Talk:Bit rate: Difference between revisions

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could someone add bitrate info for MPEG? and explain that same bitrates dont have to mean same quality - cd has bitrate of 174kbytes/s, encoded to MusePack or OggVorbis could have almost the same quality in 1/10 size. Similar with mpeg vs divx.

could someone explain what bitrate means in terms of audio recordings? -- Tarquin 13:18, 12 Aug 2003 (UTC)

Could someone explain the meaning of the phrase "The bitrate shows how large the quantity of the stored bits per second of music is." Talk about obtuse phrasing! Dostal 21:11, 8 Jul 2004 (UTC)

Bitrates

This section could do with some work. Most, other than marketers, don't consider 128k to provide CD quality, irrespective of codec. Ok, there is the language 'minimum possible'; but then on the other hand, it gives 8Mbit/s as the 'minimum possible' for DVD quality, when this is more like the _maximum_ possible DVD bitrate (and 'DVD quality' can arguably be had for far less with a more efficient codec such as MPEG-4). Blorg 16:37, 16 Nov 2004 (UTC)

A lot of the figures, especially in the Video section, were intended to be ballpark values. If you know of more accurate lower bounds, feel free to change them. I really don't want this article get involved in silly "CD quality" flamewars, so how about specifying that "Foo quality" means "more than 50% of casual listeners do not consider the quality to be inferior to Foo". Obviously if you're an expert with brilliant equipment and you know precisely what to listen for, you will be able to tell a difference whatever the bitrate, but that's really not the point. [[User:Smyth|– Smyth]] 19:24, 16 Nov 2004 (UTC)

Why not simply change the CD quality to 320? Since that is the de facto quality of most CDs recorded nowadays (methinks...). (--HJV)

What do you base that number on? I think you're missing my point: the idea behind keeping it at 128 is that it is a number that most casual listeners would not notice to be inferior to the original, unless they were actively searching for differences. This page is supposed to be an indication of what's possible with the state of the art, which is no longer MP3. – Smyth\^talk 1 July 2005 08:38 (UTC)

Just to get this clear. Is the article trying to tell what the quality of the audio on the CD actually is? In that case it should be 320. If it's trying to say what the human ear distinguishes as "CD quality", then leave it 128... Just to give an example, you can't refer to a 262 144 colour screen as a 65 536 colour screen despite the fact that the human eye will most likely not see any difference between the two. :)--HJV 2 July 2005 01:42 (UTC)

"In that case it should be 320."

How do you figure? 44100 Hz * 16 bit * 2 channels = 1.4 Mbps

(But don't try that on google calculator!) - Omegatron July 2, 2005 04:05 (UTC)

It's what the human ear distinguishes. There are explanations in the article itself, in a comment in the article, and a few paragraphs up on this talk page; I think it should be pretty clear. – Smyth\^talk 2 July 2005 11:52 (UTC)

I don't see any of these explanations. Do you mean "that is the de facto quality of most CDs recorded nowadays (methinks...)"? That's hardly an explanation. - Omegatron July 2, 2005 14:13 (UTC)

Are you mistaking me for HJV? :) – Smyth\^talk 2 July 2005 17:04 (UTC)

No. I'm asking where the explanations are. - Omegatron July 2, 2005 19:34 (UTC)

Maybe I'm misunderstanding you. The explanations I was referring to are, on this page, 'how about specifying that "Foo quality" means "more than 50% of casual listeners do not consider the quality to be inferior to Foo"', and on the article page, 'The bit rates in this section are approximately the minimum that the average listener (when using state-of-the-art compression) would consider not significantly worse than the reference standard'. Both of those sentences were written by me, so whether they're a good idea or not is obviously up for debate, but I think HJV is missing the point. Or perhaps he's under the delusion that since 320kbps is the maximum bitrate of MP3, that it is in some way equivalent to a CD. – Smyth\^talk 2 July 2005 20:07 (UTC)

Ahhh... But that's pretty much opinion, no? That's not the actual bitrate at all. It's just the information degradation that an "average human" can't distinguish. Hmmm... - Omegatron July 2, 2005 20:56 (UTC)

Yes, of course it's subjective, but subjectivity is what lossy encoding is all about. Now technically this article doesn't have to mention lossy encoding at all, but audio and video bitrates, and their corresponding subjective qualities, are things that the average user will have a fair amount of experience with, so I think it's a good way of explaining what would otherwise be a fairly abstract concept. – Smyth\^talk 2 July 2005 21:35 (UTC)

bandwidth vs. datarate

I think there is a quite bad mixup here. These bandwidth conversion links only offer datarate conversions! the bandwith - datarate relationship depends on the modulation ... Unfortunately this inaccuracy of definitions is all over these articles here!

