Why are vhs tapes sound more clear than dvds or bluray dvds sound?

Seriously! i jus got my old video player out now, and connected it to my HD tele. Usually on dvds or blu ray dvds when im watching them i need to keep putting the volume up and down. Sometimes the dialogue is not clear, especially when there`s alot of speacial effects like the movie Transformers etc..... Just testing Raiders Of The Lost Ark and i can hear every word spoken unlike dvds.