Digital Recording Basics
Audio CDs -
Audio CDs are saved as a 16-bit, stereo WAV file sampled at 44,100 Hz,
for a sampling bit rate of 1.411Mbs (44.1 K/sec x 16 bits x 2 channels).
CDs are 650 MBytes and hold 74 min. of music plus a CDDB (CD Database) file containing the song titles.
See Compression algorithms below reduce size to
Compressed Audio -
MP3 (MPEG-1 audio Layer-3),
WMA (Windows Media Audio) and AAC (Advanced Audio Coding)
are three popular ways of compressing audio files. There are many more (see below).
They both can compress files by a factor of 5 to 20 depending on the quality desired.
MP3 is normally recorded at 128 Kbs for near CD quality and 64 Kbs for FM quality.
Higher quality MP3 can be recorded at 192 - 320 Kbs.
Although this is much lower than the 1.4 Mbs for CDs, it sound good because
it compresses by discarding signals
that are barely noticeable to the human ear.
The MPEG-4 (.m4b) format is recommended for iPod and iTunes users who want bookmarking, which is the ability to keep track of where you last left off listening to audio books or podcasts.
WMA is a lossless format
better for low bit rate encoding (16 - 64 Kbs), while MP3 is better for high bit rate
(128 - 320 Kbs) encoding.
Variable Bit Rate (VBR) encoding encures consisteltly high audio quality by making
intelligent bit-allocation decisions during encoding. VBR quality can be set from 1-100.
VBR files may be larger than
Constant Bit Rate (CBR) files at comparable encoding speed. e.g. at 128kbps a
CBR file will usually be smaller than a VBR file at 50.
The way the audio is compressed and stored is call the codec which determines how small the file size is. Some file types always use a particular codec. For example, ".mp3" files always use the "MPEG Layer-3" codec. Other files like ".wav" and ".dct" files support selectable codecs. For example, a ".wav" file can be encoded with the "PCM", "GSM6.10", "MPEG3" and many other codecs. Be careful not to confuse the file type with the codec - it often surprises people to know you can have a "MPEG Layer-3" encoded ".wav" file.
iTunes - .m4a (ACC) music files:
- M4A is generally regarded as the successor to MP3 but compared with MP3, M4A can compress audio with the same bit rate in smaller file size.
- M4A format files typically have stereo bit rate of 128kbps, 192 kbps or 256kbps. By the way, Bit rate is the amount of data that is conveyed per unit of time.
To put it another way, if you try to get the same sound quality, you need 256kbps bit rate when encoding with MP3 while only need 192kbps with M4A
iTunes uses a 256 kbps bit rate. This is an average bit rate encoding scheme, not a fixed bit rate encoding scheme. The actual sample rate is varied dynamically based on the content and time.
- M4A is typically encoded with Advanced Audio Compression (AAC) lossy compression, though lossless
- ALAC may M4A audio can be set as iPhone Ringtone directly just by renaming the file extension from M4A to M4R.
- The iTunes catalog was initially offered in 2003 as 128 kbps AAC files, many of which
were encoded from the original CD masters.
As of 2012 the audio files sold in the iTunes store have been encoded using the AAC codec with a 256 kbps Variable bit rate (VBR) and distributed with .m4a extensions from the iTunes store.
- Programs that open M4A files include iTunes, Quicktime, Windows Media Player, and Roxio Popcorn, Toast and Creator.
To play audio on Android Samsung, HTC, etc. you may want to convert video to more friendly audio formats like MP3
- Most people with average audio systems can't tell the difference from a CD and 256kbps ACC file.
People with high end systems ($ thousands) say the difference is noticeable.
Apples's Mastered for iTunes 5.0
- If you want to convert old files to 256 kbps, can't you just buy a year of iTunes Match and let it upgrade EVERYTHING to 256 kbps? There shouldn't be any cost at all beyond to $25 for Match.
M4A was generally intended as the successor to MP3, which had not been originally designed for audio only but was layer III in an MPEG 1 or 2 video files. M4A stands for MPEG 4 Audio.
Both M4A and MP3 file extensions are used for audio-only files. Audio-only MPEG 4 container files usually have an M4A file extension. M4A files are unprotected. Protected files usually have an M4P file extension.
