diff --git a/src/pipeline.ts b/src/pipeline.ts
index fe8d6160..29364ace 100644
--- a/src/pipeline.ts
+++ b/src/pipeline.ts
@@ -17,7 +17,7 @@ import {
   MessageCollector,
   type VoiceBasedChannel,
 } from "discord.js";
-import { SynthesisWorkerPool } from "./synthesis";
+import { synthesizer } from "./synthesis";
 
 export interface StateOptions
   extends CreateVoiceConnectionOptions,
@@ -36,7 +36,6 @@ export default class Pipeline extends EventEmitter {
   public readonly player: AudioPlayer;
   private readonly collector: MessageCollector;
   private audioQueue: AudioResource[] = [];
-  private readonly pool?: SynthesisWorkerPool;
 
   constructor(public readonly channel: VoiceBasedChannel) {
     super();
@@ -53,16 +52,6 @@ export default class Pipeline extends EventEmitter {
       filter: (message) => !message.author.bot,
     });
 
-    if (process.env.DICTIONARY && process.env.MODEL) {
-      this.pool = new SynthesisWorkerPool(
-        process.env.DICTIONARY,
-        process.env.MODEL,
-      );
-      this.pool.on("synthesis", (resource: AudioResource) => {
-        this.emit("synthesis", resource);
-      });
-    }
-
     this.init();
   }
 
@@ -88,6 +77,10 @@ export default class Pipeline extends EventEmitter {
       "collect",
       (message) => void this.emit("message", message),
     );
+    synthesizer.on("synthesis", (resource, message) => {
+      if (message.channelId !== this.channel.id) return;
+      this.emit("synthesis", resource);
+    });
 
     this.on("ready", () => {
       this.play();
@@ -99,11 +92,7 @@ export default class Pipeline extends EventEmitter {
       Pipeline.#cache.delete(this.channel.guild.id);
     });
     this.on("message", (message) => {
-      this.pool?.dispatchSynthesis(
-        message.cleanContent.length > 200
-          ? `${message.cleanContent.slice(0, 196)} 以下略`
-          : message.cleanContent,
-      );
+      synthesizer.dispatchSynthesis(message);
     });
     this.on("synthesis", (audio) => {
       this.audioQueue.push(audio);
diff --git a/src/synthesis/index.ts b/src/synthesis/index.ts
index 58d1114d..f8ec8c78 100644
--- a/src/synthesis/index.ts
+++ b/src/synthesis/index.ts
@@ -1,77 +1,10 @@
-import { Readable } from "node:stream";
-import { StreamType, createAudioResource } from "@discordjs/voice";
-import { AltJTalkConfig } from "node-altjtalk-binding";
-import { Result, Task } from "./common";
-import WorkerPool from "./worker-pool";
+import { Synthesizer } from "./synthesizer";
+import WorkerSynthesizer from "./worker-synthesizer";
 