Mathematically, for a given bandwidth; sampling at 2-times that bandwidth is the maximum sample-rate needed, beyond that no extra information is being recorded. In order to understand why this is you have to understand the mathematics of working in the frequency domain(rather than time domain), but essentially, a 22khz bandwidth signal (such as a sound signal which is human-hearable, humans can only hear between about 20Hz and 22Khz, which is why CDs are sampled at 44.1Khz) sampling beyond 44Khz is useless. Of course, this is given that the sampling being done is 'ideal' mathematically.(In addition, any particular individual might be able to hear beyond 22Khz. However, this begs the question; what musician is intentionally producing sounds above 22Khz??) The extra .1Khz(100Hz) is more than enough to account for the non-idealities of current digital sampler technology.

sampling beyond 44Khz is useless
- Except for reducing quantization noise, phase distortion, and aliasing, providing a guard band...
what musician is intentionally producing sounds above 22Khz
- All of them. Harmonics extend to infinite frequency, though the amplitudes become negligible.
The extra .1Khz(100Hz) is more than enough to account for the non-idealities of current digital sampler technology.
- I'm not sure about that. — Omegatron 05:20, 13 March 2006 (UTC)[reply]

Merging the little bit rate articles?

Bit rates (data-rate units)
Name	Symbol	Multiple
bit per second	bit/s	1	1
Metric prefixes (SI)
kilobit per second	kbit/s	10³	1000¹
megabit per second	Mbit/s	10⁶	1000²
gigabit per second	Gbit/s	10⁹	1000³
terabit per second	Tbit/s	10¹²	1000⁴
Binary prefixes (IEC 80000-13)
kibibit per second	Kibit/s	2¹⁰	1024¹
mebibit per second	Mibit/s	2²⁰	1024²
gibibit per second	Gibit/s	2³⁰	1024³
tebibit per second	Tibit/s	2⁴⁰	1024⁴

The (currently six) bit rate articles need work. The bit and byte rates, for instance:

kbit/s (1000 bits)
kbyte/s (1000 bytes = 8000 bits)

are currently clumped into the same kilobit per second article, which is suboptimal (though they aren't really worthy splitting into two articles I don't think). Maybe rename to Kilo- bit rates or something? Nah. That sounds even worse...

Also, none of the articles are consistent in formatting or information presented anyway. Maybe these should all be merged into bit rate? It was already decided to keep kilobit, etc. separate, but maybe the rates will never be big enough for their own articles. — Omegatron 05:25, 13 March 2006 (UTC)[reply]

Transcoding questions

If one is playing music (or speech for that matter) at any given bitrate, is there any point in recording it at a higher rate? Also, if the playing bitrate varies, should one record using a constant bitrate setting or a variable one? 87.74.35.221 19:43, 19 November 2005 (UTC)Eileen Caister[reply]

If it's lossy audio that's being played back, any non-lossless recording will result in objectively worse quality. Whether this is noticable with your ears is another problem altogether. --KJ 18:10, 25 January 2006 (UTC)[reply]

No binary meaning for SI prefixes

The entry currently states:

however, most Internet Service Providers, and software companies,
such as Microsoft use base 2 ...

I don't believe this is true and request any references to support the claim. I did some research, appended below, and found that a preponderance of evidence is contrary to this assertion, So I am removing this section. I assert that binary prefixes—both the new forms and the misused SI forms—are not conventional units when discussing bit rates.

The references cited below are an ad-hoc sampling of Google results using terms like site:microsoft.com "ISP service" mbps mbit/s megabit.

References regarding Microsoft usage of decimal and binary meanings for SI prefixes kilo, mega, and giga in the context of bit rates

http://www.microsoft.com/windows/windowsmedia/howto/articles/intstreaming.aspx

320Kbps (320000 bps)
148Kbps (148000 bps)
66Kbps (66000 bps)

These obviously use the decimal meanings.

http://www.microsoft.com/technet/prodtechnol/Netshow/evaluate/features.mspx

Produces near FM-radio quality with 28.8 Kbps modems and near
CD-quality at 64 Kbps.

"28.8Kbps" is a decimal usage refering to the V.34 standard modem speed. The other uses in the document presumably use the same convention.

http://www.microsoft.com/mspress/books/sampchap/6280.asp

Connection	Bandwidth
Dial-up	28.8 to 56 Kbps
ISDN	64 to 128 Kbps
DSL or Cable 	128 to 768 Kbps
T-1	1.5 megabits per second (Mbps)
T-3	45 Mbps
DS-3	45 Mbps

These are all decimal usages refering to standard bit rates, and this usage is consistent throughout this document when refering to fixed bit rates, e.g. for standard link protocols. Yet, the document also includes clear instructions for epsressing the bit rate of streaming media as Kbps of 1024 bits and Mbps of 1024 Kbps:

Samples per second * bit depth per sample * number of channels = total bits per second (bps).
Total bits per second / 1024 bits per kilobit =
total Kbps

Maybe the distinction in the author's mind (if any) is that fixed link speeds use decimal prefixes while content encoding bit rates use binary prefixes?

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnwmt/html/introwmt7-2.asp

The bit rate of high-resolution, full-frame, broadcast video is
about 128  megabits per second (Mbps). To download one second of
broadcast video over a 28.8 kilobit per second (Kbps) connection
using a modem would take one hour and 14 minutes.