AAC or M4A file quality is better and file sizes smaller compared to MP3 files. M4A files sound better than MP3 files when encoded at the same bit rate due to some of the enhancements made to the format.
See: What is M4A? What Opens a M4A? File Format List from WhatIs.com
What Is M4A? M4A vs MP3, Is M4A Better than MP3 or Not?
An Overview of Audio File Formats Supported By iTunes | Kirkville
Audio Sample Rates: Digital Audio | Apple
Source: File Formats at NCH Swift Sound
CD Qual (44.1 kHz 16-bit stereo WAV).:
AAC (m4a) 128 kbs
MP3 160 kbps 9:1 coompression 1.5 MB/min
AAC 96 kbps
MP3 128 kbps 11:1 compression 1MB/min.
WMA 128 kbsp 750K/min
WAV 1:1 compression 10MB/min.
(AAC compressed audio at 96 kbps generally exceeded the quality of
MP3 compressed audio at 128 kbps. )
MP3 96 kbps 700k/min.
WMA 96 kbps 700K/min
AIFF @44.1 KHz using μLaw 2:1 16-bit 300M/hr.
AIIF @44.1 kHz using IMA 4:116-bit 180M/hr.
AIIF @24 kHz using IMA 4:116-bit 88M/hr.
AIIF @24 kHz using IMA 4:116-bit mono 44M/hr.
AIIF @11 kHz using IMA 4:116-bit mono 20M/hr.
AIFF @44.1 KHz using MACE 6:1 8-bit 57M/hr.
toll quality telephone (8 kHz 4-bit u-law) 64 kbs
cell phone quality (8 kHz GSM6.10) 13 kbs
See Song Capacity Calculator
Other Formats and Terms
- Dolby Digital sound with five primary speakers (front and rear/left and right plus center) and an LFE (suboofer) channel.
- AA - Audible Audio
- Audible file format (audio books) (Audible.com)
- AAC - Advanced Audio Coding
- An audio compression technology that is part of the MPEG-2 and MPEG-4 standards. AAC, especially MPEG-4 AAC, provides greater compression and superior sound quality than MP3.
ACC is at the core of the MPEG-4, 3GPP, and 3GPP2 specifications and is the new audio codec of choice for Internet, wireless, and digital broadcast arenas.
- Adaptive Transform Coder 3 (relates to the bitstream format of Dolby Digital)
- ADPCM - Adaptive Differential Pulse Code Modulation
- takes up less storage space than the regular PCM format used by WAV and AIFF files.
Many MP3 players use ADPCM for their voice-recording feature.
- AIFF/AIFC - Audio Interchange File
- An old uncompressed digital audio file format from Apple. Similar to Microsofts WAV. AIFC is a compressed version.
- ASF (Advanced Streaming Format)
- ATRAC3 (Adaptive TRansform Acoustic Coding)
- 20:1 compression
- AU Basic Audio
- 8-bit u-law. Old format from Sun.
- Audible Audio Books
- The format of audio on a standard commercial Music CD (RedBook CD).
- FLAC (Free Lossless Audio Codec)
- An Lossless audio compression technology from the Xiph.Org Foundation (www.xiph.org). Files are much larger than MP3.
- Low Frequency Effects. Frequencies from 10Hz to 120Hz, normally sent to a subwoofer. The 1 in 5.1
- A method of file compression in which audio data is not permanently discarded. While keeping all of a song's information results in a much bigger sound file, if preserving full audio fidelity is of highest importance, this is the way to go.
- Apple iTunes AAC and Lossless format
- Monkey's Audio
- (.ape) - Lossless Compression format
- MP3 MPEG-3
- MPEG Audio Stream, Layer III
- MP4 - MPEG-4
- MPEG-4 is a Video format but has an audiio component
- MPA - MPEG Audio Stream, Layer I, II or III
- Ogg Vorbis (OGG)
- open-source audio format created in response to the 1998 announcement by Fraunhofer to begin charging licensing fees for the use of its MP3 format.
- Recording Industry Association of America, an organization representing many music labels, from small indies to the majors. Find out more on its Web site.
