On 17 Dec 2016 at 17:13, paul dove via EV wrote: > Typically, the full range of hearing can be reproduced using the frequencies > from 20 Hz to 20 KHz. Sound must be sampled at least double the highest > frequency present that needs to be reproduced, 44.1k (twice 20 kHz plus a > little extra) samples/second for good music quality. > > The average human ear can differentiate approximately 90dB of range from the > softest sounds to the loudest. Eight bits gives 48dB of range while 16 bits > gives 96 dB of range and is often used for sampling digital audio.
The effective usable dynamic range in a car on the highway, even in an EV, is about 30-35dB. Below that the audio gets lost in the car's background noise. I'm confident that 8 bit quantization would be plenty in a car, though no one I know of uses it for auto music systems. Frequencies above around 10kHz will be masked by the background noise, too. A 32kHz sampling rate would be plenty for a car, though again, no one I know of uses it. In fact if you're over about 45 or 50 years old, chances are you can't hear anything over 15kHz anyway. (I could barely hear 18kHz when I was a teenager. Today my hearing falls off at around 15kHz, and I'm lucky it's that high.) And by the way, stereo FM radio's bandwidth is ... yep, 15kHz. What matters in a moving vehicle is not the sampling rate, or the bit depth (quantization). It's the encoding bit rate and algorithm. Nearly all digital audio sources, except for CDs, use some kind of data compression. (MP3 and AAC are common examples.) The higher the compression, the lower the bit rate, and the more you can store on a given medium, BUT the more audio information is lost. This loss of audio information causes audible compression "artifacts." Artifacts are kind of hard to describe. To my ears it's a watery or burbling effect, or a sort of grainy noise that seems to surround certain kinds of sound. For very high bit rates and sophisticated compression algorithms, this effect is slight. In a car, it might even be inaudible at those high bit rates. For low rates, it's much more apt to be audible, though I've found that some people notice it more than others. To make things worse, audio that's been digitally compressed, decompressed, and then compressed and decompressed a second time (or more) sounds a LOT worse. The loss of quality doesn't just add. Data compression algorithms interact with each other, and not in a good way. So if you're listening to mp3 files (which are compressed) through bluetooth (which is also compressed*), you lose more quality than the sum of the two would suggest. I'm probably not explaining this very well, but the upshot is that bluetooth really does make your music sound worse than a good, clean wired connection will. So what does all this have to do with EVs? EVs are quieter than ICEVs, and without engine noise and vibration, they have a different noise profile. Thus it's worth putting more effort into getting good sound in an EV than in an ICEV. For that reason I recommend that you avoid using bluetooth and its secondary digital audio data compression in your EV. *Recent versions of BT claim that their audio compression is "lossless" or "CD quality." This is demonstrably untrue. Yes, it's less "lossy" than earlier BT versions, but it's still not true CD quality (uncompressed PCM). David Roden - Akron, Ohio, USA EVDL Administrator = = = = = = = = = = = = = = = = = = = = = = = = = = = = = EVDL Information: http://www.evdl.org/help/ = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Note: mail sent to "evpost" and "etpost" addresses will not reach me. To send a private message, please obtain my email address from the webpage http://www.evdl.org/help/ . = = = = = = = = = = = = = = = = = = = = = = = = = = = = = _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org Read EVAngel's EV News at http://evdl.org/evln/ Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA)
