two questions, what is the significance of 0db on the volume of my receiver, and how many db range is there from source material such as Spotify, Netflix movies, cds?
0dB properly calibrated with each channel level matched to 75dB using - 30dBfs pink noise equates to a maximum level of 105dB per channel. This applies to everything.
Movies and TV are mixed differently from music. Lots of modern music is pushed up to the about - 9 to - 6dB rms and will comfortably sit at about 85dB at - 20dB on an avr. TV is generally mixed with the dialogue at - 23dBfs and movies are mixed around - 27 to - 31dBfs rms, giving them greater dynamic range.
Per my own measurements, nearly all properly mixed movies will have dialogue average 75-85dB with the volume set to 0dB. It's up to the mixer/director to decide how much dynamic range to utilize. I've had several Christopher Nolan films (all of the dark night and batman films, and things like interstellar) utilize the full range across all channels and the LFE, with total peak SPL measurements during intense scenes with lots of LFE reaching 115-120dB at 0dB. Some films have quiet scenes where the levels are 50-60dB and the loudest rumbling scenes 115dB or greater.
Another thing many who aren't in the film mixing industry don't realize, is that the same level of calibration (75dB @-30dBfs) doesn't sound the same as it does in a small room (like a living room) vs a huge theater. Very large rooms like a movie theater tend to flatten out and "compress" the dynamics due to psychoacoustics.
Back when DVDs came out and home theater became a big thing, many mixers and directors noticed that a film mixed for the big screen when played back in a living room sounded nothing like it did in the cinema. Many people used to complain in the early to mid 2000s about having to ride the volume level. Most studios nowadays will remix a movie for bluray in a large home theater sized room in what's referred to as a "near-field mix". Usually the original mix engineer will remix the film so that the same presentation heard in a huge theatrical dubstage translates to the smaller home theater.
Without a near field bluray remix, the theatrical track played back in a home theater would have unintelligible dialogue without the loudest parts being unbearable, while the quietest parts would be lost completely. Secondly, the LFE must be modified because the room gain of small rooms causes excessive build-up that sounds unnatural, and mixers must also ensure that the mix plays well with bass management, which is absent in commercial theaters.
Generally, one should adjust their calibration depending on room size, a very small room like a bedroom should be calibrated to 69dB, a medium to large room 73dB, and a very big room 75dB.
A majority of TV shows (particularly action and sci-fi series) are a bit more restricted in their usage of dynamic range, most tend to keep their range within a 20-30dB window, and I've never seen a shows heavy action scene with lots of lfe exceed about 95-100dB.
Music is all over the board. Classical pieces can have as much as 30-40dB of dynamic range, while modern pop and rock usually is restricted to 9-6dB. Most music is mixed with wildly varying levels.
Netflix itself does not modify the dynamic range of TV and movies. One difference though is unlike DTS HD MA mixes, DD+ contains dial norm Metadata, which levels the volume of the whole program to the dialogue at - 27dBfs. That means most shows or movies should have an equal loudness of dialogue at 0dB on the volume knob, even though tv shows are mixed louder. One thing I have noticed is Netflix and Amazon's original shows generally utilize a bit more dynamic range than standard TV shows mixed for broadcast. Obviously, this is a good thing.
There are no standard rules for dynamic range. The guy mixing the film simply calibrated his system to 85dB and then mixes by ear until it sounds good to him. Tv studios generally mix at 76dB, but dial norm take care of the level difference meaning it should still sound good at - 6 to 0dB. If you want to hear the movie the way the mixer heard it in the studio, set the volume between - 6dB (for a room less than 2000 cu ft) and 0dB (for a room 3000 cu ft or greater).
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