# USB-HEAR — Full Architecture, Interface & Technical Reference > Complete technical documentation for [USB-HEAR](https://usb-hear.com) by [FibreCode GmbH](https://www.fibrecode.com). > Website: [https://usb-hear.com](https://usb-hear.com) > Contact: [info@fibrecode.com](mailto:info@fibrecode.com) | Phone: +49 (0)151 2716 1688 > Location: FibreCode GmbH, Marie-Curie-Straße 9, 76275 Ettlingen, Germany --- ## 1. System Architecture Overview USB-HEAR is an advanced digital audio receiver platform developed by FibreCode GmbH that bridges high-speed USB 2.0 host computers (Windows, macOS, Linux, Android, iOS) with audiophile Digital-to-Analog Converters (DACs) and digital signal processors. ### Architecture Highlights - **Core Controller:** NXP i.MXRT1064 crossover MCU based on the Arm Cortex-M7 core operating at 600 MHz, featuring 4 MB on-chip Flash and 1 MB high-speed TCM SRAM. - **USB Interface:** USB 2.0 High-Speed (480 Mbps) Isochronous endpoint architecture compliant with USB Audio Class 2.0 (UAC 2.0). - **Asynchronous Audio Clocking:** The module requests host audio data dynamically using an asynchronous feedback endpoint, locking audio reconstruction entirely to local, ultra-low phase noise master clocks instead of the noisy USB SOF (Start-of-Frame) clock. - **Clock Domain Support:** - 44.1 kHz family (44.1, 88.2, 176.4, 352.8, 705.6 kHz / DSD64 to DSD1024) driven by 22.5792 MHz or 45.1584 MHz master oscillators. - 48 kHz family (48, 96, 192, 384, 768 kHz) driven by 24.576 MHz or 49.152 MHz master oscillators. - Automatic oscillator switching via dedicated GPIO output control lines. --- ## 2. Audio Formats & Sampling Rates | Audio Format | Resolution / Data Rate | Sample Rates | Mode / Protocol | | :--- | :--- | :--- | :--- | | **PCM Stereo** | 16-bit, 24-bit, 32-bit | 44.1, 48, 88.2, 96, 176.4, 192, 352.8, 384, 705.6, 768 kHz | I2S Standard / Left-Justified | | **Native DSD** | 1-bit bitstream | DSD64, DSD128, DSD256, DSD512, DSD1024 | Native DSD bitstream over I2S data lines | | **DoP (DSD over PCM)** | 24-bit PCM container | DSD64 (176.4 kHz), DSD128 (352.8 kHz), DSD256 (705.6 kHz) | Standard DoP V1.1 marker framing | | **SPDIF / TOSLINK** | 16-bit to 24-bit stereo | 44.1, 48, 88.2, 96, 176.4, 192 kHz | IEC 60958-3 consumer frame output | --- ## 3. Hardware Products & Specifications ### 3.1 FC301 USB-HEAR Module - **Form Factor:** Compact SMT System-on-Module with castellated edge pads. - **Size:** Approx. 33 mm × 33 mm. - **Supply Voltages:** 3.3 V I/O and core power rails; optional 5 V VBUS sensing. - **Outputs & Pins:** - `MCLK` (Master Clock input from external crystal oscillators) - `BCLK` (Bit Clock output) - `LRCLK` / `WCLK` (Frame / Word Clock output) - `SDATA_OUT` (PCM Serial Data / DSD Data L) - `DSD_R` (DSD Data R / DSD status indicator) - `DSD_ON` (Hardware flag indicating active DSD streaming mode) - `MUTE` (Hardware automute output to suppress pop/click transients) - `FREQ_SEL` (Oscillator bank selector: 44.1 kHz vs 48 kHz family) - `I2C_SCL` / `I2C_SDA` (Host/slave communication for DAC register