Diane B asks ...
How is 'tha' pronounced?
This is talking about Josiah Whitby's voice.
Now Josiah is from Yorkshire. What we have here is second person familiar, (thee or thou,) of course. This is conventionally represented 'tha' in writing Yorkshire dialect.
I'm leaning on that old convention.
I want to suggest the dialect. Folks familiar with Yorkshire speech will fill in the blanks. Folks who don't know it will not be annoyed.
I'm not making any attempt to be phonetic. That is an ocean without any bottom and I don't intend to fall in.
If you wanted to hear it ... the word I've represented as 'tha' appears in this recording.
It's near the beginning. Listen to the bit that goes ...
"Well, me lad, I said ... it'll be a bit before tha' does that again, maybe."
Though the speaker uses the familiar 'tha' in that spot, he uses 'ye' or "you' elsewhere. '
Tha' was only for intimates.
You can also hear the familiar usage in this long and completely incomprehensible joke. It seems to occur in a couple places. One is about three-quarters of the way though. There, it's pronounced, rather clearly, 'thou'.