Delay
Canonical Definition
Delay is a time shift applied to a signal so its waveform occurs later without intentionally changing its shape. An ideal pure delay has constant time offset and a phase shift that is proportional to frequency.
Distance To Time
At approximately 20°C, the speed of sound in air is about 343 metres per second, or about 13,500 inches per second.
Delay (ms) = distance difference (m) / 343 × 1000
Delay (ms) ≈ distance difference (in) / 13.5
Distance difference (in) ≈ delay (ms) × 13.5| Distance difference | Approximate delay |
|---|---|
| 1 inch | 0.074 ms |
| 6 inches | 0.44 ms |
| 12 inches | 0.89 ms |
| 24 inches | 1.78 ms |
| 36 inches | 2.67 ms |
Temperature changes the speed of sound slightly. For ordinary vehicle setup the table is a useful starting point; record temperature when tighter laboratory precision matters.
Which Channel Gets Delayed?
The earlier channel waits. If the left tweeter arrives 1.4 ms before the right tweeter at the chosen reference position, add approximately 1.4 ms to the left tweeter as the starting correction.
Some interfaces display delay directly; others display equivalent distance or distance compensation. Confirm whether a larger value means more delay or a farther virtual distance.
Pure Delay Versus Phase
A delay does not invert the waveform. It shifts the waveform later. The corresponding phase angle depends on frequency:
Phase shift (degrees) = -360 × frequency (Hz) × delay (s)A 1 ms delay is -36 degrees at 100 Hz, -360 degrees at 1 kHz, and -3600 degrees at 10 kHz. The same time shift therefore appears as different wrapped phase angles across the spectrum.
Delay, Latency, And Group Delay
| Term | Meaning | Typical use |
|---|---|---|
| Channel delay | Intentional relative time shift | Speaker and channel alignment |
| System latency | Total transport, buffering, conversion, and processing time | System synchronization and lip sync |
| Propagation delay | Travel time through air or a medium | Distance and microphone timing |
| Group delay | Frequency-dependent timing derived from phase slope | Filters, resonances, and excess delay |
DSP Resolution
Digital delay is commonly quantized to samples or fractions of samples. At 48 kHz, one sample is:
1 / 48,000 s = 20.83 microseconds
Equivalent distance ≈ 0.281 inchA product may expose coarser user-interface steps even if its internal implementation supports finer timing. Precision is useful, but measurement repeatability, acoustic center, microphone placement, and crossover phase usually dominate before the last tiny delay increment does.
Why Tape Distance Is A Starting Point
Physical distance does not include every timing effect:
- driver and enclosure phase response
- horn, waveguide, or loading depth
- crossover-filter phase
- DSP and interface latency differences
- frequency-dependent acoustic center
- reflections and cabin geometry
Use the tape value to get close, then verify the actual goal: stereo image, adjacent-driver crossover sum, or subwoofer integration.
Measurement Rules
- Define the listening or microphone reference position.
- Use a common wired or acoustic timing reference for compared traces.
- Measure one channel or driver at a time before measuring sums.
- Record crossover, polarity, level, delay, smoothing, and window settings.
- Verify the final relationship through the intended frequency band.