Feedback from the Ardour to the the control surface is very useful for a number of things. Motor faders need to know where the the track they have been attached to is at before they were assigned otherwise the DAW fader will jump to where the controller fader is. Likewise, the buttons on each strip need to know what their value is so they can light their LED correctly. Transport controls should let you know if they are active too. This is what feedback is all about.
Ardour does feedback by sending the same path back that is used to control the same function. As such any controls that have feedback have a parameter that is the value of the control or it's state (on or off). In the case of OSC paths listed on the main OSC page as having no parameter, if they have feedback, they will also work with a 1 for button press and 0 for button release. This is because many OSC controllers will only use exactly the same path for feedback as for control. For example:
can be used also in the form:
|/transport_stop press||where press is an int/bool indicating if the button is pressed or not.|
The feedback does not have the same meaning as the control message. Where the button release sent to Ardour will be ignored and has no meaning. Both states have meaning in feedback to the controller. The feedback will be:
|/transport_stop state||where state is an int/bool indicating if the transport is stopped or not.|
With feedback turned on, OSC control commands that try to change a control that does not exist will get feedback that resets that control to off. For example, sending a /strip/recenable to a buss will not work and Ardour will try to turn the controller LED off in that case. Also note that Pan operation may be limited by pan width in some cases. That is with pan width at 100% (or -100%) there is no pan position movement available.
It may come as a surprise, but feedback often generates more network traffic than control itself does. Some things are more obvious like head position or meters. But even a simple button push like transport start sends not only a signal to turn on the play LED, but also one to turn off the stop LED, the Rewind LED, the Fast Forward LED and the Loop LED. That is still minor, think instead of a surface refresh such as happens when the surface is first connected and then most of that happens every time the fader strips are banked. This is why feedback is enabled in sections so that as little feedback as is actually needed is sent. This is also a consideration if the surface is connected via wifi.
List of OSC feedback messages
These messages are feedback only. They are sent as status from Ardour and some of them may be enabled separately from other feedback. See: Calculating Feedback and Strip-types Values.
See strip section below for info about ssid and wrapping it into the path. Also /master and /monitor support what the /strip does.
In the case where Gainmode is set to position, the track name will show the dB value while values are changing.
|/strip/name ssid track_name||where track_name is a string representing the name of the track|
|/session_name session_name||where session_name is a string representing the name of the session|
|/strip/meter ssid meter||where meter is a value repesenting the current audio level. (the exact math used is determined by the feedback bits set)|
|/strip/signal ssid signal||where signal is a float indicating the instantaneous audio level is -40dB or higher.|
|/position/smpte time||where time is a string with the current play head time. Seconds as per smpte.|
|/position/bbt beat||where beat is a string with the current play head bar/beat.|
|/position/time time||where time is a string with the current play head time. Seconds are in milliseconds|
|/position/samples samples||where samples is a string with the current play head position in samples.|
|/heartbeat LED||where LED is a float that cycles 1/0 at 1 second intervals.|
|/record_tally state||Some record enable is true or "ready to record". For a "Recording" sign at studio door.|
|/transport_stop state||state is true when transport is stopped|
|/transport_play state||state is true when transport speed is 1.0|
|/ffwd state||state is true when transport is moving forward but not at speed 1.0|
|/rewind state||state is true when transport speed is less than 0.0|
|/loop_toggle state||state is true when loop mode is true|
|/cancel_all_solos state||Where state true indicates there are active solos that can be canceled.|
|/rec_enable_toggle state||Master record enabled.|
Master and monitor strips
Master and monitor strips are similar to track strips but do not use the SSID. Rather they use their name as part of the path:
|/master/gain dB||where dB is a float ranging from -193 to +6 representing the actual gain of master in dB|
|/master/fader position||where position is an int ranging from 0 to 1023 representing the fader control position|
|/master/trimdB dB||where dB is a float ranging from -20 to +20 representing the actual trim for master in dB|
|/master/pan_stereo_position position||where position is a float ranging from 0 to 1 representing the actual pan position for master|
|/master/mute state||where state is a bool/int representing the actual mute state of the Master strip|
|/monitor/gain dB||where dB is a float ranging from -193 to 6 representing the actual gain of monitor in dB|
|/monitor/fader position||where position is an int ranging from 0 to 1023 representing the fader control position|
|/monitor/mute state||where state is a bool/int representing the actual mute state of the Monitor strip|
|/monitor/dim state||where state is a bool/int representing the actual dim state of the Monitor strip|
|/monitor/mono state||where state is a bool/int representing the actual mono state of the Monitor strip|
Track specific operations
For each of the following, ssid is the surface strip ID for the track
Some Surfaces (many Android applets) are not able to deal with more than one parameter in a command. However, the two parameter commands below can also be sent as /strip/command/ssid param. Feedback can be set to match this with the /set_surface/feedback state command. See Calculating Feedback and Strip-types Values.
