Hi,
I am a bit confused with the difference between the frequency (44kHz) and the bit rate (e.g. 320 kbps) in MP3 files. I have ripped most of my CDs at the 320 kbps bit rate but I am not sure if this is necessary (even when going through my reasonable HiFi). As I am streaming wirelessly to my raspberry pi from my desktop I am thinking that I am pushing the wifi dongle harder than necessary with the higher bit rate.
Any thoughts?
Ta,
Ian
My setup:
Raspberry Pi running Volumio
PCM2704 DAC connected to Mission Cyrus 2 amplifier
Edimax usb dongle streaming from Windows desktop
If you are satisfied with mp3 I suggest vbr.
But sample/bitrate >= 44/16 lossless is the better choice for good amps, speakers etc.
Audio quality is something subjective. CD quality audio is always sampled at 44.1 kHz. The mp3 (or AAC) compression works by reducing the accuracy of certain parts of sound that are considered to be beyond the hearing ability (of most people). It uses psychoacoustic models to discard or reduce sound components less audible to human hearing, and then encodes the remaining information in an efficient manner. So it’s still 44.1 kHz, but less sound information and thus requires less bandwith.
I have always noticed compression artifacts in 128 kbps mp3 and in some 160kbps MP3s. 192kbps is my choice for best quality/efficient bitrate (and small file size). I haven’t detected any noticeable difference between non compressed wav or flac, and mp3 with bit-rates higher than 192kbps. (You actually can, if you listen carefully with good quality earphones).
However, I found that the iTunes encoder produces cleaner, crisper MP3s at the same bit-rate, than Windows Media Player. The best choice is of course to use a ripper that has codec plug-ins. There is a lot of good freeware stuff out there.
Also, after some testing, I found that AAC+ is better with bit-rates under 160kbps. You don’t get the echo/ringing artifacts from high frequencies like you do with mp3.
I disagree, what you say is partially correct regarding rock-pop music if we use 320kb bit rate but expecially with classic and jazz, the quality gap is noticeable to my ears.
It is noticeable expecially with a good hifi set up.
Everyone has their own needs and tastes 
In my hard disk there aren’t mp3.
Yes, audio quality is something subjective.I agree.
Inviato dal mio SM-N9005 utilizzando Tapatalk
Point taken.
Then you have the issue with hardware. Most DACs and PC sound interfaces priced less than a couple of hundred Euros fail miserably to come close to the published specs for the chips they use. The board design matters much more than the chip. I’ve experimented with various DAC boards like the Behringer UCA202 USB and the Xmos2/DAC Sabre 9023 http://www.raspyfi.com/building-my-reference-dac/ , but for various reasons settled with the excellent O2 Objective and ODAC combo. http://nwavguy.blogspot.se/2012/04/odac-released.html
And then you have the speakers and the listening room. I use my Volumio gear in the kitchen while cooking and (usually) having a glass of wine or three. Sometimes it’s Vespro della Beata Vergine di Monteverdi on the sound system and sometimes it’s Metallica S/M, depending on the mood I’m in.
And finally the coolness. I chose vacuum tubes instead of solid state in my Volumio amp for four reasons:
They sound better (This might be slightly subjective. But it is still true.)
They glow.
They are just cooler.
They glow.
Listening experience is subjective. 
For MP3:
192 kbps VBR are for most people not recognizable from the source unless very silent rooms and very good equipment is used.
256 VBR require careful choice of listeners, equipment and music genre to be recognizable (and even in that case, the difference has to be sought in comparison to the original, you cannot tell it’s “a defect”)
320 VBR is basically the best MP3 can achieve.
Better encoders use the bits in a better way and iTunes is the best or among the bests. LAME comes second.
Other codecs are available, the only you may care about is MP4.
It is more efficient at lower bitrates (<160 kbps), from 192 kbps and up is basically equivalent to MP3 (but I would still use it).
Again, iTunes is the best or among the best encoders and I would use that every time.
If you want original quality in less space, use FLAC (but it doesn’t work on iTunes), or use Apple Lossless (it should work on Volumio but I haven’t tried).
I was a supporter of OGG and other codecs as MPC but just forget about them. Even if they are still better (not sure), they are not widely supported.