A question from an RP reader...
"When balancing the instrumental, at what percentage (volume) should one's bass instrument be?"
I'm guessing that by 'instrumental', he means the backing instruments of a song.
Firstly let me deal with the concept of percentage. It doesn't really work all that well for audio. For instance, consider a signal at a good, healthy, but not ear-damaging level. Reduce it by 6 dB. You can clearly notice the difference, but the level is still strong. Try another 6 dB. It seems to have gone down by a similar amount, yet is still very clearly audible. Another 6 dB. It has far from gone away yet.
But considered in percentage terms, the signal level is now down to 12.5% of what it was originally. You'd think that the signal would hardly be audible at all, but it most definitely is. A reduction in level of a total of 18 decibels corresponds very well to the way the ear perceives sound. Measuring a change in level in percentage terms isn't wrong, but it somehow doesn't match up with what we hear.
Let's try and put a figure on how loud the bass instrument ought to be. What about 50%?
In terms of decibels, what this would mean is that the bass instrument is as loud as all of the rest of the instruments playing together. So if you look at the level on a meter and you take away the bass, then the level may hover around -9 dBFS. If you take away all of the instruments except the bass, then likewise it hovers around -9 dBFS.
Interestingly, if you combine the bass and all of the rest of the band, the level will now hover somewhere around -6 dBFS. Somehow 50% plus 50% doesn't equal 100%. This is because the two signals are uncorrelated, but that isn't particularly relevant for the issue in hand.
But what would it sound like?
In this case, the bass would almost certainly be too loud, unless the bass really is the most important instrument in the song. So what is the correct percentage?
Well I'd like to move away from the idea of percentage and look at the issue in a rather different way.
Suppose you play the instruments without the bass and the meters are hovering around -9 dBFS. Now raise the bass. Lift the fader until you can just see the meters rise up from around the -9 dBFS mark. This is the point at which one instrument starts to dominate the mix. Now you have to ask yourself, do you want it to dominate, or do you want it to blend in?
You can't mix by looking at meters, but they can give you an interesting indication of the way in which different instruments contribute to the song. This 'point of dominance' is of particular relevance to vocals. Often when a vocal crosses this point, it is too loud in comparison with the instruments. It's a useful quick check when learning how to mix.
In conclusion... Well I'm sorry that I haven't really come to a conclusion. But it isn't the kind of issue where there are hard and fast rules. But thinking around the issue can be very instructive. Those who are thinking carefully about what they do when they mix will create better mixes.
By the way, the photo illustrates a track where the bass guitar is vitally important. Without the bass, this song would just be a lot of hot air!