HubAudio/docs/architecture/HubAudio-System-Architecture.md

HubAudio System Architecture

• Status: Draft
• Date: 2026-08-01
• Document Type: System Architecture

1. Overview

HubAudio is a modular digital audio platform designed around a centralized Audio Domain architecture.

The system separates three main functional areas:

• Control Domain
• Audio Domain
• Clock Distribution Layer

Each area has a clearly defined responsibility.

The architecture is based on the principle:

System Controller System Controller manages the Control Domain.

Audio Processor Audio Processor manages the Audio Domain.

The Clock Distribution Layer provides the synchronization reference for all digital audio peripherals.

The Audio Processor acts as the timing and routing authority of the digital audio infrastructure, while the System Controller provides supervision, connectivity and configuration management.

2. High Level Architecture

                 HUBAUDIO


            CONTROL DOMAIN

         System Controller System Controller

      Network / UI / Configuration

                   |

                   |

                  SPI

                   |

    +--------------+--------------+

    |                             |

Audio Processor Audio Processor Radio Receiver Radio Receiver

    |
    |
    |
 AUDIO DOMAIN

Audio Sources:

System Controller System Controller Radio Receiver Radio Receiver Bluetooth Receiver Optical Input

    |

    |

Audio Processing

DSP / Routing / Mixing

    |

    |

Audio Destinations:

CODEC/DAC Bluetooth Transmitter Optical Output

                   |

                   |

      CLOCK DISTRIBUTION LAYER

                   |

          MCLK / BCLK / LRCLK

3. Functional Domains

3.1 Control Domain

The Control Domain is responsible for system management.

Main component:

System Controller

Responsibilities:

• network connectivity
• streaming services
• user interface
• configuration management
• firmware update coordination
• device supervision

Communication:

System Controller

|

SPI

|

Audio peripherals

The Control Domain does not transport real-time audio.

---

3.2 Audio Domain

The Audio Domain is centered around the Audio Processor.

The Audio Processor is responsible for:

• DSP processing
• audio routing
• mixing
• digital effects
• format conversion
• audio synchronization

Audio sources:

System Controller Radio Receiver Bluetooth RX Optical Input

Audio destinations:

CODEC/DAC Bluetooth TX Optical Output

The audio transport uses:

I2S

---

3.3 Time Domain

The Time Domain provides the synchronization reference.

The Audio Processor is the audio clock master.

The clock distribution provides:

• MCLK
• BCLK
• LRCLK

Clock distribution:

         Audio Processor

     Audio Clock Master

            |

            |

      Clock Buffer

            |

+-----------+-----------+

|           |           |

CODEC Radio Receiver BT

---

4. Component Roles

System Controller

Role:

System Controller + Audio Source

Functions:

• network audio streaming
• system management
• configuration

Inside Audio Domain:

I2S Source

---

Audio Processor

Role:

Audio Domain Master

Functions:

• DSP
• routing
• mixing
• clock generation

Interfaces:

SPI -> Configuration I2S -> Audio Clock -> Synchronization

---

Radio Receiver

Role:

Digital Radio Audio Source

Functions:

• FM reception
• DAB/DAB+
• digital audio output

Interfaces:

SPI -> Control

I2S -> Audio

---

Bluetooth Modules

Role:

Wireless Audio Interfaces

Bluetooth RX:

BT Audio

|

I2S

|

Audio Processor

Bluetooth TX:

Audio Processor

|

I2S

|

BT Transmitter

---

Digital Converters

Optical interfaces are handled through dedicated conversion stages.

Input:

SPDIF

|

DECODEC

|

I2S

|

Audio Processor

Output:

Audio Processor

|

I2S

|

ENCODEC

|

SPDIF

---

5. Design Philosophy

HubAudio follows a distributed intelligence model.

The System Controller provides connectivity and supervision.

The Audio Processor provides audio intelligence.

Dedicated peripherals provide specialized functions.

The architecture avoids making the microcontroller responsible for time-critical audio processing.

---

6. Expansion Strategy

The architecture allows future integration of:

• additional audio sources
• additional DSP processing
• microphones
• sensors
• alternative wireless interfaces

Expansion follows the same principle:

Control:

SPI

Audio:

I2S

Synchronization:

Clock Domain

---

7. Summary

HubAudio is structured around three independent but coordinated planes:

CONTROL PLANE

System Controller | SPI

AUDIO PLANE

Audio Processor | I2S

TIME PLANE

Audio Processor | Clock Distribution

This separation defines the fundamental architecture of HubAudio.