I am not that concerned at age 9 months if you are not hearing a lot of consonant-vowel combinations yet, although many babies do start to form single syllable consonant-vowels such as “ba”, “ma” or “na” in the 6-9 month period and by 10-14 months are actively babbling a variety of consonant-vowel combinations and/or saying first words. I am assuming you are hearing a lot of vocalizations of open vowels, “ooh, aahhh, uuuhhh”? You may sometimes also hear some gutteral sounds in the back of the throat like a “g” or “k” sound. You should hear variation in her voice even with the open vowel sounds, squealing, low pitches etc.
Is your daughter very mobile with crawling and learning to pull to stand at this time? Sometimes babies are quieter verbally when they are working on other motor skills such as crawling and learning to walk and all that motor energy is going into those skills and once they are mastered then the babbling begins in ernest. However, having said all that, in the next month if you are still not hearing any consonant sounds, you can call your local early intervention provider for a developmental evaluation just to rule out that she is showing any delays in her speech and language development. If your daughter has had frequent ear infections, this would also be another reason to seek an evaluation now, since fluid in the ears can greatly impact speech & language development. In the meantime, continue to talk to your baby constantly, sing songs with gestures such as Twinkle Twinkle Little Star or Row Your Boat, read books, always make sure she is looking at your face when you speak to her and play fun games with silly sounds-babble to her “bababa” and “mamama” even if she is not yet repeating it back to you. Even young babies have imitation skills and seeing your lips form the sounds is important. You can also build some simple baby signs into your daily routine such as the signs for “more”, “eat”, “drink” and “play”, you can find many websites online for baby signs and we as therapists often use this total communication approach to language with babies and toddlers (not just hearing impaired children).
This is a nice article related to how sound production is tied developmentally to feeding.