- An audio file, a MP3, most likely, in talk show format, along with a way to subscribe to the show and have it automatically delivered to your computerplayer. It uses RSS (see below). See PodcastingNews.com for software to let you subscribe to and manage podcasts on your PC.
- RealAudio 10. RealMedia Streaming file.
- RSS - "Really Simple Syndication" or "Rich Site Summary"
- A lightweight XML format designed for sharing headlines and other Web content. Used by Netscape to fill channels for Netcenter,
- SD2 - Sound Designer II File
- Can be played in QuickTime
- SHN - Shorten files
- It is a lossless compression algorithm for digital music developed by SoftSound.
- VQF- Vector Quantization File
- Transform-domain Weighted Interleave Vector Quantization (TwinVQF) Music File
- WAV - Waveform Audio
- PCM Wave audio. This is a raw audio file often used as the source for encoding other formats or burning CDs. There are several types of wav formats. The most common is PCM (44.1kHz,16 bit, stereo) at 600 MB per hour of audio.
Others include low quality MP3 at 11.5kHz, 16kBit/s mono.
- WMA - Windows Media Audio - lossless
|Format ||Compression factor ||CD quality Rate
Digital Music: Can You Hear Above 16-bit/44.1kHz? - The Mac Observer
Creating the right file (audio)
and Audio File Types
PC Audio Primer
File Formats at NCH Swift Sound
Audio Video over the Web under networks/internet
Digital Audio (MP3) Players:
Bill Machrone's SpA: Serious Personal Audio
MP3 Audio Page
Making WAV files from CDs
Understanding Digital Audio Formats
Audio Formats and at wisc.edu
Audio Input/Output Level Table
Connecting your PC to a receiver
NTSC Video (6 MHz)
Aspect Ratio: (3V x 4H)
A standard NTSC TV has 525 Horizontal Scan Lines (483 visable others contain sync signal)
(PAL has 625 lines)
Effective resolution is 483 x .7 (Kell factor) = 338 lines of resolution.
(Kell Factor says that only 70% of detail is perceived
because of information lost between scan lines.)
30 frames/second (2:1 interlaced - 1/2 of frames every 1/60 sec.)
Horizontal Resolution (vertical lines) varies:
Older TV's are capable of 300 vertical lines
Newer TV's have 400 lines and 27" and above "Hi Res." Std. TV's
have 600-750 lines.
Cable TV: 250 (330)
S-VHS: 320 (400)
Hi8: 350 (380-440)
Digital 8: (400-500)
DVD: 480 (250-400)
(most disks are recorded at 480 lines.
DVD players may be capable of 540 lines resolution)
(Horizontal resolution is measured based on a square screen, but actual
resolution is 1.3 x because of the aspect ratio of 3:4)
400 lines of resolution requires 400/.75 (aspec ratio)/ .7 (Kell factor) = 760 pixels)
DVD can use MPEG-1 or MPEG-2 compression, but most use MPEG-2.
Resolutions can be:
NTSC - 720x480, 704x480, 352x480 or 352x240
PAL - 720x576, 704x576, 352x576 or 352x288
See: Video Resolution at hometheater.about.com and here.
Composite - Color and syncronization signals mixed (RCA phono connector)
S-Video: luminance (Y) and color information (C) transmitted on separate
channels (4 pin Hosiden Connector )
Component YUV - 3 channels Y is the luminosity of the black and white signal.
U and V are color difference signals (RCA plugs)
Resolution: 480i, 480p, 576i, 576p, 720p, 1080i and 1080p depending on input.
RGB - 3 channels Red/Green/Blue
HDMI&tm; - High-Definition Multimedia Interface.
HDMI is backward-compatible with most current DVI connections.
DVI - Digital Visual Interface
A conventional NTSC image has 525 lines scanned at 29.97 Hz
with a horizontal resolution of 427 pixels.
This gives 3.35 MHz (assuming 2 pixels per video cycle) as a minimum
bandwidth to carry the video information without compression.
HDTV (US Version) (6MHz / 19.4Mbs)
(HTDV signals are compressed to fit in the same 6MHz channel as std. TV)
Broadcasters must convert to HDTV by 2006
Aspect Ratio: (9V x 16H)
HDTV is broadcast in two flavors: 1080i (interlaced) and 720p (progressive).
