TheStreamDeck
A Raspberry Pi-based unified streaming audio appliance. One device, one amp input, instant source switching, album art on screen, and physical analogue VU meters.
The Problem
Too many sources, too much friction
An audiophile with multiple streaming subscriptions — Tidal HiFi Plus, Plexamp (local library), BBC 6 Music, internet radio — experiences frustrating, slow source switching when listening through a high-quality integrated amplifier. Each service runs on a different device, requiring manual amp input selection.
The fragmented workflow disrupts listening sessions, adds unnecessary physical interaction, and wastes the visual potential of album artwork during playback.
Switching between audio sources requires changing physical devices and amp inputs — slow, disruptive, and frustrating. No unified device exists that consolidates all streaming sources into a single digital output with instant switching.
- Each source = different device
- Manual amp input switching
- No album art during playback
- Broken listening flow
- Underuse of paid subscriptions
The Solution
One device, one input, instant switching
TheStreamDeck consolidates BBC 6 Music, Tidal HiFi Plus, Plexamp, and internet radio into a single Raspberry Pi 4 appliance with a touchscreen, physical source buttons, real-time VU meter visualisation, and S/PDIF digital output to an integrated amplifier.
4 Sources, 1 Output
BBC 6 Music (MPD), Tidal HiFi Plus (Tidal Connect), Plexamp (headless), and internet radio — all routed through PipeWire to a single S/PDIF optical output.
< 3 Second Switching
Physical buttons and touchscreen for instant source selection. A Rust daemon manages source lifecycle — stop current, start new, update UI. No amp input changes needed.
Audio Sources
Four sources, unified
| Source | Quality | Details |
|---|---|---|
| BBC 6 Music | 320kbps AAC | MPD player, HLS stream. ICY metadata for now-playing info. |
| Tidal HiFi Plus | Lossless FLAC 24/96 | Tidal Connect via Podman. Cast from phone, Pi renders audio. |
| Plexamp | FLAC (local library) | Headless Node.js player. Cast-based control from any client. |
| Internet Radio | Variable | MPD with preset stations. Shoutcast, Icecast, HLS streams. |
Hardware Architecture
Purpose-built audio appliance
| Component | Name | Details |
|---|---|---|
| Compute | Raspberry Pi 4 Model B | Quad A72 @ 1.5GHz, VideoCore VI GPU. PiOS Lite 64-bit. Wired Ethernet for reliability. |
| Digital Transport | HiFiBerry Digi2 Pro | S/PDIF output (TOSLINK optical + coax). Dual oscillator, low jitter. 192kHz/24-bit. NOT a DAC — pure digital transport. |
| Display | 5" Touchscreen | IPS capacitive touch. HDMI + USB (no GPIO conflict). Fits 70mm case height to match amplifier form factor. |
| VU Meter DAC | MCP4922 | Dual 12-bit SPI DAC driving L/R analogue panel meters. 4096 steps, zero jitter. Powered from Pi's 3.3V rail. |
| VU Meters | Analogue Panel Meters | Moving-coil needle meters. Software VU ballistics (300ms IIR filter). Series resistor + trim pot per channel for calibration. |
| Amplifier | NAD C 3xx Series | Optical digital input, Cirrus Logic internal DAC. All D/A conversion happens in the amp — the Pi stays purely digital. |
Signal Path
Streaming Source (Tidal / Plexamp / MPD)
|
v
PipeWire (audio server / multiplexer)
|
+---> HiFiBerry Digi2 Pro (I2S -> S/PDIF)
| |
| +---> TOSLINK optical cable
| |
| v
| Amplifier optical input
| |
| v
| Internal DAC (D/A conversion)
| |
| v
| Amplifier stage -> Speakers
|
+---> PipeWire monitor source (audio tap)
|
v
VU Meter / Spectrum (cpal + RustFFT -> display + MCP4922)
Why Digi HAT, not DAC HAT: The Pi stays purely digital — no analogue stages on the Pi side. The amplifier's Cirrus Logic DAC is purpose-built with dedicated power regulation and shielding. Using a DAC HAT would mean unnecessary double conversion (digital -> HAT DAC -> analogue -> amp). TOSLINK optical provides galvanic isolation, eliminating ground loop hum from the Pi's switching PSU.
User Interface
Touchscreen + physical controls
The UI renders via Rust + Slint (GPU-accelerated, OpenGL ES on VideoCore VI). No X11 or Wayland — direct framebuffer rendering. The display shows album artwork, VU meters, now-playing metadata, source buttons, and transport controls.
+-----------------------------------------------------------------------+
| |
| +---------------------------+ +----------------------------------+ |
| | | | | |
| | Album Artwork | | VU Meter / Spectrum | |
| | (600x600) | | Visualisation | |
| | | | (L + R) | |
| +---------------------------+ +----------------------------------+ |
| |
| +-----------------------------------------------------------------+ |
| | Track: Song Title Artist Name | |
| | Album: Album Title FLAC 24/96 | |
| +-----------------------------------------------------------------+ |
| |
| [ BBC ] [ TDAL ] [ PLEX ] [ RDIO ] [<<] [ > / || ] [>>] |
| |
+-----------------------------------------------------------------------+
Physical buttons mirror the touchscreen sources (GPIO-connected). A rotary encoder provides volume control. All controls work with the display off.
