Yoselle Rosenblatt: Melech Elyon

[dchevan <dchevan...>]

I need help with a Yoselle Rosenblatt recording from Sept. 6, 1927 of a Rosh 
Hashanah prayer: Melech Elyon.  On the recording a choir conducted by Meir 
Machtenberg sings this big Verdi-esque melody for most of the piece, but 
exactly at the 2:00 minute mark on my CD player the choir stops and a boy 
soprano (Herbert Zlotnick) and Rosenblatt sing a hauntingly beautiful duet.  
Here's the problem I'm trying to solve: they are singing the words "Medaber 
b'Tzedakah, Lovesh B'Tzedakah."  In my Mahzor those words don't appear anywhere 
in Melech Elyon.  So, my question is, where does this passage come from? Does 
anyone familiar with the Rosh HaShanah liturgy recognize this phrase ( a 
beautiful image, I might add)?  I'd like to know where I might locate it in a 
Mahzor and maybe even a bit more about this melody.

Thanks,

David