I've always failed to independently mix and master my tracks. I've no problems with composing but my mixing and mastering always lets me down and makes me give up finishing my tracks. My unfinished and unmastered track:
ēther
If there's one thing I've learned, especially on Audiotool, is that the snares and clap are quite loud and should be turned down some to keep them in line with the kick. I've learned this especially in house music, as just slapping some claps and snares in there and not turning them down you'll notice the kick immediately gets drowned out which is NOT good. So I suggest keeping those claps and snares at a lower level and of course check how loud they are using the VU meters on the centroid, and of course your ears.
One trick I've found to avoid claps and snares (or other sounds with very sharp attack transients) is to use envelopes to soften the attack. For example, on the Machiniste you can set the Envelope Ratio to a very small value to soften the sample attack. This way you can avoid the possibility of clipping without sacrificing volume.
Eqing is also a very important part of this. There might be an unnecessary frequency that is throwing off the mix, so you can cut or reduce it with a graphical eq. A lot of people (including myself) have the mistake of making the mix too thin to sound professional or something, and thats also bad
So if I had 2 centroids, 1 being drums and the other being synths, linked to a minimixer, I would mix all the channels in the centroids to not clip, and then bring down the level of those centroids until they don't clip, and then bring down the level of the minimixer so it's not clipping.
The main goal of mastering is to get your track as loud as possible without unpleasantness (clipping, muddiness, basically any bad sounding error in the mix).
Clipping is when an audio signal attempts to put out a current beyond the maximum capability, (In music, this maximum capability is specifically 0dB.) resulting in unpleasant amplification of the sound.
When you are mastering a track, you are mainly focusing on getting it as loud as possible, without resulting in that amplification, so we would like to peak the master at this 0dB. (The limiter does this, but we will return to that later.) The audiotool's compressor is not as efficient and useful as we would like it to be, but there is still a Peak option. On the compressor, we would like the threshold all the way up, along with the ratio. We will use this peak setting (instead of RMS.) Here is where things get kind of "mess with it until it's how you want it" and also complicated.
From using FabFilter Pro L (a mastering plugin for other DAWs) I think that the longer the attack is, the louder. Also, the shorter the release is, the louder it is. [[[ I may be incorrect, so correct me if I'm wrong ]]] (I haven't really used it in a while so I'm just going by memory.) But where the main focus is, is the gain knob. Turn it up until it's loud but not amplifying the sound. Also, on the master output, you would like the master volume all the way up, and of course the limiter on. This should keep all the sounds at 0dB and not tipping over to result in the amplification.
If you're going to push the mix loud, don't overdo it. You don't want it to be distorted, or unlistenably compressed. That's all I can say, because I don't know much other than that.
If there's one thing I've learned, especially on Audiotool, is that the snares and clap are quite loud and should be turned down some to keep them in line with the kick. I've learned this especially in house music, as just slapping some claps and snares in there and not turning them down you'll notice the kick immediately gets drowned out which is NOT good. So I suggest keeping those claps and snares at a lower level and of course check how loud they are using the VU meters on the centroid, and of course your ears.