Transients are especially hard to synthesise additively because they require rapidly varying phases across many partials

A sharp attack or transient in a real instrument (piano hammer strike, guitar pluck) relies on many partials rapidly building up in a specific phase relationship. In additive synthesis the phases of individual oscillators must be precisely controlled and rapidly varied. Static phase relationships between oscillators produce no transient; the spectral envelope of the steady-state tone is easy to mimic, but the temporal onset is not. This is why additive synthesis tends to produce organ-like results: organs have no transient, just a quasi-instant onset of the steady-state harmonic spectrum. Noisy instruments (drums, flutes, cymbals) face a related problem — they require many noise-modulated partials.

Examples

A modelled piano transient in additive synthesis requires the phases of all partials to cohere on the attack millisecond, then decay independently — difficult to program without automation or resynthesis tools. A workaround: mix an impulsive noise burst with a static additive tone for a ‘fake’ transient.

Assessment

Explain why an additive synthesizer patch of a piano tends to sound more like an organ, and describe one work-around technique to restore a sense of transient attack.