message: removing getLevelAtTime
  replaced by onsilence which is used to find when the instrument is making sound
diff: import { FrequencyClass } from "../core/type/Frequency";
  import { Cents, Frequency, NormalRange, Seconds, Time } from "../core/type/Units";
  import { optionsFromArguments } from "../core/util/Defaults";
  +import { noOp } from "../core/util/Interface";
  import { Instrument, InstrumentOptions } from "../instrument/Instrument";
  import { Signal } from "../signal/Signal";
  +type onSilenceCallback = (instrument: Monophonic<any>) => void;
  +
  export interface MonophonicOptions extends InstrumentOptions {
  portamento: Seconds;
  + onsilence: onSilenceCallback;
  }
  /**
  @@ -19,9 +23,9 @@ export abstract class Monophonic<Options extends MonophonicOptions> extends Inst
  portamento: Seconds;
  /**
  - * The instrument's envelope
  + * Invoked when the release has finished and the output is silent.
  */
  - abstract envelope: any;
  + onsilence: onSilenceCallback;
  /**
  * The instrument's frequency signal.
  @@ -40,23 +44,21 @@ export abstract class Monophonic<Options extends MonophonicOptions> extends Inst
  const options = optionsFromArguments(Monophonic.getDefaults(), arguments);
  this.portamento = options.portamento;
  -
  + this.onsilence = options.onsilence;
  }
  static getDefaults(): MonophonicOptions {
  return Object.assign(Instrument.getDefaults(), {
  + onsilence: noOp,
  portamento: 0,
  });
  }
  /**
  * Trigger the attack of the note optionally with a given velocity.
  - *
  - *
  * @param note The note to trigger.
  * @param time When the note should start.
  - * @param velocity The velocity scaler determines how "loud" the note
  - * will be triggered.
  + * @param velocity The velocity scaler determines how "loud" the note will be triggered.
  * @example
  * synth.triggerAttack("C4");
  * @example
  @@ -73,8 +75,7 @@ export abstract class Monophonic<Options extends MonophonicOptions> extends Inst
  /**
  * Trigger the release portion of the envelope
  - * @param {Time} [time=now] If no time is given, the release happens immediatly
  - * @returns {Monophonic} this
  + * @param time If no time is given, the release happens immediatly
  * @example
  * synth.triggerRelease();
  */
  @@ -95,17 +96,6 @@ export abstract class Monophonic<Options extends MonophonicOptions> extends Inst
  */
  protected abstract _triggerEnvelopeRelease(time: Seconds): void;
  - /**
  - * Get the level of the output at the given time. Measures
  - * the envelope(s) value at the time.
  - * @param time The time to query the envelope value
  - * @return The output level between 0-1
  - */
  - getLevelAtTime(time: Time): NormalRange {
  - time = this.toSeconds(time);
  - return this.envelope.getValueAtTime(time);
  - }
  -
  /**
  * Set the note at the given time. If no time is given, the note
  * will set immediately.
  