1080i has vertical resolution of 1125 (1080 active) lines, so can show more detail.
But 720p has a faster frame rate (6o frames per sec0 vs 30 frames per sec),
so it is better for fast-moving action, and is free of field artifacts.
Newer HDTVs are 1080p with 60 fps, so can display both formats.
480 progressive (480p) (SDTV) Standard digital TV signal
Max. - 1080 interlaced (1080i) signal
Horizontal Resolution: Max. 1920
Current HDTVs - 1200 - 1600 Lines
Uses MPEG-2 to compress signal to 19.4 Mbs
Transmitted over a 6 MHz UHF channel using a 8-VSB signal.
A standard (NTSC analog) signal is sent over the old VHF/UHF channel
while the HDTV (digital) signal is simulcast over a UHF channel (14-70)
In New York channels are allocated as follows:
Station Analog Digital
WCBS 2 56
WNYW 5 44
WNBC 4 28
WABC 7 45
WPIX 11 33
WNYE 27 24
By FCC mandate, TV manufacturers are forced to include ATSC tuners to pull in over-the-air signals into all 25 to 35-inch TV's by July 1, 2006, in addition to the standard definition NTSC tuners.
ATSC uses 8VSB standard.
QAM decoding is under development due to the variations in Cable service providers. QAM256 generally has been reported to work, although QAM64 still poses problems with the decoding software. FusionHDTV QAM decoding is limited to only the non-encrypted channels available (generally the OTA local stations).
64 QAM carries 27 Mbps of information.
256 QAM carries 40 Mbps.
CableCARD tuners have to be Bi-directiona CableCARD tuners can use VOD (video on demand), impulse PPV (Pay per view), and cable customized electronic program guide.
Home Theater and Hi Fidelity
PC Video Resolution - here, tdc.co.uk,
Multimedia Information Representation
See also: Video File Types
mov, qt QuickTime
WMV Windows Movie 750K/min.
AVI Microsoft Video Format
ASF Micorsoft Advanced Streaming Format
3GPP 3rd Generation Partnership Project for multimedia over 3rd gen. wireless.
VCD DAT, DivX, DV, IVF, DVD, VOB, XviD
Audio and Video in Web Publishing
See: Digital Video - Camcorder and Digital Video - Software and Digital Audio (MP3) players under Products.
Audio Video over the Web under networks/internet
DVI Tutorial - PacificCable.com.
See Audio Formats Above and Audio File Types.
8-VSB 8-level vestigial sideband - Modulation scheme for HDTV in the US
AC-3 - Active Coding-3 - 6 channel Dolby surround Anamorphic
Generally refers to the use of 16 x 9 aspect ratio pictures in a 4 x 3 system.
AAC - Advanced Audio Coding
ATSC Advanced Television Systems Committee ()
ATV - Advanced TV - Early name for DTV
CEMA - Consumer Electronics Manufacturers Association
DD Audio - Dolby Digital Audio
DTV - Digital TV (18 formats from SDTV to HDTV)
DVD - Digital Versatile Disk
DVI - Digital Visual Interface - Monitor interface with enough bandwidth for
uncompressed HD signals.
GA HDTV - Grand Alliance HDTV System (US standard)
HDMI™ - High-Definition Multimedia Interface.
HDMI is backward-compatible with most current DVI connections.
HDTV - High Definition TV
NTSC - National TV Standards Committee
PPV - Pay per view
QAM (digital cable tuners) - Quadrature Amplitude Modulation
YC or Y/C - (luminance And Chrominance) A video system widely used for production video
YUV - Also known as Y'CbCr and YPbPr) A production video system employing luminance
and two chroma components (red and blue)
SDTV - StanDard TV - The digital equivalent of the NTSC
RGB - Red,Green,Blue - Primary additive colors based on sensitivity of 3 pigments
in the cones in the retna of the human eye. (See: EE 498 at Wash. U.
VOD - video on demand
Glossaries at: HDTV Magazine, Crutchfield
video page for more
Audio Video in Networks/Internet
Video resolution standards
Video Resolution Notes
Projector Screens and Home Theater
HDTV - Flat Panel -
s-video vs. composite video vs. component video
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last updated 2 Jan 2007