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Audio Bit Rates

AudioStudies

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Audio Bit Rates

Audio Bit Rates and Uncompressed Files

Every second in an audio recording has a specific quantity of bits. When considering various types of sound files this is expressed as the number of kilobits of data per second (kbps). For example, a 128 kbps file has 128 kilobits stored for every second of audio. This is an example of an audio bitrate that defines the amount of data that is stored in the sound file.

Every audio file has an associated bitrate. Faster bitrates correspond to more data stored across the full frequency range. The more kilobytes that are stored per second the greater the potential for better sound quality of the file, within the limits of human hearing, for similar types of files. Uncompressed audio files include the following types:
  • Compact discs (CDs) have a bitrate of 1,411 kbps at a 16-bit bit depth. This was first established by Philips and Sony in 1980; and adopted as a standard in 1987.
  • WAV files were developed by Microsoft and IBM to enable computers to read pulse code modulation (PCM) data. High-quality WAV files have a bitrate exactly the same as CDs at 1,411 kbps at 16 bit. However there are variations of WAV files. The actual bitrate is determined by a specific formula which multiplies the sampling rate with the bit depth and the number of channels.
  • AIFF files, were developed by Apple, using the same uncompressed technology as WAV files. Much like WAV files AIFF files are another way for electronic devices to read PCM data.
Bitrate is determined by the sampling rate and the bit depth. The sampling rate is the number of samples taken in a second. For example, CDs have a sampling rate of 44.1kHz.

When it comes to audio and bitrates, size does matter. The more kilobits per second the greater the quality of the sound. For many casual listeners, a bitrate of 320 kbps is acceptable. Clearly, CD-quality audio with 1,411kbps will sound better, particularly to discerning listeners.

PCM (pulse code modulation) is the hierarchical format for uncompressed audio. All recordings initiate as soundwaves in an analog setting. PCM converts this information into digital format by sampling recordings.

Compressed Audio Files

MP3s
are a very common form of a compressed audio file, with a maximum bitrate of 320 kbps at 16 bits, substantially lower than that of the uncompressed formats. MP3s use a compression codec that removes frequencies while trying to preserve as much of the original recording as possible. This allows for reduced file sizes but sacrifices sound quality. MP3s are an example of lossy compression, because the compression scheme does not include all of the original information in the recording.

MP3s were very popular in the early days of the internet due to the small file size; enabling easier sharing across a then slower internet. MP3s are still used heavily by streaming services and digital music platforms making them one of the largest formats for DJ music.

Free Lossless Audio Codec (FLAC) is an open source compression method for audio files; with significant advantages over MP3 because original recording is unaffected by the compression (no information is subtracted). With FLAC the file size can be reduced up to 60% compared to the original uncompressed file (such as WAV).

FLAC has grown in popularity, in large part to the lack of licensing restrictions, and has become the primary way to offer compressed lossless audio. FLAC also offers extra metadata to be stored like album art which WAV files do not support.

Lossless Audio Formats

The following table depicts the more common lossless audio formats with the most relevant information:

Format Sample Rate Bitrate Type Open Source? Metadata?

WAV​
44.1 kHz (usually)​
1,411 kbps (usually)​
Lossless​
No​
No​
AIFF​
44.1 kHz (usually)​
1,411 kbps (usually)​
Lossless​
No​
Yes​
FLAC​
Up to 655,350 Hz​
1,411 kbps (usually)​
Lossless​
Yes​
Yes​
ALAC​
Up to 384,000 Hz​
1,411 kbps (usually)​
Lossless​
Yes​
Limited to ITunes​
WMA​
Up tp 96 kHz​
Up to 768 kbps​
Lossless​
No​
Yes​


Although FLAC has some advantages over WAV, WAV is found in many pro audio devices that are not capable of FLAC. Clearly, lossless is preferable unless file storage capacity is of concern, or lossless isn’t available for some venue. For example, most of the internet radio stations broadcast in a lossy format.

Lossy Audio Formats

The following table depicts the more common lossy audio formats with the most relevant information:

Format Sample Rate Bitrate Type Open Source? Metadata?

AACUp to 96 kHzUp to 529 kbpsLossyNoYes
OGGUp to 192 kHzUp to 500 kbpsLossyYesYes
MP3Up to 48 kHzUp to 320 kbpsLossyYesYes


AAC is capable of the highest bitrate of the lossy formats but is not open source.
 
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Jimbob54

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AAC
 

Killingbeans

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The more kilobytes that are stored per second the higher the sound quality of the file, for similar types of files.

I'd rather say the higher potential for sound quality as long as you operate below( ...above?) the thresholds of human hearing.