-export class SynthesisWorkerPool extends WorkerPool<
-  Task,
-  Result,
-  AltJTalkConfig,
-  object
-> {
-  constructor(dictionary: string, model: string) {
-    super(
-      new URL("task", import.meta.url),
-      {
-        dictionary,
-        model,
-      },
-      process.env.NUM_THREADS ? Number(process.env.NUM_THREADS) : 1,
-    );
-    this.on("data", ({ data }: Result) => {
-      const resource = createAudioResource(new SynthesizedSoundStream(data), {
-        inputType: StreamType.Raw,
-      });
-      this.emit("synthesis", resource);
-    });
-  }
-
-  public dispatchSynthesis(inputText: string) {
-    this.dispatchTask(
-      {
-        inputText,
-        option: {
-          samplingFrequency: 48000,
-        },
-      },
-      {},
-    );
-  }
-}
-
-class SynthesizedSoundStream extends Readable {
-  private pos: number = 0;
-  private buf: Int16Array | null;
-  constructor(buf: Int16Array) {
-    super();
-    this.buf = buf;
-  }
-  _read(size: number = ((48000 * 2 * 2) / 1000) * 20) {
-    if (!this.buf) {
-      throw new Error("Stream ended");
-    }
-
-    const offset = this.pos;
-    let end = Math.ceil(size / 4);
-    if (end + offset > this.buf.length) {
-      end = this.buf.length - offset;
-    }
-    const buf = Buffer.alloc(end * 4);
-    const dst = new Int16Array(buf.buffer);
-    for (let i = 0; i < end; ++i) {
-      const elem = this.buf[i + offset];
-      dst[i * 2] = elem;
-      dst[i * 2 + 1] = elem;
-    }
-    this.push(buf);
-    this.pos += end;
-    if (this.pos == this.buf.length) {
-      this.buf = null;
-      this.push(null);
-    }
-  }
-  _destroy() {
-    this.buf = null;
-  }
+if (!process.env.DICTIONARY || !process.env.MODEL) {
+  throw new Error("Dictionary and model must be specified.");
 }
+export const synthesizer: Synthesizer = new WorkerSynthesizer(
+  process.env.DICTIONARY,
+  process.env.MODEL,
+);
diff --git a/src/synthesis/options.ts b/src/synthesis/options.ts
new file mode 100644
index 00000000..943e0f34
--- /dev/null
+++ b/src/synthesis/options.ts
@@ -0,0 +1,6 @@
+import { Message } from "discord.js";
+import { SynthesisOption } from "node-altjtalk-binding";
+
+export function createSynthesisOption(_: Message): SynthesisOption {
+  return {};
+}
diff --git a/src/synthesis/stream.ts b/src/synthesis/stream.ts
new file mode 100644
index 00000000..02b99155
--- /dev/null
+++ b/src/synthesis/stream.ts
@@ -0,0 +1,37 @@
+import { Readable } from "node:stream";
+
+export default class SynthesizedSoundStream extends Readable {
+  private pos: number = 0;
+  private buf: Int16Array | null;
+  constructor(buf: Int16Array) {
+    super();
+    this.buf = buf;
+  }
+  _read(size: number = ((48000 * 2 * 2) / 1000) * 20) {
+    if (!this.buf) {
+      throw new Error("Stream ended");
+    }
+
+    const offset = this.pos;
+    let end = Math.ceil(size / 4);
+    if (end + offset > this.buf.length) {
+      end = this.buf.length - offset;
+    }
+    const buf = Buffer.alloc(end * 4);
+    const dst = new Int16Array(buf.buffer);
+    for (let i = 0; i < end; ++i) {
+      const elem = this.buf[i + offset];
+      dst[i * 2] = elem;
+      dst[i * 2 + 1] = elem;
+    }
+    this.push(buf);
+    this.pos += end;
+    if (this.pos == this.buf.length) {
+      this.buf = null;
+      this.push(null);
+    }
+  }
+  _destroy() {
+    this.buf = null;
+  }
+}
diff --git a/src/synthesis/synthesizer.ts b/src/synthesis/synthesizer.ts
new file mode 100644
index 00000000..deac56cb
--- /dev/null
+++ b/src/synthesis/synthesizer.ts
@@ -0,0 +1,14 @@
+import { AudioResource } from "@discordjs/voice";
+import { Message } from "discord.js";
+
+export interface Synthesizer {
+  dispatchSynthesis(message: Message): void;
+  on<K extends keyof SynthesizerEvents>(
+    event: K,
+    listener: (...args: SynthesizerEvents[K]) => void,
+  ): this;
+}
+
+export interface SynthesizerEvents {
+  synthesis: [resource: AudioResource, message: Message];
+}
diff --git a/src/synthesis/worker-pool.ts b/src/synthesis/worker-pool.ts
index 56d63922..b28ed420 100644
--- a/src/synthesis/worker-pool.ts
+++ b/src/synthesis/worker-pool.ts
@@ -1,3 +1,4 @@
+/* eslint-disable @typescript-eslint/no-unsafe-declaration-merging */
 // Reference: https://nodejs.org/api/async_context.html#using-asyncresource-for-a-worker-thread-pool
 
 import { EventEmitter } from "node:events";
@@ -56,7 +57,7 @@ export default class WorkerPool<
       const prop = this.workerInfo.get(worker.threadId);
       if (!prop) return;
 
-      this.emit("data", result);
+      this.emit("data", result, prop);
       this.workerInfo.delete(worker.threadId);
 
       this.freeWorkers.push(worker);
@@ -77,7 +78,7 @@ export default class WorkerPool<
     this.emit(kWorkerFreedEvent);
   }
 