initialization) - `SPDIF_TX` (Direct digital bi-phase mark encoded audio output) ### 3.2 FC920 USB-HEAR DevKit - **Form Factor:** Raspberry Pi 3A+ mechanical form factor (65 mm × 56 mm) with standard mounting hole pattern. - **Header:** 40-pin GPIO female header with standard Raspberry Pi I2S pin allocation: - Pin 12: BCLK (Bit Clock) - Pin 35: LRCLK (Word Clock) - Pin 40: DOUT (PCM Data) - Pins 3 & 5: I2C (SDA, SCL) - Pins 1 & 17: 3.3 V Power - Pins 2 & 4: 5 V Power - Pins 6, 9, 14, 20, 25, 30, 34, 39: Ground - **Audio HAT Compatibility:** Plug-and-play with commercially available Raspberry Pi Audio DAC HATs (e.g., PCM5122, ESS Sabre ES9038Q2M, AKM AK4493 boards). - **Connectors:** USB Type-C receptacle, Optical TOSLINK transmitter, power header, debug header. ### 3.3 Design-In Licensing - Complete production-ready Altium Designer schematics and PCB layout snippets. - Thesycon Windows ASIO driver package with custom vendor branding, signing, and installer. - Custom firmware features (e.g. customized I2C DAC initialization sequences, OLED display telemetry, volume curve tailoring). --- ## 4. Software & Driver Architecture ### Operating System Compatibility - **Windows 10 & 11:** - Standard UAC 2.0 WASAPI audio out-of-the-box. - Dedicated FibreCode / Thesycon ASIO 2.2 driver for bit-perfect low-latency Native DSD up to DSD1024 and 768 kHz PCM. - **macOS (OS X 10.6.8 and later):** - Completely driverless operation via CoreAudio. - Bit-perfect playback with Audirvana, Roon, HQPlayer, and Apple Music. - **Linux (Kernel 3.8 and later):** - Native ALSA support (snd-usb-audio driver). - Bit-perfect streaming with MPD, Volumio, Moode Audio, Roon Bridge. - **Mobile (iOS, iPadOS, Android):** - USB OTG / USB-C plug-and-play without driver installation. --- ## 5. Technical Documentation Links - **Data Sheet – FC301 USB-HEAR-Module V01-02-00:** [https://usb-hear.com/assets/pdf/DS_FC301_USB-HEAR-Module_V01-02-00.pdf](https://usb-hear.com/assets/pdf/DS_FC301_USB-HEAR-Module_V01-02-00.pdf) - **Product Flyer – FC301 USB-HEAR-Module V01-02-00:** [https://usb-hear.com/assets/pdf/PF_FC301_USB-HEAR-Module_V01-02-00.pdf](https://usb-hear.com/assets/pdf/PF_FC301_USB-HEAR-Module_V01-02-00.pdf) - **Product Flyer – FC920 USB-HEAR-DevKit V01-02-00:** [https://usb-hear.com/assets/pdf/PF_FC920_USB-HEAR-DevKit_V01-02-00.pdf](https://usb-hear.com/assets/pdf/PF_FC920_USB-HEAR-DevKit_V01-02-00.pdf) - **User Manual – FC920 USB-HEAR-DevKit V01-02-00:** [https://usb-hear.com/assets/pdf/UM_FC920_USB-HEAR-DevKit_V01-02-00.pdf](https://usb-hear.com/assets/pdf/UM_FC920_USB-HEAR-DevKit_V01-02-00.pdf) --- ## 6. Contact & Engineering Inquiries - **Platform Inquiries & Sample Requests:** [https://usb-hear.com/#contact](https://usb-hear.com/#contact) - **General Inquiries:** [info@fibrecode.com](mailto:info@fibrecode.com) - **Phone:** +49 (0)151 2716 1688 - **Address:** FibreCode GmbH, Marie-Curie-Straße 9, 76275 Ettlingen, Germany - **Corporate Website:** [https://www.fibrecode.com](https://www.fibrecode.com) - **Hardware Store:** [https://store.fibrecode.com](https://store.fibrecode.com)