【Deep Abyss Audio】(1) Design & Specs: Building a Pro‑Audio USB DAC with an ESP32‑S3 Core (DIY)

Good evening. Starting today, we dive into the world of hand‑built USB DACs.

As you can see in the photo, the goal is to build a Pro Audio–grade USB DAC using this simple configuration. And yes… I’ll try to make the explanation as easy to follow as possible.

…Still, it looks pretty bare‑bones, doesn’t it?

Here’s the main architecture—nothing unusual at first glance:

Specs

“So what exactly makes this a Pro Audio design?”

Let’s jump straight into the goals and target performance.

Control: USB mount, stream open/close, mute, volume

Supported Hosts: Windows / Mac / Android / iPhone

Quality: Ultra‑low jitter, low latency, real‑time playback priority

Enclosure: Portable, USB‑powered, no battery

“Wait… can an ESP32‑S3 PCM5102A really achieve all that?”

“What about MCLK?”

If you’re thinking that—don’t worry. Yes, it’s achievable. And we’ll do it without any external master clock.

Control Architecture

Let’s start by looking at the functional flow of a typical USB DAC.

Before going deeper, let’s briefly review how a USB DAC works.

In general terms, the host (PC or smartphone) sends digital audio (PCM) over USB using the USB clock. The DAC, however, needs PCM delivered according to the I2S clock. If the data is converted correctly and transmitted over I2S, the USB DAC does its job.

Two clocks appear here—like the left and right wheels of the system:

- USB clock — ultimately derived from the audio host

- I2S clock — directly affects the DAC’s timing

Are these two clocks “perfectly synchronized as if they were one”?

The answer is no.

In this architecture—and in most USB DACs—there are effectively two independent GMTs. To deliver clean PCM data to the DAC, you need a clock compensation controller between them.

If you’ve used a USB DAC on Windows, you might think:

“Windows lets me choose the DAC’s sample rate and bit depth!”

“So if I match everything perfectly, the clocks should be synchronized and the audio should be pristine!”

If that’s your assumption—and if you want Pro Audio quality, deeper understanding, and reliable playback even on iPhone—it’s time to let go of that idea.

This is exactly why the PCM2704 era ended, and why XMOS (and similar chips) became essential.

Since we’re aiming for Pro Audio performance, the plan is to embed XMOS‑class functionality into the ESP32‑S3 as far as possible.

Checking the ESP32‑S3 Specs

For the “pseudo‑MOS” core, I chose the XAIO ESP32‑S3 for its responsiveness, certification, and practical performance.

The ESP32‑S3 supports USB‑OTG mode (USB 1.0/1.1 full‑speed).

(UAC is a protocol, so the ESP32‑S3 can communicate with both UAC1.0 and UAC2.0.)

For DAC clocking, the ESP32 offers PLL 160 MHz and XTAL 40 MHz as internal master clock sources.

GPIO pins required:

- USB: D / D−

- DAC: MCLK, BCLK, LRCK, DOUT

- Display: SDA, SCL

- Debug serial: 2 pins

Total: 10 pins, all available on the XAIO module.

Power:

- USB/DAC 5V (with onboard 3.3V regulator)

- OLED 3.3V

- 5V from USB, 3.3V from XAIO distribution

Software Architecture

The controller software for the pseudo‑MOS core will of course run on the ESP32‑S3.

Development environment:

- IDE: Visual Studio Code

- Environment: PlatformIO

- Target: XAIO ESP32‑S3

- Platform: Espressif32

- Framework: ESP‑IDF 5.5.0 (2nd stage)

- Components:

  - SSD1306 library (robotcantalk.blogspot.com)

  - TinyUSB (tinyusb.org)

You might ask:

“Shouldn’t we use USB Device UAC if we’re doing UAC?”

USB Device UAC supports UAC2.0 High‑Speed and is nearly full‑spec. However… it cannot reach the Pro Audio performance we’re aiming for. So we won’t use it.

Meaning: We will fully implement UAC procedures and USB responses ourselves. Otherwise… it simply wouldn’t be a proper pseudo‑MOS.

Next Time

Next time, we’ll dive into the basic architecture of the pseudo‑MOS and begin with the master clock generation.