-  protected dispatchTask(task: Task, prop: TaskProperty) {
+  public dispatchTask(task: Task, prop: TaskProperty) {
     const worker = this.freeWorkers.pop();
     if (!worker) {
       // No free threads, wait until a worker thread becomes free.
@@ -93,3 +94,35 @@ export default class WorkerPool<
     for (const worker of this.workers) await worker.terminate();
   }
 }
+
+export default interface WorkerPool<
+  // eslint-disable-next-line @typescript-eslint/no-unused-vars
+  Task,
+  Result,
+  // eslint-disable-next-line @typescript-eslint/no-unused-vars
+  WorkerData,
+  TaskProperty extends object,
+> {
+  on<K extends keyof WorkerPoolEvents<Result, TaskProperty>>(
+    event: K,
+    listener: (...args: WorkerPoolEvents<Result, TaskProperty>[K]) => void,
+  ): this;
+  once<K extends keyof WorkerPoolEvents<Result, TaskProperty>>(
+    event: K,
+    listener: (...args: WorkerPoolEvents<Result, TaskProperty>[K]) => void,
+  ): this;
+  off<K extends keyof WorkerPoolEvents<Result, TaskProperty>>(
+    event: K,
+    listener: (...args: WorkerPoolEvents<Result, TaskProperty>[K]) => void,
+  ): this;
+  emit<K extends keyof WorkerPoolEvents<Result, TaskProperty>>(
+    event: K,
+    ...args: WorkerPoolEvents<Result, TaskProperty>[K]
+  ): boolean;
+}
+
+export interface WorkerPoolEvents<Result, TaskProperty> {
+  data: [result: Result, prop: TaskProperty];
+  error: [error: unknown];
+  [kWorkerFreedEvent]: [];
+}
diff --git a/src/synthesis/worker-synthesizer.ts b/src/synthesis/worker-synthesizer.ts
new file mode 100644
index 00000000..384e27e7
--- /dev/null
+++ b/src/synthesis/worker-synthesizer.ts
@@ -0,0 +1,73 @@
+/* eslint-disable @typescript-eslint/no-unsafe-declaration-merging */
+import EventEmitter from "events";
+import { StreamType, createAudioResource } from "@discordjs/voice";
+import { Message } from "discord.js";
+import { AltJTalkConfig } from "node-altjtalk-binding";
+import { Result, Task } from "./common";
+import { createSynthesisOption } from "./options";
+import SynthesizedSoundStream from "./stream";
+import { Synthesizer, SynthesizerEvents } from "./synthesizer";
+import WorkerPool from "./worker-pool";
+
+export default class WorkerSynthesizer
+  extends EventEmitter
+  implements Synthesizer
+{
+  workerPool: WorkerPool<Task, Result, AltJTalkConfig, Message>;
+
+  constructor(dictionary: string, model: string) {
+    super();
+    this.workerPool = new WorkerPool(
+      new URL("task", import.meta.url),
+      {
+        dictionary,
+        model,
+      },
+      process.env.NUM_THREADS ? Number(process.env.NUM_THREADS) : 1,
+    );
+    this.workerPool.on("data", ({ data }: Result, message) => {
+      const resource = createAudioResource(new SynthesizedSoundStream(data), {
+        inputType: StreamType.Raw,
+      });
+      this.emit("synthesis", resource, message);
+    });
+  }
+
+  public dispatchSynthesis(message: Message) {
+    const inputText =
+      message.cleanContent.length > 200
+        ? `${message.cleanContent.slice(0, 196)} 以下略`
+        : message.cleanContent;
+    const option = createSynthesisOption(message);
+
+    this.workerPool.dispatchTask(
+      {
+        inputText,
+        option: {
+          ...option,
+          samplingFrequency: 48000,
+        },
+      },
+      message,
+    );
+  }
+}
+
+export default interface WorkerSynthesizer {
+  on<K extends keyof SynthesizerEvents>(
+    event: K,
+    listener: (...args: SynthesizerEvents[K]) => void,
+  ): this;
+  once<K extends keyof SynthesizerEvents>(
+    event: K,
+    listener: (...args: SynthesizerEvents[K]) => void,
+  ): this;
+  off<K extends keyof SynthesizerEvents>(
+    event: K,
+    listener: (...args: SynthesizerEvents[K]) => void,
+  ): this;
+  emit<K extends keyof SynthesizerEvents>(
+    event: K,
+    ...args: SynthesizerEvents[K]
+  ): boolean;
+}