The Master Reference of Audio Metering

Audio metering serves two distinct masters: Psychoacoustics (how loud the human ear perceives sound) and Electrical Limits (how much voltage the equipment can handle). No single meter can do both perfectly.

This document compiles the ballistics, scales, visual ergonomics, and technical implementations of the world’s major audio metering standards.

I. Metering Standards & Philosophies

1. The Averaging Meters (Loudness)

Designed to mimic the sluggish response of the human ear and display average energy.

• Standard VU (Volume Unit)
  • Source: ANSI C16.5-1942 / IEC 60268-17.
  • Philosophy: Deliberately ignores fast transients to approximate “perceived loudness.”
  • Scale: -20 to +3 VU (Red zone typically starts at 0).
  • Reference Level:0 VU = +4 dBu (1.228 Volts) for professional equipment.
  • Ballistics (Attack):300 ms (Time to reach 99% deflection of a steady signal).
  • Ballistics (Decay):300 ms.
  • Use Case: Vocal recording, mixing, analog tape saturation.
  • Crucial Note: Requires a “Lead” (Headroom) of 6–10 dB. If the meter reads 0 VU, the invisible electrical peaks are likely hitting +10 dBu.
• RMS (Root Mean Square)
  • Source: Mathematical derivation.
  • Philosophy: Pure mathematical calculation of average power over a time window.
  • Ballistics: Variable (dependent on software windowing).
  • Use Case: DAW signal processing, noise floor measurement.

2. The Protection Meters (Quasi-Peak)

Designed with fast attack times to protect transmitters, vinyl cutting heads, and magnetic tape from saturation.

• PPM Type I (DIN / Nordic)
  • Source: DIN 45406 / IEC 60268-10 Type I.
  • Philosophy: Catches peaks to prevent overload, but ignores ultra-short (inaudible) clicks (< 5ms).
  • Ballistics (Attack):10 ms.
  • Ballistics (Decay):1.5 seconds (for a 20 dB drop). Fast fallback.
  • Use Case: German/Scandinavian Broadcasting, Disc Cutting.
• PPM Type II (BBC / EBU)
  • Source: BS 4297 / IEC 60268-10 Type II.
  • Philosophy: Same peak detection as Type I, but with a slow decay to reduce operator eye fatigue and allow easier reading of peaks.
  • Ballistics (Attack):10 ms.
  • Ballistics (Decay):2.8 seconds (for a 24 dB drop). Slow fallback.
  • Use Case: UK Broadcasting, EBU program exchange.

3. The Digital Meters (Absolute & Semantic)

Designed for the hard ceiling of digital audio and modern streaming consistency.

• Digital True Peak (dBTP)
  • Source: ITU-R BS.1770 / EBU R128.
  • Philosophy: The “God View.” Uses 4x Oversampling to detect Inter-Sample Peaks (ISPs) that occur between samples and cause DAC clipping.
  • Scale: 0 dBTP (Max) down to -∞.
  • Ballistics:Instantaneous Attack + Peak Hold Decay.
  • Use Case: Mandatory for Netflix, HDTV, and streaming delivery to prevent codec distortion.
• Loudness (LUFS / LKFS)
  • Source: ITU-R BS.1770-4.
  • Philosophy: Uses K-Weighting (EQ) and Gating (ignoring silence) to calculate perceived loudness over the entire program duration.
  • Ballistics:
    • Momentary: 400 ms sliding window.
    • Short-Term: 3 second sliding window.
    • Integrated: Infinite average (Start to Stop).
  • Use Case: Broadcast compliance (CALM Act), Streaming Normalization.

II. Hardware Scale Markings & Varieties (PPM)

Specific scale options found on hardware meters (e.g., Ward-Beck M433/M434, Sifam).

