Rockbox mail archive
Subject: Re: Frequency as it relates to recording quality
From: ajf (ajf_at_midmaine.com)
The sampling frequency is the number of times per second an audio is
sampled. CD audio is sampled at 44.1 KHz, which means 44,100 samples per
second. CD audio uses 16 bit samples, so the size of an uncompressed CD
audio file is 44,100 x 16 bits per second x 2 (stereo) or about 10 MB per
According to Shannon's Law, we can hear sounds at a frequency up to 1/2 the
sampling rate, which makes 44.1 a good choice, because the range of human
hearing tops out under 20,000 Hz and declines as we get older. If you were
recording human speech, you might use 22.05 KHz sampling, because the
highest frequencies usually encountered are around 8 KHz. That would halve
the size of the file.
The "bitrate" refers to the degree that the file is compressed. The lower
the bitrate, the more the file has been compressed and sound quality is
lost, but the smaller the file. A 128 kbps mp3 will run about 1 MB per
minute (128 x1024 x60 / 8 bits/byte) , a 10-fold reduction, but the sound
difference from the original will be apparent.
Most experts agree that at bitrates above 192 kbps, any loss of quality is
hard to detect, but at that bitrate, the file will be 50% bigger.
It is a trade-off of size vs quality.
David Reis writes:
> Can anyone give me some quick details on how the frequency affects the
> recording quality.
Page was last modified "Jan 10 2012" The Rockbox Crew