Psychoacoustic phenomenon: the ear localizes sound by earliest signal arrival, not by volume — a delayed signal <50ms perceived as spatial width. Creative tool for surround and stereo imaging.
Haas Effect
Your ear follows the first signal — not the loudest. This is precisely where the Haas Effect comes in, and it's one of the most important psychoacoustic tricks you need in surround and stereo mixing. When an identical audio signal arrives with a delay of approximately 5 to 50 milliseconds after the original, your brain perceives both not as separate events, but as a single source — albeit spatially widened. Localization follows the earliest onset, not the loudness. This means you can create depth and width without the listener realizing you're delaying.
On set and in the mix, it works like this: If you want to make dialogue or an ambient element wider in stereo without artificially splitting it, you send the signal to a parallel channel with a 10–30ms delay. The level of this delayed signal remains low — it's not about doubling, but about subtle spatialization. In orchestral recordings, we use this phenomenon to spatially anchor individual instrument groups. A cello ensemble immediately sounds fuller when the first violas run in parallel with a 15ms delay. In surround mixing, the effect is indispensable: you place the dialogue upfront, but send it with a mini-delay to the rear channels, and the viewer is immersed — without the sync suffering.
Important: The effect no longer works with delays over 50ms — then you hear two separate events, which is called echo instead of Haas. Below 5ms, you often notice little effect because the time difference is too small. The sweet spot is between 10–40ms. Frequency dependence also counts: Haas works significantly worse at low frequencies (below 700Hz) than in the mid-range — this is important when working with bass elements. Some mixers implement Haas in combination with slight EQ differences — for example, a few dB high-pass on the delayed signal — to enhance the illusion.
Practical tip: Don't use Haas as a crutch for poor stereo recordings. It's a tool for targeted spatial design. In digital mixing, this is achieved via delay plugins or even simple sample offsets in the sample editor — millisecond accuracy is standard. Ensure your delay time is exact; a few milliseconds of error significantly alter the effect. And always: test for mono compatibility. If the delayed signal and the original add up to comb filtering effects in mono, you'll suddenly hear holes in the frequency response.