Bitrate of an Audio CD: a Simple Calculation - Audio T-Board - Internet's Friendliest Board on Audio and Electronics

Déjà Vu · August 22nd, 2002, 03:48 PM

the same question has been asked many times before, so we decided to post it to the FAQ forum...

the bitrate of an Audio CD is calculated like this:

44,100 samples/channel/second x 16 bits/sample x 2 channels = 1411200 bits/second

as it's uncompressed audio...

1411200 bps equals to:

1411200/1024 = 1378.125 kbps (kilobits/second)

1411200/8 = 176400 Bps (bytes/second)

176400/1024 = 172.265625 kBps (kiloBytes/second)

regards,

P.S. you can find further information on HowStuffWorks' "How CDs Work" pages

Cygnus X1 · September 3rd, 2002, 05:33 PM

In simple terms, perceptual audio compressors like MPEG-1 Layer 3 (mp3) and ATRAC work on the principle that you cannot percieve sounds in close proximity, both in the frequency and time domains. Thus, much of the data in uncompressed linear PCM (like CD) can be removed with little or no perceivable effect on the sound. For instance, if a mouse farts in a room at the same time a stick of dynamite explodes, you will not hear the mouse fart. By removing this data, less bits are needed to get the same sound (i.e. the dynamite). An encoder is given a certain amount of bits to play with, known as bandwidth. Each encoder format (AAC, MP3, OGG, MPC, EPAC, etc) has its own strengths and weaknesses, so that 128kbps for one encoder is not the same as 128kbps for another. The encoder's responsbility is to allocate bits in the best way possible to ensure that what you hear is as close as possible to the original signal. This concept is known as transparency. Once an encoder begins to run out of bits for a particular sound, an artifact occurs, much like what happens with MPEG video (blocks) or JPEG photos, which are also compressed formats. So, the greater the bandwidth, the more likely the signal will sound close to the uncompressed source. The point at which encoders reach transparency varies by format and implementation. . . .for AAC it is around 128kbps (with PsyTEL), MP3 is around 180-200kbps (with LAME), while the older mp1 (PASC) is 384kbps.

JoseC. · September 4th, 2002, 04:27 AM

So, in a nutshell, bandwidth has nothing to do with audio quality. It only gives you an idea of how fast should be your system to stream a certain file in real time. That is only relevant when some kind of net streaming is involved. When data compression is used, the most important thing quality wise is how the encoder does its job, i.e., how it decides what information should be discarded.

The point I want to make is that bandwith figures, mostly related to the different flavours of MP3, have no real meaning outside the MP3 realm. Comparisons between formats based on those figures are misleading and should not be used.

We all should be aware by now that it´s not only size what matters, but also the way it is used

JoseC.

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August 22nd, 2002, 03:48 PM	#1
Déjà Vu Guru Join Date: Jun 2001 Location: Istanbul, Turkey Posts: 2,614	Bitrate of an Audio CD: a Simple Calculation the same question has been asked many times before, so we decided to post it to the FAQ forum... the bitrate of an Audio CD is calculated like this: 44,100 samples/channel/second x 16 bits/sample x 2 channels = 1411200 bits/second as it's uncompressed audio... 1411200 bps equals to: 1411200/1024 = 1378.125 kbps (kilobits/second) 1411200/8 = 176400 Bps (bytes/second) 176400/1024 = 172.265625 kBps (kiloBytes/second) regards, P.S. you can find further information on HowStuffWorks' "How CDs Work" pages __________________ [ Déjà Vu: The Past is a Mirror of the Future ] [ Sources: Apple iPod 4G (40 GB), Sony D-EJ955 (Black), Sony MZ-R91 (Blue) ] [ Ear: Sennheiser MX500, Sony MDR-E838 (Black), Sony MDR-EX70 (Black -- Tape Mod), Sony MDR-EX71 (White) ] [ Head: Audio-Technica ATH-A500, Sony MDR-D66 ] [ resident Metallica fan / Mac fanboy / Linux geek ] "In a world without fences and walls, who needs Gates and Windows?" Last edited by skamd; October 17th, 2002 at 10:01 PM.

September 3rd, 2002, 05:33 PM	#2
Cygnus X1 Veteran Join Date: Aug 2002 Posts: 118	In simple terms, perceptual audio compressors like MPEG-1 Layer 3 (mp3) and ATRAC work on the principle that you cannot percieve sounds in close proximity, both in the frequency and time domains. Thus, much of the data in uncompressed linear PCM (like CD) can be removed with little or no perceivable effect on the sound. For instance, if a mouse farts in a room at the same time a stick of dynamite explodes, you will not hear the mouse fart. By removing this data, less bits are needed to get the same sound (i.e. the dynamite). An encoder is given a certain amount of bits to play with, known as bandwidth. Each encoder format (AAC, MP3, OGG, MPC, EPAC, etc) has its own strengths and weaknesses, so that 128kbps for one encoder is not the same as 128kbps for another. The encoder's responsbility is to allocate bits in the best way possible to ensure that what you hear is as close as possible to the original signal. This concept is known as transparency. Once an encoder begins to run out of bits for a particular sound, an artifact occurs, much like what happens with MPEG video (blocks) or JPEG photos, which are also compressed formats. So, the greater the bandwidth, the more likely the signal will sound close to the uncompressed source. The point at which encoders reach transparency varies by format and implementation. . . .for AAC it is around 128kbps (with PsyTEL), MP3 is around 180-200kbps (with LAME), while the older mp1 (PASC) is 384kbps. Last edited by skamd; October 17th, 2002 at 06:24 PM.

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September 4th, 2002, 04:27 AM	#3
JoseC. Rookie Join Date: Sep 2002 Location: Madrid, Spain Posts: 11	So, in a nutshell, bandwidth has nothing to do with audio quality. It only gives you an idea of how fast should be your system to stream a certain file in real time. That is only relevant when some kind of net streaming is involved. When data compression is used, the most important thing quality wise is how the encoder does its job, i.e., how it decides what information should be discarded. The point I want to make is that bandwith figures, mostly related to the different flavours of MP3, have no real meaning outside the MP3 realm. Comparisons between formats based on those figures are misleading and should not be used. We all should be aware by now that it´s not only size what matters, but also the way it is used JoseC.