Thank you for your reply Bwells. Yes, it's an HO scale 4-8-4 Northern. I have captured pictures of the decoder in this forum from the stages of me applying details and new paint. https://www.modeltrainforum.com/showthread.php?t=24329
It's the manufacturer DCC decoder (most likely SoundTraxx) that came with the new drive train I purchased from Bachmann to replace from the original 3-pole motor and chassis back in the early 90's for my 4-8-4. However, the decoder was not equipped with sound. After years I have accepted for what it is and, now I want to upgrade it to a better decoder + sound.
I visited SoundTraxx's site. Looks like I'm geared towards to either the TSU-750 Micro-Tsunami (because of the oil tender's awkward cylindrical size, this may work) or the TSU-1000.
Curious to know if you know if ESU Loki decoder are good?