OK, that could be inferred from step 10 under the operating manual instructions, except you tell it to go to "aud" instead of anything else. Not very clear instructions at all and no mention of Global Volume Lock or otherwise. Thanks for the tip space2kk
. What a horrible "Manual" (I checked the French instructions to see if they were any better, but they are not). The "except Audio" remark in this section would also tend to throw someone off the scent. Here's the link to the (pdf) manual.