Option	Name / Region	Visual Range	Reference Point	Distinctive Features
1	Standard BBC	1 to 7	Mark ‘4’	Complies with BS4297. White numbers on black. Standard issue for UK/Commonwealth.
2	ABC – West	-20 to +4	-8 (‘R’)	Includes a yellow marker from 0 to +6. Ref marked ‘R’.
3	ABC – East	-20 to +4	-8	Identical range to Scale 2 but lacks the ‘R’ marking and yellow marker.
4	CBC (Canada)	-4 to +20	+8	Marked “dBm 600 Ω“; includes a yellow marker from +16 to +24.
5	dBu Scale	-8 to +16	+4 (‘REF’)	Marked “dBu“; includes a yellow marker from +12 to +20.
6	Center Zero	-12 to +12	0	Simple symmetrical scale centered on 0 dB.
7	Test Scale A	-12 to +12	0	Marked “TEST” above the zero.
8	Test Scale B	-20 to +4	-8	Marked “TEST“; includes a yellow marker from 0 to +6.

III. Ballistics & Timing Reference Table

A comparative list of how fast the meters react to sound.

Meter Type	Attack (Integration)	Decay (Fallback)	Why?
VU Meter	300 ms	300 ms	Slow movement averages out peaks to show “body” and loudness.
PPM Type I	10 ms	1.5 sec (-20dB)	Fast recovery for dynamic observation.
PPM Type II	10 ms	2.8 sec (-24dB)	Slow recovery allows the eye to register the peak value easily.
True Peak	Instant (< 1 sample)	Peak Hold	Needed to capture digital overshoots invisible to other meters.
Dorrough	600 ms (Avg) + Fast (Peak)	Dual	Shows “Crest Factor” (gap between Peak and Avg) to visualize density.

IV. The Physics of “Doubling”

Rules of thumb for level changes (Source: Sengpiel Audio / Robjohns).

1. Doubling Power (Watts/Intensity)
   • Result:+3 dB
   • Context: Two loudspeakers playing the same uncorrelated signal; doubling amplifier wattage.
2. Doubling Voltage (Field Strength/Pressure)
   • Result:+6 dB
   • Context: Doubling the voltage on a wire; Doubling Sound Pressure Level (SPL).
3. Doubling Loudness (Psychoacoustics)
   • Result:~+10 dB
   • Context: The subjective human perception of “twice as loud” generally requires a 10 dB increase in level.

V. Special Visual Meters

1. The Dorrough (Relationship Meter)

• Visual: Curved LED array.
• Function: Displays Average (Persistence) and Peak simultaneously.
• Concept: The gap between the two LEDs is the dynamic range. If the LEDs are far apart, the sound is punchy. If they are close together, the sound is compressed.

2. The Single Stereo Display (SSD)

• Visual: Single row of Bi-Color LEDs.
• Function: Displays Level, Stereo Width, and Phase.
• Color Code:
  • Yellow: Mono (L+R are equal).
  • Red / Green: L or R dominance.
  • Flickering edges: Wide stereo image.

VI. Visual Ergonomics & Color Codes

Audio metering colors are rarely decorative; they are strictly functional, designed to alert the operator to Safe Levels, Warning Zones, or Stereo Phase information.

1. The Classic “Buff” (Cream) Aesthetic

The signature look of vintage Hi-Fi and the original Broadcast Standard.

• Origin: Conceived by John Miller (Weston Instruments) in 1938.
• The Logic: Early meters used high-contrast black-on-white scales. Broadcasters complained this caused “rampant operator eye fatigue” during long shifts.
• The Solution: Miller specified a “Buff” (Cream/Beige) background in the official standard. This provides strong contrast for the black needle but is softer on the eye than stark white.
• Illumination: Traditionally lit by incandescent bulbs (e.g., No. 47 frosted lamps), giving the meter a warm, “glowing” look that distinctively pops in low-light studios.
• Modern Legacy: This aesthetic is now associated with “Premium” and “High-End” audio (e.g., Luxman M10 Mk II, Reservoir watches) to evoke the nostalgia of the 1960s/70s.

Color Palette for Reproduction

If recreating this vintage aesthetic digitally, these are the target values:

Element	Hex Code	Visual Description
Dial Face (Day)	#F5E6C4	“Weston Buff.” A crisp, pale almond. Matte finish, low glare.
Dial Face (Aged)	#E8D5A8	“Vintage.” Slightly darkened by time and heat (Luxman style).
Dial Face (Lit)	#FFC680	“Tungsten.” The warm, golden amber color of the dial when backlit by incandescent bulbs.
The Needle	#1A1A1A	“Matte Charcoal.” Never pure black (which looks plastic).
Danger Zone	#CC3333	“Signal Red.” A flat, non-fluorescent red paint.