At least the 28.8 Kbps reference is decimal usage. Other uses in this document are ambiguous.

http://download.microsoft.com/download/7/4/f/74fe970d-4a7d-4034-9f5d-02572567e7f7/19_CHAPTER_6_Optimizing_IIS_6.0_Performance.doc

The server is connected to the Internet through a DS1/T1 line,
which can transmit data at 1.536 megabits per second.

Decimal usage.

Connection Type  	Connection Speed
Dedicated PPP/SLIP via modem 	28.8 kilobits per second (Kbps)
Frame Relay or fast modem 	56 Kbps
Integrated Services Digital Network (ISDN) 	128 Kbps
Typical DSL 	640 Kbps
DS1/T1 	1.536 megabits per second (Mbps)
10-megabit Ethernet 	8 Mbps (best case)
DS3/T3 	44.736 Mbps
OC1 	51.844 Mbps
100-megabit Ethernet 	80 Mbps (best case)
OC3 	155.532 Mbps
OC12 	622.128 Mbps
1-gigabit/sec Ethernet 	800 Mbps (best case)

These are all clear decimal uses except for the Ethernet ones which are ambiguous (we don't know what "best case" means).

http://www.microsoft.com/technet/prodtechnol/winxppro/maintain/wificomp.mspx

The maximum bit rate for IEEE 802.11b is 11 Mbps (using DSSS).
The maximum bit rate for IEEE 802.11a is 54 Mbps ...

Decimal usage.

http://www.microsoft.com/mspress/books/sampchap/5202.asp

A T1 circuit (also called a T1 line) is formed from a combination
of 24 DS-0 (Digital Signal Zero) channels, each having a bandwidth
of 64 kilobits per second (Kbps), for a total bandwidth of 1.544
megabits per second (Mbps).

T1 = 193 bits/frame x 8000 frames/sec
   = 1544000 bits/sec 
   = 1.544 Mbps

Decimal usage.

References for ISP usage of decimal and binary meanings for SI prefixes kilo, mega, and giga in the context of bit rates

Comcast (US Cable TV and ISP)

http://www.comcast.com/MediaLibrary/1/2/CM/VanityURL/documents/FCC_Entire_Tariff.pdf http://www.comcast.com/Benefits/CHSIDetails/Slot5PageOne.asp

CAP AND SWITCHED ACCESS SERVICES TARIFF
 Definitions:
 Mbps: Megabits, or millions of Bits, per second.

Decimal usage explicitly stated.

Speed comparisons are for downloads only and are compared to 768Kbps
DSL and 56Kbps dial-up.  Maximum download speed of 4Mbps (or 6 Mbps)
and upload speeds of 384Kbps (or 768Kbps) depending on the product
that is selected.

The DSL and dialup rates are obviously decimal usage. The other uses in the document presumably use the same convention.

Meer.net (US ISP)

http://w3.meer.net/pricing.html

T1 speeds up to 1.544Mb/sec

Decimal usage throughout the document.

Optic Fibre & Wireless (Australian ISP)

http://www.ofw.com.au/e1.html http://www.ofw.com.au/bandwidth.html

This company's usage is almost entirely based on decimal usage of SI prefixes for bit rates, even though they define the terms kilobit and megabit with the binary usage.

What is E1?
E1 is a European Telco Standard that carries data at 2.048
Mbps over copper wire.

Optic Fibre & Wireless (OFW) can connect your organisation
together at speeds up to 2 Gbps (2,000 Mbps) or 20 x faster
than your LAN!

1.5 Mbps (1,500 kbps) - the bandwidth of business ADSL

So far they are using standard decimal prefixes. But then they go and define kbps in a glossary of terms:

kbps
(kilobits per second) A measurement of the transmission speed
of data measured in 1,024 bits per second.

This is using the SI prefix with binary meaning. Presumably, though, this entry is an error (or an actual misunderstanding of the term by the person who wrote this entry) since all of the actual uses of kbps on this page and elsewhere on the company's site use the decimal meaning (e.g. "56 kbps - the bandwidth of your dial-up modem").

Later, in the same glossary:

Gbps
(gigabits per second) This is a measure of throughput in
gigabits per second — 1 billion bits per second. (1,000 Mbps)

Which asserts the decimal meanings at least for Mbps and Gbps.

Internode (Australian ISP)

http://www.internode.on.net/adsl/pricing/home.htm

Definitions:
  * MB is Megabyte
  * GB is Gigabyte, 1 Gigabyte is equal to 1,000 Megabytes

This is a bit ambiguous but hints at standard (decimal) usage.

Maximum Possible Modem Speeds:

    * ADSL2+ Modem - 24000k/1000k
    * ADSL2 Modem - 12000k/1000k

This is using the decimal meanings for these standard DSL speeds.

ISWest (US ISP)

http://www.iswest.com/DSL.html

Wide variety of DSL speeds; 144 - 768 kilobits per second

This is using the decimal meanings for these standard DSL speeds.

usage notes table

congratulations, that is a well-used and clean table.