6. Play & Sing

      • Press a key while speaking or singing into the microphone to hear your voice resynthesized by the Vocoder Oscillator. The keyboard determines the output pitch; the vocoder follows the volume and timbre of your voice, not the notes you sing.
      • While playing, adjust the Digital Oscillator's Wave, Timbre, and Shape controls. Turn on Paraphonic mode to vocode chords by playing two or more keys while singing.
  • Microfreak/UG/19 Appendix B Vocoder/07 Config

    • 19.7. Vocoder Configuration

      • The Vocoder settings can be adjusted as the voice or microphone changes. Global Utility settings affect every vocoder preset; settings under Utility > Preset are saved with the current preset.
      • The global settings can be changed on the MicroFreak or in the MIDI Control Center.

      • Mic Settings

        • Mic Gain: -12 dB to +59 dB, or Auto Gain (default).
        • Noise Gate: Off or a threshold; default -70 dB.
        • Mic Detection: Off or On (default).
      • Microfreak/UG/19 Appendix B Vocoder/07 Config/01 Preset Settings

        • 19.7.1. Preset related Vocoder settings

          • Two settings under Utility > Preset are saved with each preset:
            • Vocoder Hiss Mode
            • Vocoder Hiss Vol
          • Older vocoders added high-frequency noise (“hiss”) to the lower, voiced “buzz” range to make consonants easier to understand.

          • Vocoder Hiss Mode

            • Off: Only the lower, vowel-like buzz range is heard.
            • Switched: A detector distinguishes voiced sections from unvoiced sections. During an unvoiced section, white noise replaces the carrier oscillator. Output is gated by the modulator and follows its level.
            • Pass: The vocoded synth signal is mixed with the part of the microphone signal above 5 kHz, allowing the high frequencies of the voice through.

          • Vocoder Hiss Vol

            • Sets the level of hiss mixed with the microphone signal and the white-noise replacement level in Switched mode, from -20 dB to 0 dB.
  • Microfreak/UG/19 Appendix B Vocoder/08 Global Settings

    • 19.8. Global Vocoder settings

      • Use Utility > Mic Settings to match the microphone input to your voice or an external modulator. The menu controls Mic Gain, Noise Gate, and Mic Detection.
      • Auto Gain is the default and suits average use with the Vocoder Edition microphone. A lavalier microphone or external audio source may need manual gain.
      • Microfreak/UG/19 Appendix B Vocoder/08 Global Settings/01 Mic Levels

        • 19.8.1. Setting microphone levels

          • When a vocoder preset is selected, the OLED VU animation shows the microphone input level: Low, Mid, or Skull. Aim for Mid; Skull indicates a level that can distort the vocoder output.
      • Microfreak/UG/19 Appendix B Vocoder/08 Global Settings/02 Gain

        • 19.8.2. What is gain?

          • Microphone signals are usually quiet, around -30 dB to -70 dB, and need amplification. The MicroFreak preamp can reduce or amplify the signal with a gain setting from -12 dB to +59 dB. Negative settings reduce the input; positive settings amplify it.
      • Microfreak/UG/19 Appendix B Vocoder/08 Global Settings/03 Set Gain

        • 19.8.3. How do you set gain?

          • The useful gain depends on how loudly you sing or speak and your distance from the microphone.
          • Set the MicroFreak master volume to about 50%, then use a non-vocoder preset to establish an average listening level.
          • Select the Vocoder Oscillator. Open Utility > Mic Settings > Mic Gain with the Preset encoder. Mic Gain defaults to Auto; turn the encoder left to choose a manual level.
          • Hold a key and speak or sing while adjusting gain until the vocoder is loud enough without distortion. For chords, enable Paraphonic mode and check the level again. Leave headroom if your voice changes volume widely.
          • Microfreak/UG/19 Appendix B Vocoder/08 Global Settings/03 Set Gain/01 Noise Gate

            • 19.8.3.1. Noise Gate

              • When the microphone signal is amplified, background sounds are amplified too. The Noise Gate ignores sounds below its threshold while allowing a louder voice through.
              • Off disables the gate. The default threshold is -70 dB; the detailed setting description gives a range of -30 dB to -98 dB.
          • Microfreak/UG/19 Appendix B Vocoder/08 Global Settings/03 Set Gain/02 Mic Detection

            • 19.8.3.2. Mic detection

              • On is the default. The MicroFreak checks for a microphone whenever a vocoder preset is loaded or the Vocoder Oscillator is selected.
              • If no microphone is detected, the display warns “warning! mic needed”. The mic input is disabled until the next preset loads, and the vocoder filterbank is bypassed, leaving the raw Vocoder Oscillator sound.

              • Note/Info Save a preset as a vocoder-type preset before editing it to keep active microphone-level monitoring.
                

          • Microfreak/UG/19 Appendix B Vocoder/08 Global Settings/03 Set Gain/03 External Sources

            • 19.8.3.3. Connecting external sources

              • An external audio source can modulate the vocoder, including a guitar, drum machine, phone, tablet, or Eurorack mixer. Match its output level to the MicroFreak input: these sources are usually much louder than a microphone.
              • Approximate output levels: microphones -60 to -40 dBU; guitar -20 dBU; phones and tablets -7.78 dBU; Eurorack +13 dBU.
              • Use a headphone/microphone splitter that connects the source to the mic contact of the MicroFreak’s 3.5 mm TRRS jack.
              • Headphone/Microphone Splitter
                • 

              • Note/Info The input uses CTIA/AHJ wiring: tip = left audio, ring 1 = right audio, ring 2 = ground, sleeve = microphone.
                

              • CTIA/AHJ connector
                • 

              • Note/Warning Do not connect a Eurorack module directly to the splitter. Its signal can overload or damage the MicroFreak. Use a mixer headphone or line-level output instead.
                

              • Connect the device

                • Turn off the MicroFreak and gently remove the gooseneck microphone.
                • Turn the external device’s output level all the way down to avoid clipping.
                • Plug the splitter into the MicroFreak headphone jack and the device signal into the splitter’s mic branch.
                • Turn on the MicroFreak.
                • Set Utility > Mic Settings > Mic Detection to Off and Mic Gain initially to -12 dB.
                • Select a vocoder preset, hold a key, and slowly raise Mic Gain. If there is no sound, slowly raise the source device’s output level.
      • Microfreak/UG/19 Appendix B Vocoder/08 Global Settings/04 MIDI Control Center

        • 19.8.4. MIDI Control Center

          • The MIDI Control Center for macOS and Windows can move presets between the MicroFreak and a computer and change MicroFreak settings.
          • Microfreak/UG/19 Appendix B Vocoder/08 Global Settings/04 MIDI Control Center/01 Settings

            • 19.8.4.1. MIDI Control Center settings

              • The global Vocoder settings here match those in the MicroFreak Utility menu.
              • MIDI Control Center Vocoder settings
                • 
              • The software is available from Arturia.
  • Microfreak/UG/19 Appendix B Vocoder/09 Package

    • 19.9. MicroFreak Vocoder Package content

      • The Vocoder Edition package includes:
        • A white MicroFreak case with a swan graphic on the center strip.
        • A gooseneck electret microphone with an adapter/splitter and an added headphone output.
        • A leaflet describing the microphone base and gooseneck.

      • Note/Info A phone headset microphone or clip-on lavalier microphone can also be used if it follows the CTIA/AHJ standard.