NTSC SIGNAL LAB

◈ SIGNAL STRUCTURE

Each scan line of an NTSC signal lasts ~63.5µs and contains:

• Front Porch (~1.5µs) — Voltage stabilization period
• Sync Pulse (~4.7µs) — Horizontal sync at -40 IRE
• Back Porch (~4.7µs) — Black level reference
• Colorburst (~2.5µs) — 8-10 cycles of 3.58MHz subcarrier
• Active Video — Luminance + modulated chrominance

◈ YUV COLOR SPACE

RGB signals are converted to YUV for transmission:

• Y (Luminance) — Brightness, compatible with B&W TVs
• U (B-Y) — Blue difference signal
• V (R-Y) — Red difference signal

U and V are zero in monochrome scenes, saving bandwidth.

◈ QUADRATURE MODULATION

U and V are combined onto a single 3.579545 MHz subcarrier using QAM:

• U modulates sin(ωt), V modulates cos(ωt)
• The 90° phase difference allows independent recovery
• Chrominance amplitude ≈ saturation
• Chrominance phase ≈ hue

◈ "NEVER THE SAME COLOR"

NTSC's biggest weakness: phase errors in the received signal cause hue shifts. Unlike PAL (which reverses phase each line to cancel errors), NTSC relies on the receiver's TINT knob.

Try the PHASE ERROR slider to see this infamous artifact!

◈ COMPOSITE ARTIFACTS

Because luma and chroma share the same signal, they interfere:

• Dot Crawl — Subcarrier pattern visible at color boundaries, cycling at ~15 Hz
• Rainbow (Cross-Color) — High-frequency luma patterns (stripes, text) create false color
• Ringing — Gibbs overshoot at sharp edges from bandwidth limiting
• Color Bleed — Chroma bandwidth (~0.5 MHz) is 8× less than luma (~4.2 MHz)
• Chroma Delay — Filter group delay offsets color horizontally vs brightness

◈ VHS & TAPE ARTIFACTS

VHS recordings add their own artifacts on top of NTSC:

• Head Switching — Visible noise bar at the bottom where rotary heads swap
• Chroma Under — VHS records chroma at ~629 kHz, severely limiting color bandwidth
• Tracking Noise — Horizontal distortion from misaligned tape path
• Generation Loss — Each copy degrades signal (increase noise + color bleed)