Direct correlation between bitrate and sound quality would assume source material with infinite bandwidth and infinite dynamic range + hearing of listener, playback gear and listening space also having infinite bandwidth and infinite dynamic range. Reality doesn't come even remotely close to that.

Semantics... I know.
 

voodooless

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It would be useful to actually explain where the bitrates of these uncompressed format come from. How are they comprised. For instance, Redbook:
2 channels x 16 bits per sample x 44100 samples per second = 1.411.200 bits per second or about 172 KBps
 

threni

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I'd rather say the higher potential for sound quality as long as you operate below( ...above?) the thresholds of human hearing.

Direct correlation between bitrate and sound quality would assume source material with infinite bandwidth and infinite dynamic range + hearing of listener, playback gear and listening space also having infinite bandwidth and infinite dynamic range. Reality doesn't come even remotely close to that.

Semantics... I know.
Not just semantics - I could transcode a 128kbps mp3 as a "hires" flac and it would have a lower sound quality than a regular (16/44 cd rip) flac despite having a higher bitrate.

re: "All recordings initiate as soundwaves in an analog setting."
Depends on what you mean by a "recording" but some music is created digitally and only lives in the analogue domain during playback.
 

Killingbeans

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Also, I'm not too fond of this part:
For many casual listeners, a bitrate of 320 kbps is acceptable. Clearly, CD-quality audio with 1,411kbps will sound better, particularly to discerning listeners.

Most people will struggle immensely with hearing a difference. It doesn't have anything to do with "casual" vs. "discerning". Instead it requires specific training in order to identify minute artifacts that even the most "discerning" listener wouldn't dream of focusing on unless they were told to do so specifically. When a difference is detected under normal listening conditions, chances are that it's the result of specific source material making the compression algorithm slip up causing "tells". It has nothing to do with the bitrate.

EDIT: Didn't notice you were talking about uncompressed 320 kbps? If so, disregard this post.
 
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voodooless

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EDIT: Didn't notice you were talking about uncompressed 320 kbps? If so, disregard this post.
Even so, the bitrate itself doesn’t tell you a lot. 320 kbps can have many configurations of channels, bit depth and sample rate. It can be used for 8 bit mono at 44.1 kHz. With noise shaped dither this should still sound very good. Much better than 16 bit 22.05 kHz probably.
 
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Blumlein 88

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Then you have something like Dolby Digital +. Supports 5.1 or 7.1 channels. Up to 1 mbps for 7.1 and I think 655 kbps for 5.1 channels. The bits are allocated somewhat on the fly to various channels as needed. While the bit rate if simply split between channels is not very high at something like 140 kbps per channel that is not how it works and it seems more effective than you might expect.
 
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AudioStudies

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At this juncture in time, my primary interest in knowing more about this topic is to help sort out which internet radio stations are best. I suspect bitrate is the most important of the criteria, but not necessarily the only thing to look for when evaluating an internet radio station.
 

voodooless

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Let's also not forget variable bitrate lossy compression, some of which @Blumlein 88 already mentioned, but there are plenty more :)
 

Jimbob54

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At this juncture in time, my primary interest in knowing more about this topic is to help sort out which internet radio stations are best. I suspect bitrate is the most important of the criteria, but not necessarily the only thing to look for when evaluating an internet radio station.
That would be the ones that play the music you like the most? Do you really care about the bit rate?
 

Jimbob54

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I do when some are going with 64 kbps. 128 kbps seems okay if I like the music.
Well yes, all other things being equal. But for music exploration give me content over quality. I remember some of the early music podcasts, way worse than medium wave radio but music beamed from another planet.
 

voodooless

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I do when some are going with 64 kbps. 128 kbps seems okay if I like the music.
Then again, 96 kbps AAC vs 128 kbps MP3… tough one.

Besides, many internet radio stations still pretend to air via FM and dynamic compres everything to hell for no reason whatsoever :facepalm:
 

fieldcar

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Lossy Audio Formats
No love for OPUS?

iu




AAC is capable of the highest bitrate of the lossy formats but is not open source.
OPUS goes up to 512Kbps, though, it really doesn't matter. Above 192Kbps, OPUS and AAC sound identical to me. (marginally better than MP3 @ 320Kbps IMO)
 
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AudioStudies

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hen again, 96 kbps AAC vs 128 kbps MP3… tough one.
And this is where I am kind of stuck, as you just can't go by bitrate alone. I have heard that AAC does better with lower bitrates than MP3. I wish there was an easy way to rank all this. I guess I do care about bitrate to a degree but fully realize that if the best bitrate is all I was after --- I wouldn't be doing Internet Radio. Nevertheless with the tens of thousands of stations available, it probably wouldn't hurt to choose some in the genres I like with the better bitrates, or better methodologies with lower bitrates.
 
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