Consider a WAV file obtained from a standard redbook CD with 16 bit samples and 44.1 kHz sampling rate. How do you compute the bitrate of the uncompressed stream?
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I don't think there's such a thing as standard redbook FLAC file, as redbook is a standard for pcm audio cds. If the size of a given flac file is X MBytes and it's audio duration S seconds, it's average bitrate in Mbits/s will be (8 * X) / s– audionumaOct 27, 2015 at 17:23
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@audionuma I now clarified the reference to redbook CDs in the question. Given the info in the question, is there a way to compute the bitrate without knowing the actual size of the FLAC file?– landroniOct 27, 2015 at 19:55
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3 Answers
Here is how you calculate the constant bitrate (CBR) of uncompressed audio:
Bits Per Second (bps) = Sample Rate (Hz) * Word Length (bits) * Channel Count
Which for 44.1 KHz, 16 bit, 2 Ch. (stereo) audio gives you:
44100 * 16 * 2 = 1411200 bps or 1411.2 kbps (kilobits per second, i.e. bps / 1000)
To express that in bytes, kilobytes or megabytes use the following conversions:
Bits to bytes: bits / 8 or bits * 0.125
Bits to kilobytes: (bits / 8) / 1000 or bits * 0.000125
Bits to megabytes: (bits / 8) / 1000000 or bits * 0.000000125
Which for 44.1 KHz, 16 bit, 2 Ch. (stereo) audio gives you:
1411200 * 0.125 = 1764000 Bps (bytes per second)
1411200 * 0.000125 = 176.4 KBps (kilobytes per second)
1411200 * 0.000000125 = 0.1764 MBps (megabytes per second)
The following tools may be to assistance calculating these numbers:
answered Oct 28, 2015 at 8:20
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Why does the number of channels enter in the equation? Is it that on recording (i.e. on ADC) the microphone registers two separate streams of audio?– landroniOct 28, 2015 at 9:17
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Sort of - you have a stream for each side (left and right) in the stereo image. A true mono audio file would only contain one stream. Surround sound comes in several formats with more than two channels, but these are rarely used for music alone. Oct 28, 2015 at 9:21
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1I thought a kilobyte was 1024 bytes and a megabyte was 1024 kB except in hard drive marketing and packaging. Oct 28, 2015 at 11:55
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@ToddWilcox - Yeah, there is a lot of confusion around that. Take a look at this article for some explanations: blogs.gnome.org/cneumair/2008/09/30/… Oct 28, 2015 at 12:11
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1@MichaelHansenBuur, that first
441000should be44100. (I'd correct it myself, but SE doesn't allow an edit that short.) Apr 4, 2019 at 12:34
Unless I'm getting my math terribly wrong, since standard CDs are stereo these days and there are 44100 samples in a second, each worth 16 bits, then:
2 * 16 * 44100 = 1411200 bps
Which in turn represents 1411.2 kbps (which is in kbit/s). In bytes, it would be 176.4 kBps.
The bitrate of a FLAC encoded file versus the bitrate of the source PCM file depends on the audio content.
In average, depending on the FLAC encoder settings, the ratio FLAC / PCM is around 65 %. See https://xiph.org/flac/comparison.html and http://www.synthetic-soul.co.uk/
So a 1411 kbps audio cd should on average produce an approximately 920 kbps FLAC file.
edit :please notice that this answer was produced before the original post was heavily edited and has in the process removed any reference to flac.
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What I'm interested really in the bitrate of the decoded FLAC file, the uncompressed stream. How is that computed? (I realize that my question may be slightly confusing. I tried to make the question clearer still and switched to WAV as example file.)– landroniOct 27, 2015 at 22:31
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It's a nice answer and provides some good references, but why don't you edit the answer then to match the question?– ZaellixAMar 29, 2021 at 22:23