I did not get many responses so will ask the question again in a different way.
I have noticed there are different ways to move your arm for a bass chord strum.
If you watch the Obla Di Obla da song lesson on the site for the G and D bass chord strum the bass strum is mostly wrist movement for both chords. Then watch Justin’s lesson on If It Makes You Happy by Sheryl Crow and for the bass G strum Justin uses full arm movement.
In my original post I asked when doing a bass chord strum with the open D chord should I use full arm movement or mostly wrist to pick the D string. It’s easy to do this with the open G chord because the bass is the top string. Not so much with the D chord.
This leads to the second question, why does Justin use full arm movement on the bass chord strum for If it Makes You Happy and mostly wrist for the bass strum in Obla Di? I think I might know the answer but will wait to hear what others might say.
In my opinion, strum however it’s most comfortable for you without sacrificing accuracy. Playing an open D chord probably requires a less wide movement since the thickest two strings are not played, whereas in the open G chord the root note is on the 6th string. Over time, you’ll find that you won’t make very wide arm movements even if you strum all 6 strings.
Obla-Di is faster and has the bass strums on every chord and requires more accuracy, hence the smaller motion. If it Makes You Happy only has the bass strum on the G chord and does not require a lot of accuracy. Also, the latter seems to have a “big strum” feel to it and Justin keeps that arm moving a lot throughout. Obla-Di seems to have a faster, lighter touch.
You should use whichever method feels most comfortable and most efficient to you, and generates the sound you want to hear. Justin uses the motions he uses for those reasons as well, I would assume.
Personally, I choose my picking arm, wrist, hand, finger, and pick motions based on what allows me to generate the sounds I want to produce with the least effort possible. As I analyze all of these things during focused practice, I may watch other players’ techniques for ideas, but in the end, I settle on a method that feels best to me, not because “so-and-so” did it that way.
Another thing that can affect how you answer this question for yourself is to consider the subtle difference in sound you get if you pick the string and stop the pick on the next string, pick the string and quickly move the pick away from the strings as your arm continues to move, pick the string and slightly graze the string just below, how many other strings you’re muting while you pick that string, etc. These subtle differences in technique can have a big effect on what sounds come out of your instrument, and you’ll have to decide which method provides the sound you want in every circumstance.
This is an interesting “down the rabbit hole” chat, but there is no RIGHT answer.
If it makes you happy has a very laid back groove(long strumming pattern) and Ob-la Di has more of an alternating bass. Quick short strums
Two different styles two different strumming techniques.