First time you load Aeolus there is no sound

[riban-bw]

Describe the bug Loading some synth engines for the first time will not produce any sound output. This includes Aeolus.

To Reproduce Steps to reproduce the behaviour:

1. Clean All
2. Add new Synth - Aeolus, Meantone 1/4, Bank 01, Preset 01
3. Send MIDI note-on, e.g. play a connected MIDI keyboard

Expected behaviour Audio appears on the output.

Actual behaviour MIDI indication shows but no audio appears on the output.

Setup:

• HARDWARE Raspberry Pi 4 Model B Rev 1.4 Audio: ZynADAC Display: ZynScreen 3.5 (v1) Wiring: MCP23017_ZynScreen I2C: MCP23017@0x20, MCP23017@0x21, ADS1115@0x48, MCP4728@0x60
• SYSTEM Raspbian GNU/Linux 10 (buster) Build Date: 2020-09-05 Memory: 9% (176M/1872M) SD Card: 73% (20G/29G) Temperature: 54.0ºC Overclock: None
• MIDI Profile: default.sh Tuning: 440 Hz Receive Mode: Stage (Omni On) ZS3 Sub-SnapShots: On MIDI to Output: Off Master Channel: 16
• SOFTWARE zyncoder: testing (172e160) zynthian-ui: testing (81d8236) zynthian-sys: testing (af767d2) zynthian-data: testing (10e1f9f) zynthian-webconf: testing (1d5e287)

Additional context Aeolus GUI shows with the correct preset configured. ZynMidiRouter outputs 1-4 are connected to Aeolus Midi_in. Aeolus audio output is connected to mixer channel 4. MIDI inputs are connected to ZynMidiRouter dev inputs.

Pressing the "Recall" button on the Aeolus interface starts sound working.

Log shows:

May 17 06:11:22 zynthian1 startx[488]: WARNING:zynthian_engine.proc_get_output: Command Prompt is not defined!

Sometimes it works (maybe if loaded but not played for a while).

[riban-bw]

This is working in the audio player branch so I will close this issue.