At present, there are two popular singing methods, namely "fixed singing method" (abbreviated as "fixed singing method") and "first tune singing method" (abbreviated as "first tune singing method").
"fixed roll-call method" no matter what key is sung, the roll-call of each tone remains the same. It always sings 1 (multiple) with 1 in C key and 2 (coming) with 2 in C key. When you meet the rising and falling notes on the spectrum, you can raise or lower the pitch as marked by the mark. The advantage of "fixed roll-call method" is that it is easy to remember. C, D, E, F, G, A and B are always sung as 1, 2, 3, 4, 5, 6 and 7. The trouble is that you may not be used to singing the rising and falling notes when you encounter a lot of rising and falling notes. The pitch is not easy to sing correctly. Personally, I suggest that the best way to learn classical guitar is to use the "fixed roll method". Because it is convenient to remember when singing and playing and reading music. When reading music, when there are ascending and descending signs, we should downplay the roll-call method and remember the interval relationship, scale relationship and harmony relationship more.
the first tune singing method, its roll name changes with the difference of "tune", and on which note the tonic of "tune" is, one (more) is sung with this tone. For example: 1 = c means singing the "c" sound by 1 (more); 1 = g is to sing the "g" sound by 1 (more).
The singing method of simple notation belongs to the first key singing method. No matter how the key changes, it always sings the tonic of the key as "Duo". When friends who are familiar with the notation learn the staff, it will be relatively easy to adopt the "first tune singing method". The trouble is that different tunes have to be memorized.