Josh Coalson;212533 Wrote: > the reference for FLAC replaygain is 89dB. recent encoders store > the reference level in a tag REPLAYGAIN_REFERENCE_LOUDNESS I've never been quite sure why the replaygain people chose to express their target gain as SPL, since they do not directly control the SPL of the replay, but only influence it by their adjaustment. Somewhere, buried in the spec. is the REAL target that replaygain is trying to hit, -20 dBFS (as I remember). As I understand it, a recording that the replaygain algorithm scores at an "average" level of -20 dBFS will have a replaygain of 0.0 dB. Whether the resultant playback actually corresponds to 89 dB "average" SPL depends on the amplifier gain, speaker sensitivity, distance to listener (at higher frequencies), volume of the room (at lower frequencies), frequency response of the reproducing system, etc.
Most often, replaygain computes a negative value. This is because -20 dBFS is a rather generous amount of headroom, and many popular recordings can be mastered at a somewhat higher level without clipping even a single peak. I do have a few popular/jazz CDs which generate positive replaygain values, but in general, at no point do their peaks approach 0 dBFS. On one CD, the highest peak is around -6 dBFS. Actually, hasn't the movie industry tied an 83 dB SPL monitor level (not 89 dB SPL) to -20 dBFS on the digital recording medium? The movie industry wants a little more headroom so their explosions can have more impact. I believe the suggested SPL for radio/popular music is 89 dB SPL tied to -14 dBFS, so they just raised everything 6 dB, apparently feeling that 14 dB of headroom was sufficient for peaks. While movie studios seem reasonably good about following the 83/-20 guideline, radio stations and recording companies for the most part ignore the 89/-14 guideline, hence the need for something like replaygain in the first place. dBFS = dB referenced to Full Scale, i.e. that largest value that can be expressed by digital audio. So, by definition, all dBFS values are 0 or negative. db SPL = dB Sound Pressure Level, IIRC is referenced to the average human threshold of hearing. So by definition, all sounds that an average human can hear will have positive SPL values. http://www.jimprice.com/prosound/db.htm This guy gets it mostly right, except that digital audio signals are almost always SIGNED, so the highest possible value is not 1111 1111 1111 1111 (the twos complement representation of -1), which is actually the LOWEST possible signal above 0, along with +1. The highest possible signals are 0111 1111 1111 1111 (+32767) and 1000 0000 0000 0000 (-32768). -- Timothy Stockman ------------------------------------------------------------------------ Timothy Stockman's Profile: http://forums.slimdevices.com/member.php?userid=8867 View this thread: http://forums.slimdevices.com/showthread.php?t=20576 _______________________________________________ ripping mailing list [email protected] http://lists.slimdevices.com/lists/listinfo/ripping
