Sharon, here is some additional info which might help;
The term subtone refers to the technique of playing with soft tone on slow songs and is a technique used mainly in the lower register.
I do not know when this technique was developed but it was very popular in the big band era and remained popular in the 50s and 60s, especially on the slow Top 40 hits. And you will still hear it today in many forms of sax music.
A few suggestions to get started;
1. Assuming that all of the pads are leak proof, play a low G.
2. Bring the lower lip back over the bottom teeth so that more upper skin below the lip line area is pressing gently against the reed. Depending on the width and thickness of your lip, you may need more, or less, of the skin below the lip line against the reed. If you have a wide lower lip, this can work to your benefit. If you have a thin lower lip, more meat on the reed from the area below the lip line may be needed for a cushion.
6. Now G to F to E and so on.
8. Repeat this over and over. G to F to E to D to low C holding and maintaining a soft whisper tone.
9. Once you begin to get good control of it, you can adjust the volume, corners of the mouth, amount of lip in the mouth, amount of air/tone mix, etc. to develop your own subtone quality.
This is, by no means, the only way to approach the subtone but maybe it will help you get started. It is a technique that is well worth learning.
A link for the subtone;
http://www.petethomas.co.uk/saxophone-subtone.html