It *is* a separate flavor from the salt (sodium chloride) that creates the umami flavor. It's monosodium glutamate (aka MSG or Accent).
I've had a recipe for Chinese brown sauce for stir-fry for at least 15 years. After years of using it, it seemed like it didn't have enough savory flavor (my cooking and taste buds were improving
), so I would add more soy sauce to the 6 tbsp already in the sauce. It just tasted saltier.
Then I started to make more Asian foods and bought some oyster sauce for another recipe. I decided to add some to the stir-fry sauce - only 1/2 tsp - and the difference was amazing! So much more flavor - deeper and more rounded.
There are actually two forms of glutamate and different umami-rich foods usually have one or the other. Combining the two boosts the flavors even more.
Thanks for the link, ppo!