Sorry if this might seem ignorant, but would it be an idea to make [lop], [hip] and so on objects for convenience sake to come with the distribution that would go alongside the names the audio objects? This might only be me being used to the supercollider syntax of adding a .ar (for audio, or ~) or .kr (for control, float) after the object/class name.
i don't think, it is feasible to write straight-forward objects for message filtering ...
pd has no notion of control rate, as supercollider or csound have ... messages can be used to emulate control rate signals, however there is no guarantee that control rate events occur monotonic, nor a way to figure out its sampling rate
by downsampling subpatches you can probably get close to the semantics of control-rate in other systems, although it might lack some expressive power
best, tim