2. The “Traffic Light” Logic (LED & Bar Graphs)

Used in Dorrough, DIN, and modern Digital Meters.

• Green (Safe / Operating Range):
  • Represents the normal noise floor up to the reference level.
  • Dorrough Spec: The first 26 LEDs are green.
• Yellow (Caution / Reference / Density):
  • In Level Meters: Indicates the “Transition Zone” between safe levels and clipping.
  • Dorrough Spec: 3 Yellow LEDs follow the green section specifically to mark the Reference Level (0 VU).
• Red (Danger / Overload):
  • Indicates headroom is exhausted.
  • Standard VU: The arc from 0 to +3 VU is always printed in Red (or distinct from the black scale) to indicate overvoltage.

3. Stereo & Phase Color Standards

Used to differentiate Left, Right, and Center channels instantly.

• Red = Left Channel: “Red” and “Port” (Left) are maritime standards; also “Red” has fewer letters than “Green” or “Right”.
• Green = Right Channel: UK/BBC Twin Needle meters use a Red needle for Left and a Green needle for Right.
• Yellow / White = Sum (Mono): When a separate needle displays the Sum (M), it is often White or Yellow.

4. High-Contrast Ergonomics (The BBC Look)

Why are British meters backward?

• Style: White characters on a Matte Black background.
• Purpose: Reduced eye strain in darkened broadcast control rooms.
• Needle: Usually White (for mono) or Red/Green (for stereo) to pop against the black face.
• Contrast: Unlike the commercial VU (black ink on eggshell paper), the BBC/PPM scale is designed to minimize reflected glare from studio lights.

VII. Technical Implementation Notes

Derived from the Weston/Berliner engineering notes.

1. The Impedance Rule (Crucial for Accuracy)

A VU meter is not just a voltmeter; it is a specific circuit load.

• Internal Impedance:3,900 $\Omega$ (3k9).
• Series Resistor: A standard VU meter must be used with a 3,600 $\Omega$ (3k6) resistor in series.
• The Math: $3600 \Omega$ (Resistor) + $300 \Omega$ (Line Source) = $3900 \Omega$.
• Why? The meter must “see” its own impedance to provide accurate ballistics and frequency response. Without this matching, it is just a “dancing needle,” not a measurement instrument.

2. Frequency Response (“The Flunk Test”)

• The Vintage Roll-off: Genuine vintage VU meters often rolled off frequencies above 10 kHz (which didn’t matter for AM radio).
• The Modern Flaw: Many cheap modern “VU-style” meters are flat to 100 kHz but lack the physical damping (ballistics) to ignore peaks, making them frantic and inaccurate for loudness monitoring.

VIII. Anatomy of the Needle (Pointer Styles)

The shape of the needle is not merely aesthetic; it dictates the mass, speed, and readability of the meter.

Style	Description	Visual Characteristics	Best Use
The Spade (Lance)	The classic vintage pointer.	“Heart-Shaped” / “Teardrop”. Features a wide, spade-like body that tapers to a fine point. Often includes a visible circular counterbalance tail.	VU Meters (Weston 30). The wide body allows the eye to track the “weight” and momentum of the audio.
The Knife-Edge	The scientific instrument pointer.	Razor Thin. A very thin, flat blade turned on its edge (or painted as a fine line) to eliminate parallax error.	PPMs (BBC/Sifam). Critical for reading exact values (e.g., verifying a “Mark 6” peak).
The Baton	The industrial indicator.	Rectangular Bar. A straight line with uniform width, blunt or squared-off at the tip.	Consumer / Industrial. High visibility at a distance, but lower precision.
The Hollow Diamond	The Hi-Fi luxury pointer.	Skeletonized. A diamond or spade shape with the center cut out.	High-End Audio. Reduces moving mass to improve transient response while maintaining visual “size.”