message: custom decay curve
diff: @@ -141,7 +141,7 @@ export class Envelope extends ToneAudioNode<EnvelopeOptions> {
  /**
  * The automation curve type for the decay
  */
  - private _decayCurve!: BasicEnvelopeCurve;
  + private _decayCurve!: InternalEnvelopeCurve;
  /**
  * The automation curve type for the release
  @@ -322,12 +322,11 @@ export class Envelope extends ToneAudioNode<EnvelopeOptions> {
  * env.triggerAttack();
  * }, 1, 1);
  */
  - get decayCurve(): BasicEnvelopeCurve {
  - return this._decayCurve;
  + get decayCurve(): EnvelopeCurve {
  + return this._getCurve(this._decayCurve, "Out");
  }
  set decayCurve(curve) {
  - assert(["linear", "exponential"].some(c => c === curve), `Invalid envelope curve: ${curve}`);
  - this._decayCurve = curve;
  + this._setCurve("_decayCurve", "Out", curve);
  }
  /**
  