|/bank_up LED||where LED is a bool that indicates another bank_up operation is possible.|
|/bank_down LED||where LED is a bool that indicates another bank_down operation is possible.|
|/strip/name ssid track_name||where track_name is a string representing the name of the track (note there is no coresponding command to set the track name)|
|/strip/mute ssid mute_st||where mute_st is a bool/int representing the actual mute state of the track|
|/strip/solo ssid solo_st||where solo_st is a bool/int representing the actual solo state of the track|
|/strip/monitor_input ssid monitor_st||where monitor_st is a bool/int. True/1 meaning the track is force to monitor input|
|/strip/monitor_disk ssid monitor_st||where monitor_st is a bool/int. True/1 meaning the track is force to monitor disk, where both disk and input are false/0, auto monitoring is used.|
|/strip/recenable ssid rec_st||where rec_st is a bool/int representing the actual rec state of the track|
|/strip/record_safe ssid rec_st||where rec_st is a bool/int representing the actual record safe state of the track|
|/strip/gain ssid gain||where gain is a float ranging from -193 to 6 representing the actual gain of the track in dB.|
|/strip/fader ssid position||where position is an float ranging from 0 to 1 representing the actual fader position of the track.|
|/strip/trimdB ssid trim_db||where trim_db is a float ranging from -20 to 20 representing the actual trim of the track in dB.|
|/strip/pan_stereo_position ssid position||where position is a float ranging from 0 to 1 representing the actual pan position of the track|
Selection feedback is the same as for strips, only the path changes from /strip to /select and there is no ssid. there are some extra feedback and commands that will be listed here.
|/select/n_inputs number||where number number of inputs for this strip|
|/select/n_outputs number||where number number of outputs for this strip|
|/select/comment text||where text is the strip comment|
|/select/solo_iso state||where state is a bool/int representing the Actual solo isolate state of the track|
|/select/solo_safe state||where state is a bool/int representing the actual solo safe/lock state of the track|
|/select/polarity invert||where invert is a bool/int representing the actual polarity of the track|
|/select/pan_stereo_width width||where width is a float ranging from 0 to 1 representing the actual pan width of the track|
|/select/send_gain", sendid send_gain||where sendid = nth_send, send_gainis a float ranging from -193 to +6 representing the actual gain in dB for the send|
|/select/send_fader", sendid send_gain||where sendid = nth_send, send_gainis a float ranging from 0 to 1 representing the actual position for the send as a fader|
|/select/send_name sendid send_name||where send_name is a string representing the name of the buss this send goes to.|
Every single menu item in Ardour's GUI is accessible via OSC. However, there is no provision for returning the state of anything set this way. This is not a bad thing as most menu items either do not have an on/off state or that state is quite visible. Bindings that affect other parameters that OSC does track will show on those OSC controls. Examples of this might be track record enable for tracks 1 to 32, play or stop.