  Timbre is a primary mode of expression in diverse musical contexts. However,
prevalent audio-driven synthesis methods predominantly rely on pitch and
loudness envelopes, effectively flattening timbral expression from the input.
Our approach draws on the concept of timbre analogies and investigates how
timbral expression from an input signal can be mapped onto controls for a
synthesizer. Leveraging differentiable digital signal processing, our method
facilitates direct optimization of synthesizer parameters through a novel
feature difference loss. This loss function, designed to learn relative timbral
differences between musical events, prioritizes the subtleties of graded timbre
modulations within phrases, allowing for meaningful translations in a timbre
space. Using snare drum performances as a case study, where timbral expression
is central, we demonstrate real-time timbre remapping from acoustic snare drums
to a differentiable synthesizer modeled after the Roland TR-808.
