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Add and control effects from a script

Goal: put an effect on a track (or the master), find its parameters, set one, bypass it, and — when a built-in isn't enough — host a VST3/LV2 plugin effect. All over the gRPC lane, so it scripts and repeats.

Effects live in a mixer insert's chain, addressed by a (insert, slot) pair:

  • Insert is a mixer strip. Insert 0 is the master; each track has its own insert (its strip carries the track's name).
  • Slot is the position in that insert's effect chain — add_effect returns the slot it landed in.

Find the insert for a track

add_synth_track gives you a track id; effects attach to that track's insert. List the inserts and match by name (or just target the master, insert 0):

from gloopy import Gloopy

with Gloopy() as g:
    lead = g.add_synth_track("Lead", wave="SAW")
    insert = next(i["index"] for i in g.list_inserts() if i["name"] == "Lead")

(let* ((lead   (add-synth-track "Lead" :wave :saw))
       (insert (getf (find "Lead" (list-inserts)
                            :key (lambda (i) (getf i :name)) :test #'string=)
                     :index)))
  …)

Add an effect and set a parameter

Add a built-in reverb, ask what parameters it exposes, then turn the wet level up. Every effect reports its parameters (with ranges) — don't guess, query:

ins, slot = g.add_effect(insert, "REVERB")
print(g.effect_params(ins, slot))
# [{'name': 'Room', 'value': 0.5, 'min': 0.0, 'max': 1.0},
#  {'name': 'Damp', 'value': 0.5, ...}, {'name': 'Wet', 'value': 0.33, ...}]
g.set_effect_param(ins, slot, "Wet", 0.5)

(let ((slot (add-effect insert :reverb)))
  (effect-params insert slot)
  ;; => ((:NAME "Room" :VALUE 0.5 :MIN 0.0 :MAX 1.0) (:NAME "Damp" …) (:NAME "Wet" …))
  (set-effect-param insert slot "Wet" 0.5))

G="grpcurl -plaintext -proto proto/gloopy.proto -import-path proto"
# add reverb to insert 1 -> returns {"insert":1,"slot":0}
$G -d '{"insert":1,"type":3}' 127.0.0.1:50051 gloopy.v1.Gloopy/AddEffect
$G -d '{"insert":1,"slot":0}' 127.0.0.1:50051 gloopy.v1.Gloopy/GetEffectParams
$G -d '{"insert":1,"slot":0,"name":"Wet","value":0.5}' \
    127.0.0.1:50051 gloopy.v1.Gloopy/SetEffectParam

The built-in effect type is a name in the clients ("REVERB", :reverb) and an integer on the wire (3). The full set — gain, filter, delay, reverb, limiter, bitcrusher, compressor, EQ, waveshaper, and more — is listed under Effect. (In Lisp, the keyword shorthands cover :gain :filter :delay :reverb; pass the integer for the rest.)

Setting a parameter to exactly 0

SetEffectParam goes over gRPC, and proto3 drops zero-valued fields on the wire — so you can't set a parameter to exactly 0.0 this way. Use a tiny value, or the OSC lane (fx-param), for a true zero. Same reason as the model's control-lane split.

Bypass or remove

g.set_effect_bypass(ins, slot, True)   # audition without it
g.remove_effect(ins, slot)             # take it out of the chain

(set-effect-bypass insert slot t)
(remove-effect insert slot)

Host a plugin effect

When a built-in won't do, host a VST3/LV2 effect. Find its identifier in the plugin list, then add it exactly like a built-in — it lands in a slot and its parameters come back from effect_params the same way:

fx = [p for p in g.list_plugins() if not p["is_instrument"]]
ins, slot = g.add_plugin_effect(insert, fx[0]["identifier"])

(let* ((fx (remove-if (lambda (p) (getf p :instrument)) (list-plugins)))
       (slot (add-plugin-effect insert (getf (first fx) :identifier))))
  (effect-params insert slot))

See also