In addition to your portable studio, you also need a master recorder. This is the machine you will make your final "release mix" on.
Connect the L and R outputs on your studio mixer or portable studio to the L and R inputs on your master recorder.
Your master recorder can be:
I use my dual CD deck to make a CD master, and also use a dual cassette deck to make a cassette master if needed. Then I use each dual deck to make copies of its master.
So why the need to make a master? Why can't the tape in the portable studio be used as it is?
Making a master is producing a final stereo tape that will play on anybody's machine. Remember that most multitrack tapes can't be played on regular home equipment, because:
So you have to COPY your tape to a machine that can make tapes that home equipment can use. In the process, you also get to create the most pleasing stereo mix from the multiple tracks you have now. This is nice, because you can twiddle with the levels and pans long after the musicians have finished playing. They can be off playing Tackle Pinochle somewhere while you are mixing down.
And if, a month from now, you don't like your mixdown (that guitar is too loud, or the horn belongs on the right), you can build a new one from that precious multitrack tape, if you thoughtfully squirreled it away for later.
There are actually several phases of making a recording:
They need to be done in the correct order.
Why do we use multitracks instead of two track recorders? Here is a scenario of the two-track studio:
Just imagine the harried sound man trying to produce a good mix with all of the musicians playing at once, balancing out the levels with as much precision as a set of headphones can allow (I've been there):
By this time, the sound man is BALD! (And there's hair all over the floor too.)
With the multitrack, we can repair those problems, even if they all occur in the same take:
Not to mention these advantages: The musicians don't even have to be playing together to make the tape, and the same musician can play more than one instrument or part.
Now you know why we use multitracks.
Now that we have all of the parts on tape, we need to produce the final product (the alternative is to make portable studio boom boxes for everyone to listen to). Here's where you can get creative long after the musicians are gone:
The multitrack tape thus lets you postpone decisions. That gives you much more control, and the ability to UNDO by mixing down again. Do I ever need that!
So why don't they include the master recorder deck in the works of many portable studios?
They wouldn't know what to include. I have mastered to cassettes, half-track and quarter-track reel to reel, CDs, video tape, and even 78 RPM records. You get your choice this way.
Link: Mixing your own sound