Design Decisions
Why it works this way
-
Digital transport over DAC HAT — The amplifier's internal Cirrus Logic DAC is objectively superior to any ~$30 Pi HAT DAC. Keeping the Pi purely digital avoids double D/A conversion and eliminates ground loop hum via TOSLINK galvanic isolation. The HiFiBerry Digi2 Pro provides bit-perfect S/PDIF with dual oscillators for low jitter.
-
MCP4922 SPI DAC for VU meters over PWM — Hardware PWM on GPIO 18 conflicts with the HiFiBerry's PCM_CLK. Software PWM produces visible needle jitter (~13 usable steps). The MCP4922 gives 4096 steps with zero jitter via SPI — proven superior in head-to-head testing. Total cost: ~$4 for the IC.
-
PipeWire as the audio multiplexer — PipeWire is the default audio server on PiOS Bookworm. It natively multiplexes all sources (MPD, Tidal Connect, Plexamp) into a single output. Monitor sources provide an audio tap for VU meter visualisation without affecting the main signal path.
-
Rust + Slint for the UI — Purpose-built for embedded touchscreens. GPU-accelerated via OpenGL ES on VideoCore VI. Works with framebuffer directly — no X11/Wayland needed. Keeps the entire codebase in Rust. VU meter renders at 60fps with ~8-15% CPU overhead.
-
Cast-based control model for Tidal and Plexamp — The Pi is the renderer, not the controller. Tidal Connect and Plexamp both support cast-based playback — control from your phone, audio plays through the Pi. This avoids building complex playback UIs and leverages the native apps' full feature sets.
-
435mm width form factor — Designed to match the NAD C 3xx amplifier width. The case height is locked to 70mm (matching the NAD C 338 profile). This constrains the display to 5" max and the VU meters to 45-50mm — deliberate trade-offs for visual coherence in the listening position.
-
Software VU ballistics over mechanical damping — A 300ms IIR filter in software implements VU-standard ballistics (1-1.5% overshoot). Budget analogue meters have poor mechanical damping, so software compensation is essential. Higher-quality meters can rely on their own inertia with only a gentle 50ms smoothing pass.
Evolution
How it took shape
v0.1.0 — 4 April 2026 — Problem Statement & Technical Specification
- Architecture: Hardware architecture designed: Pi 4B + HiFiBerry Digi2 Pro + NAD optical input. First-principles analysis confirmed Digi HAT over DAC HAT. Software stack defined: PiOS Lite, PipeWire, MPD, Tidal Connect (Podman), Plexamp headless.
- Added: Source switching architecture with Rust daemon + Slint UI. VU visualisation pipeline: cpal + RustFFT (NEON-accelerated on aarch64). Architecture diagram Rev A. 758-line research file.
v0.2.0 — 5 April 2026 — VU Meter Subsystem & Display Upgrade
- Added: MCP4922 dual SPI DAC circuit designed. KiCad schematic authored. VU meter driver wiring defined with series resistor + trim pot calibration. Printable screen templates for UI sketching.
- Changed: Display upgraded from 7" DSI (720p) to 13.3" HDMI (1080p). UI layout updated for full HD canvas. GPIO allocation revised for SPI DAC. BOM updated.
v0.3.0 — 5 April 2026 — Form Factor & Industrial Design
- Changed: Display revised from 13.3" to 5" to fit 70mm case height matching amplifier form factor. VU meters resized from 85mm to 45-50mm. Case width locked to 435mm (standard hi-fi component width).
- Added: Front panel concept diagram. Blank wireframe PDFs for sketching. Case wireframe PDFs with four VU meter layout options (circular + rectangular).
Build Plan
Five phases to first sound
- Audio Foundation (Week 1) — PiOS setup, PipeWire config, HiFiBerry Digi2 Pro I2S output. MPD playing BBC 6 Music through TOSLINK. First sound through the amplifier.
- All Sources Online (Week 2) — Tidal Connect container, Plexamp headless, internet radio presets. Source Controller daemon with GPIO button switching. <3s switching verified.
- Display & UI (Week 3) — Touchscreen integration. Slint UI with album art, now-playing, source buttons, transport controls. Metadata retrieval from all sources.
- VU Meters (Week 4) — MCP4922 wiring and driver. cpal audio capture from PipeWire monitor. RustFFT analysis. Software ballistics. Physical meter calibration.
- Case & Polish (Week 5) — 435mm x 70mm enclosure. Component mounting. Cable management. Boot optimisation. Final integration testing.
Current Status
Hardware architecture, VU meter circuit design (KiCad schematic), form factor, and software stack are fully specified. The project is ready to begin Phase 1 (audio foundation) once the hardware is assembled. Key components: Pi 4B (owned), HiFiBerry Digi2 Pro (to order), 5" touchscreen (to order), MCP4922 + VU meters (to order).