This age-old question continues to be a stumper for many people getting in to music production.
“Why is it that when I do a mixdown to DAT and then copy the DAT mix to cassette, the playback volume level of my cassette is always lower than any store-bought cassette I have of rock music? How can I get my levels up comparable to commercially available music found on cassette? During mixdowns I always make sure the level meters on my Mackie 8-Bus console, my ADATs, as well as DAT and cassette decks, are as close to red as I can get them without going into the red and causing distortion.”
Funny how meters don’t always really tell us what something sounds like isn’t it? In a word, the answer is compression. Proper use of compression will raise the average sound level and thus raise the perceived volume of sound without making peak levels much higher. Limiting can be used to raise average volume levels without any increase in peak levels. One has to be careful though, because these processes are often accompanied by side effects that change the sound of the audio, sometimes in undesirable ways. The use of compression in music recording is literally as old as tape itself; one of the benefits of analog recording is that tape saturation provides a certain amount of compression. Besides the difference in sound between analog and digital recorders one of the aspects of digital recording that has been hard for engineers to adapt to has been Digital’s lack of this “natural” compression. Rock and pop tracks will tend to sound wimpy unless measures are taken to increase the average level.
Engineers cope with this in a variety of ways. Basically you can compress (or soft limit) your tracks before the initial A/D conversion, as a process during mixing, upon your final mix, or some combination of those. Normalization, another variation on compression, has become a very popular process to employ during mixing and/or mastering because it is a relatively easy way to substantially increase the perceived volume of your tracks without too many audible artifacts (depending upon how severe the normalization is). Making a great sounding mix, and then being able to get 3 dB to 6 dB more overall level at the end has sold many different types of digital normalization equipment in the past five years. Of course, why we strive to have so much dynamic range in digital only to compress it all out of our music is another topic for another time.
As for your final step of going from DAT to cassette, the problem is still mostly compression. First, don’t be afraid to slam the levels on the cassette. I don’t just mean slightly going into the red. I’m saying, “slam” them. Put your prerecorded tape in and look at the average levels of the meters, then look at the average levels of your recording. I’m not talking peak levels; I’m saying look at where the meters spend most of their time. Yours is probably lower. You need to compress (or normalize) until you can get a higher average level without higher peak levels (they will introduce distortion). You may find that you can’t get the average level as high as the prerecorded tape without the tape distorting. This is caused by two factors: 1) Your tape machine isn’t optimized (biased) for the type of tape you are using. Corollary to this, and possible third factor is that your tape just isn’t as good as it needs to be. 2) Your recording has too much very low and/or very high frequency information in it to easily be recorded on tape at high levels. Analog tape is not linear. It doesn’t do as well at very low or high frequencies, especially if noise reduction is being used, and especially if there are big transients with those frequencies. The solution may be as simple as rolling off some low and high frequency content, or you may have to go back to your mix and pull some of the low bass out of that kick drum track. There’s no reason, for example, to try to record much of anything above about 12 kHz on a cassette. Most cassette recorders are not going to record it very well (if at all) and it eats up a ton of headroom. If you get the proper equipment and experiment enough with these factors you will find that you’ll soon be getting 95% – 99% of the level on your tapes as the pros.