Source Playback Architecture
Canonical Definition
Source playback architecture is the ordered set of media, software, transport, control, clock, decoding, sample-rate, volume, conversion, routing, and analog stages that turn a selected program into a physical signal at the next system boundary.
The Layers
media or live source
→ app and operating-system processing
→ codec or PCM representation
→ transport and connection
→ receiver or vehicle host
→ decoding, mixing, resampling and volume
→ DSP or head-unit processing
→ DAC and analog line stage
→ next device input
→ amplifier and loudspeakerAn analog auxiliary input begins its analog path earlier. A storage device may deliver files rather than real-time audio. Smartphone projection adds a coordinated phone-and-host session. A factory system may retain control and alert stages after the visible source.
Five Questions For Every Source
- What is the content? File, stream, radio, call, prompt, alert, or generated test signal.
- Where does it become PCM? Phone, app, decoder, host, receiver, or DSP.
- Who owns level? App, operating system, projection session, head unit, factory volume group, DSP, or analog stage.
- Where does it become analog? Phone, head unit, interface, DSP, DAC, or amplifier input module.
- What can interrupt it? Calls, navigation, assistants, alerts, safety audio, reconnects, mute, or power state.
Same Song, Different System
| Mode | Possible extra boundaries |
|---|---|
| Bluetooth Classic | profile and codec negotiation, radio buffering, sink decode, call-path switch |
| Bluetooth LE Audio | LE Audio roles, services, LC3, isochronous transport, unicast or broadcast state |
| USB storage | file-system support, head-unit decoder, indexing, local DAC |
| USB Audio Class | host/device role, descriptors, clock and feedback, host mixer |
| CarPlay or Android Auto | projection session, phone and host processing, audio focus, volume groups |
| Analog auxiliary | phone or player DAC, analog volume, cable ground, input clipping |
Verification
- Use one known file or test signal across source modes.
- Record every visible and hidden processing or level state you can identify.
- Measure clean maximum level, response, noise, latency, and channel routing.
- Trigger calls, navigation, alerts, pause, resume, reconnect, key cycle, and sleep.
- Save an approved calibration state and user operating range for each source.