Thank you Pasi,
pasi wrote:If you measure the headphone output, the hf noise is probably the modulator noise, which is not audible in headphones. For line output you should use an additional low-pass filter.
I did it, that's ok.
pasi wrote:The actual output level of audio in RT-midi mode depends on channel and master volumes, note velocity, the frequency and number of notes, and also the instrument. You should be able to increase the output volume using the appropriate MIDI messages.
This is true, but even at max level, max velocity and with a 'strong' instrument (Percussion Organ), single note, I have only 0.6Vpp. I inserted a filtered preamp, so now it is ok.
pasi wrote:When you connect between Left and Right outputs, what you get out is the difference of the channels. In SCI_MODE there is a bit SM_DIFF, which inverts the other output channel. So, for mono signal you get double the voltage difference between L and R compared to between L/R and GBUF.
This does not comply with my measurement; according to my (old) oscilloscope, the L & R output are normally in phase, so a summing amplifier should double the output.
Anyway, this is not anymore relevant since I fixed the output level and I can use only one of the two outputs.
Question: in MIDI mode the two outputs are in reality two mono identical signals, right ?