feat(dsp): add FilterFeedbackDelay

packages/dsp/package.json

@@ -154,6 +154,9 @@
 		"./fft": {
 			"default": "./fft.js"
 		},
+		"./filter-delay": {
+			"default": "./filter-delay.js"
+		},
 		"./filter-response": {
 			"default": "./filter-response.js"
 		},

packages/dsp/src/feedback-delay.ts

@@ -5,6 +5,9 @@ import { Delay } from "./delay.js";
  * Extension of {@link Delay} which adds sum delayed value multiplied
  * with `feedback` for each new input.
  *
+ * @remarks
+ * Also see {@link filterFeedbackDelay} for filtered version.
+ *
  * @param n - delay length
  * @param feedback - feedback factor (default: 0.5)
  */

packages/dsp/src/filter-delay.ts

@@ -0,0 +1,42 @@
+import { clamp01 } from "@thi.ng/math/interval";
+import type { IProc } from "./api.js";
+import { Delay } from "./delay.js";
+
+/**
+ * Extension of {@link feedbackDelay} with additional filter/proc
+ * possibility for the feedback itself (e.g. a low pass filter).
+ *
+ * @param n - delay length
+ * @param filter - IProc applied to feedback
+ * @param feedback - feedback factor (default: 0.5)
+ */
+export const filterFeedbackDelay = (
+	n: number,
+	filter: IProc<number, number>,
+	feedback?: number
+) => new FilterFeedbackDelay(n, filter, feedback);
+
+export class FilterFeedbackDelay extends Delay<number> {
+	constructor(
+		n: number,
+		public filter: IProc<number, number>,
+		protected _feedback = 0.5
+	) {
+		super(n, 0);
+		this.setFeedback(_feedback);
+	}
+
+	next(x: number) {
+		return super.next(
+			x + this.filter.next(this._buf[this._rpos] * this._feedback)
+		);
+	}
+
+	feedback() {
+		return this._feedback;
+	}
+
+	setFeedback(feedback: number) {
+		this._feedback = clamp01(feedback);
+	}
+}

packages/dsp/src/index.ts

@@ -18,6 +18,7 @@ export * from "./dcblock.js";
 export * from "./delay.js";
 export * from "./feedback-delay.js";
 export * from "./fft.js";
+export * from "./filter-delay.js";
 export * from "./filter-response.js";
 export * from "./foldback.js";
 export * from "./impulse-train.js";