Bowie,
by channels, are you referring to noise channels?
If so, i just auto noise it per the owner's manual before detecting at a site and call it a day.
But i think you're referring to the 3 sensitivity channels.
The only user control once in manual sens., is the setting you punch in which sets all 3 channels equal to that setting. In other words, individual channels cannot be set differently in manual sens.
In AUTO, those 3 channels are typically averaged down to a single 'lower' sensitivity level based on soil conditions, EMI, etc for a more stable/accurate ID but at the expense of detecting deeper targets. AUTO is great for sites that have relatively shallow targets down to around 8 inches or so. For me around here with the over hunted parks over the last few decades, the only remaining oldies are usually deep which is why i use manual sens..
The manual setting is typically determined by the number of falsing encounters, soil, nearby EMI, junk densities and/or the users ability to cope with unending squeaks and squawks.
Like olives (and sushi
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), the unending squeaks and squawks are an acquired taste! LOL! But if persevered, very rewarding for finding those deep oldies others walk over!
Rule of thumb...the higher the manual sensitivity setting one can tolerate, the deeper seeking the eTRAC will be, squeaks, squawks or not.