Your perception of the loudness of an audio track depends on several factors. One is the absolute loudness, another is the dynamic range, a third is the kind of material.
The maximum signal you can record on a digital system is fixed by the number of bits available. If an analogue system is overdriven, the result is a gradual increase in distortion; digitally, saturation is a wall and even a slight step beyond it is highly disturbing. (There are, of course, some kinds of 'music' which are designed to be distorted; I have nothing to contribute for them.) So the maximum level you want to set is something which does not go beyond maximum loudness.
The second factor is dynamic range - the range from the loudest to the quietest passage in the program. At a symphonic concert, that can be as high as about 100 db - for a very quiet audience and some very loud passages. CD recording at 16 bits offers 96 db range. A very good tape deck can deliver about 60 db. But in many environments, use of wide dynamic range is undesirable, so the actual dynamic range on a recording may be compressed to 40 db or less. Different recordings will vary in the amount of compression used - and the average sound level depends more on that than on the absolute maximum you have to keep to 100% (16 bits).
The third factor is the program content. I don't know about you, but I want a march to sound louder than a lullaby. So even after you set the maximum and mean levels by normalizing and compressing, you have to consider how loud you want the result to be.
All is not as bad as this sounds. In general, a given label will be pretty consistent across its recordings of a single group or even of a single kind of music. But as you try to mix a greater variety, you face the problem that the software doesn't know what compression makes sense (or how best to implement it) - and it certainly does not determine how loud you want a given track to seem on a given compilation. The automatic level setters do what they can, but they are basically limited to setting the maximum level. The rest must be done to your taste by you. A good WAV editor, such as CoolEdit Pro will let you shape the compression on a track-by-track basis as well as permitting you to adjust level and keep from hitting saturation. It will also denoise, alter channel and frequency balance, and do many wonders - with a lot of time and effort on your part. To avoid that, choose the tracks for your compilation with some care and take what you get with automatic balancing.
E-mail me at cdrecording@mrichter.com
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