When choosing a bitrate for your stream, it is worth understanding how Mp3 bitrate's work so you can make an informed choice on which bitrate to use.
In short, MP3 compression removes parts of the sound in an audio file that are not usually heard by the human ear. By removing these sections of data the file size will become smaller. An MP3's bitrate determines the amount of data the file may use per second of audio. This basically means that when an MP3's uses a lower bitrate it has less data being transferred per second of audio. Therefore the file size will become smaller and the the subsequent quality of the audio will also be much lower.
MP3 (or MPEG-1 Audio Layer 3) is a digital audio encoding format that compresses data by basically removing parts of the file in order to make it a smaller size. This allows for the file to require less space for storage on a computers harddrive or personal MP3 players. It also allows for this kind of data to be transmitted across the internet with less bandwidth.
When music is encoded into MP3 (from an audio CD for example) you are given an option as to how many kilobits (kb) the file may use per second of audio and the sample rate. The most common sample rate used is 44.1khz as this is also used for audio CD's. The bitrate options that you are given can be user specified from anything as low as 32kb upto as high as 320kb. An Mp3 file encoded at 320kb is considered to be as close to the original recording from the CD as possible in this format.
This type of data compression is also applied in 'Internet Radio' streaming. When audio is compressed in such a way through a streams encoder (regardless of the format the audio's signal is coming from) the lower the stream bitrate used, the lower this will be in the occurring sound quality. The audio will begin to lose certain frequency’s through the compression. Any really low frequency’s such as a bassline in the music will begin to sound less defined and the high end frequency’s will begin to show the compression artifacts more evidently. Particularly with electronic music you will notice that the hi-hats and cymbals will begin to sound odd and kind of digitally distorted.
Having said this, the perceived quality can also dependant on the listeners own awareness of this data compression and also on the equipment that a stream is being played back on. For example the artifacts of a low bitrate Mp3 stream would be more noticeable on a good set of speakers more so than on some laptop speakers or a digital radio.
Below is a short piece of music that we have created with a wide range of frequency content for demonstrative purposes of varying bitrate quality’s. The music has been encoded into Mp3 from the original 16 bit .wav file with a sample rate of 44.1khz and at four different bitrate's ranging from 32kbps up to 256kbps. Have a listen to each and see if you can notice the difference.
The most commonly used bitrate is 128 kbps. Most people have difficulty telling the difference between 320 kbps and 128 kbps. Anything below 128 kbps becomes more noticable. We therefore recommend you use 128 kbps if you are unsure as this gives a happy medium of sound quality and good compression.