Motivation: - addressing low frequency stuttering issues heard in 714 LS renders of some HOA3 content. SBA Modes affected: - HOA2/HOA3 inputs at 256kbps and above This tuning fix includes three changes: - Covariance smoothing: additional smoothing at lower frequency bands to more closely match pre-merged SBA covariance smoothing behaviour. - Transient detection for covariance smoothing resetting: tuning of transient detector to work better with tonal signals - HP20 changes: all signals ingested by SPAR are now HPF'd at the encoder i.e. FOA + planar HOA signals where present (previously FOA only), and not at the decoder for HOA inputs.