The NES output pixels at NTSC and sound at sample rate. MiSTer wraps those signals through scaling, framebuffering, and HDMI encoding to land them on a modern monitor. This week you trace that path and produce a visible or audible artefact by modifying the audio mix.
Reading
- Copetti, the audio + video sections of the NES writeup; revisit with the MiSTer scaler context.
- MiSTer-devel docs, the scaler-and-audio section.
- Altice, I Am Error, the chapter on Famicom audio. Sets up why the APU choices became the sonic signature of the console.
Lecture
Roughly three hours across two sessions. Key arc:
- From PPU pixels to HDMI. Scaler, line buffer, video timing generator.
- From APU samples to stereo line-out. Mix bus, DAC, output stage.
- Why MiSTer scales rather than passes through raw NTSC. The HDMI sync constraint.
- Audio mix modification. The five-line change that adds reverb.
- Lag accumulation across the scaler. The competitive-gaming pedagogical aside.
Lab pack
Lab Pack 8 traces the HDMI output path and modifies the audio mix. See Lab Pack 8: HDMI Output Path Trace.
Classroom tools
- SPK-101 classroom: NES APU inspector. Already-shipped, drops you into the live APU channel data.
- Quartus Prime Lite for the MiSTer compile.
- iverilog plus yosys for the synthesise-then-verify loop on the academy-mirror core if you are taking the no-DE10 path.
Architecture comparison sidebar
Modern game consoles do scaling in dedicated silicon and report sub-frame latency. MiSTer does it in soft logic on a 2014 Cyclone V and the cost shows up as a frame or two of lag. The pedagogical point is that the scaler is a real subsystem with real cost, and 'free upscaling' is never free.
Reflection prompts
- How many clock cycles does the MiSTer scaler add between PPU pixel and HDMI pixel?
- If you remove the line buffer entirely and pass raw NTSC, what breaks?
- Why does MiSTer mix stereo even though the NES is mono?
What is next
Module 9 closes the analyze-not-copy loop by mapping the NES's memory-mapped I/O pattern against the SB6141 cable modem you will reverse in RE-101.