NTSC SIGNAL LAB

◈ SIGNAL STRUCTURE

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

• Front Porch (~1.5µs) — Voltage stabilization
• Sync Pulse (~4.85µs) — H-sync at 0V (below black)
• Back Porch (~4.7µs) — Black level reference
• Colorburst (~2.5µs) — 8-10 cycles of 3.58MHz subcarrier
• Active Video — Luminance + modulated chrominance

⟐ SYNC & TIMEBASE

The vertical blanking interval contains a carefully designed pulse sequence:

• Pre-equalizing pulses — Half-line rate pulses that prepare the sync separator
• Long sync pulses — Inverted timing signals the V-sync integrator
• Post-equalizing pulses — Restore normal H-sync timing

The equalizing pulses maintain horizontal sync during vertical retrace and differentiate odd/even fields for interlacing.

◈ H & V HOLD

Early TV receivers used free-running oscillators for deflection. The sync separator extracts timing pulses to lock these oscillators:

• H-Hold drift — Image tears diagonally like a barber pole
• V-Hold drift — Image rolls vertically up or down
• Weak signal — Sync separator misses pulses, oscillators lose lock

Try the H-HOLD and V-HOLD knobs to see these classic artifacts!

◈ "NEVER THE SAME COLOR"

NTSC's biggest weakness: phase errors in the received signal cause hue shifts. Unlike PAL, 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 visible at color boundaries
• Rainbow — High-frequency luma creates false color
• Ringing — Gibbs overshoot at sharp edges
• Color Bleed — Chroma bandwidth much less than luma

◈ VHS & TAPE

VHS recordings add artifacts on top of NTSC:

• Head Switching — Noise bar at bottom of frame
• Tracking Noise — Horizontal distortion from misaligned tape
• Generation Loss — Each copy degrades signal