[Flac-dev] Synchronizing a streaming client to the server Was: Idea to possibly improve flac?

[Brian Willoughby]

The hearing tests which established the 20 kHz limit were based on  
sustained, pure tones.  The 20 kHz limit is the average - some have a  
lower limit, some have a higher limit.  But that value is basically  
right for sustained tones.

The key is that our perception of audio is not completely described  
by our response to sustained tones.  Our brain also analyzes  
transients, even in the first one quarter cycle of a waveform.  Test  
have been done using manipulated digital data to show that humans can  
hear a difference if the transients are changed.  In other words,  
different percussive sounds are perceived differently, even if the  
only thing changed about the waveform is the first fraction of a  
cycle.  This is almost completely unrelated to sustained waveforms  
where every cycle is identical.  There's even some research showing  
that the polarity of the initial half cycle is important to perception.

The bottom line is that you end up having to preserve high  
frequencies that you might not be able to hear when they are  
sustained, just so you can preserve the full attack of percussive  
sounds.  It might seem like a waste of bandwidth if you focus on the  
pure tones, since we can't really hear those, but the transient  
response is the real key to recording realistic sounds.  The impulse  
response of a system describes how clearly it reproduces original  
sounds from nature.

Sorry for my quick attempt to summarize this.  A more thorough  
investigation of the research into human hearing and perception can  
be found in http://www.earthworksaudio.com/wp-content/uploads/ 
th_world_beyond_20khz.pdf

Brian Willoughby
Sound Consulting


On Jan 7, 2011, at 19:33, David Richards wrote:
> Also BTW if anyone has a link on some information about why 96khz  
> is better than 48/44.1 id like to see it, because I don't  
> comprehend why it would be. 24bit is a clear win to my ears... (but  
> don't bring it up on this list because I'd rather not digress into  
> madness)