Realtime
LYD-optagelse på Mac/PPC – og ud igen
Lydformater
Forberedelse
Programmer
Optagelse
Efterarbejde
Konvertering
Broadcast!
Gøre sine Real Audio-filer tilgængelige
Gøre sine Mp3-filer tilgængelige
Note:
Mp3 og RealAudio på 68K-Macintosh
Audio File
Formats FAQ (1995)
dden danske tekst © Kenneth Krabat
8. februar 2000
rev. 10. oktober 2000
LYDFORMATER
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Jeg er ikke teoretisk vidende om lydformater. Længere nede i dette dokument er en ældre FAQ over de enkelte formater – Audio File Formats FAQ – og dens hjemsted på nettet finder du hér.
En nyere finder du hér. Men jeg kan sige så meget, at
Mp3 er et komprimeret format, ca. 1:8/1:10 i forhold til originalen, med lille eller minimalt kvalitetstab. Kan streames*1+3 fra en server.
team-mp3.com har en glimrende teknisk FAQ om Mp3-formatet og hér en mere generel. Mp3rightnow.com har en masse programmer, information og links. Og hér er flere – dog mest til Windows (man kan jo klage…)
Real Audio er et komprimeret format, ca. 1:100 i forhold til originalen, hvis den skal kunne hentes og høres via et 28.8 modem, med et vist kvalitetstab, men kvaliteten kan hæves ved at sætte større krav til modtagerens modemhastighed. Kan streames*1.
AIFF er (så vidt jeg ved) ukomprimerede, og derfor kvalitetsmæssigt intakte.
QuickTime movies er et komprimeret format med lille eller ringe kvalitetstab.
Kan streames*1+2, men d.d. fungerer det ikke til Netscape på Macintosh. Filen kan dog downloades og høres efter download.
Ca. 1:10 i forhold til originalen.
Hér
kan du læse en lang udredning om de mest populære formater, deres fordele og ulemper både ved streaming af lyd og billede.
Der findes andre lydformater – .WAV, .au, system7 (til Mac) og MIDI ikke mindst – men ovenstående er at foretrække, hvis man vil dele med flest muligt og have flest programmer at vælge fra.
*1 Streaming
betyder både, at filen kan høres “fra serveren” uden at blive downloadet til klient-computeren (hvilket er smart, hvis man vil undgå at få sine lydfiler i omløb, som det er tilfældet med Mp3-filer) og at man kan “spole” i den komprimerede fil, præcis som på en CD. Forvirrende, men sådan er det.
*2 QuickTime-filer bliver downloadede.
*3 Dog kun i Mp1-formatet; kvaliteten er ikke så høj; sikkert som RealAudio
FORBEREDELSE
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Man åbner sit program og finder i dets indstillinger ud af, hvilken placering der bruges som scratchdisc – mellemlager – og derefter om der er plads på den pågældende
HD til den mængde lyd, man vil optage.
640Mb svarer til 74 minutter – det giver (mumle mumle) 8,6486486486 Mb lyd pr. minut. Det er nu ikke altid rigtigt, fordi 74 minutter er lig de 640 Mb på en CD, hvad enten det er stereo eller mono – men regn med 8.7 Mb i Stereo, og 5Mb i mono.
PROGRAMMER
til lydoptagelse
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Der er mange amatørprogrammer, man kan bruge til at optage med fra ekstern kilde (og mange professionelle, som kræver manual og stor lydteoretisk viden).
Her er et sted (Hitsquad), som rummer mange, mange programmer – dog ingen “payware”-programmer.
Gå direkte til Mac-siden eller til Audio converters til Mac
AIFF-filer
Coaster (v. 1.1.2 d.d. – det har den fordel, at man – når man har fundet indspillestyrken – kan optage fra en LP/CD/MC eller mikrofon, og så bare “klippe” efter hvert nummer; så får man en selvstændig lydfil for hvert nummer uden at skulle stoppe programmet. Det kræver dog at man sidder parat og kender sin plade rimelig godt)
FeltTip Sound Studio
– lille sharewareprogram med gode filtre – hjemmeside
SoundEdit 16
fra Macromedia (v 2.0.7 til brug for iMac/OS 8.5 + – stort program fra Macromedia, som har 50 effektfiltre til at lege lydmand med – med lidt øvelse kan man gøre det samme som ovenstående). Payware
SoundMaker (sidste version 1.0.3
– derefter ingen opdateringer; lille program med 100-vis af supergode og sjove effekt-, redigerings- og editeringsmuligheder; fungerer i princippet som SoundEdit, men er ikke helt så overskueligt. Men det er hurtigere end SE16)
Real Audio
RealProducer
(pt. v. 6 etellerandet – kan producere både god kvalitet RealAudiofiler og optage real-time til RealAudio-formatet fra extern indgang, CD eller mikrofon) – hjemmeside
Mp3
MPEG Audio Creator
(pt. v. 2.0 – er primært en hurtig AIFF->Mp3->AIFF-converter, men kan optage real-time til Mp2 – har dog ikke den store betydning for kvaliteten. Kræver dog, at maskinen understøtter 44Khz/16bit optagelse og har mindst en180MHz 604 processor eller 603/200MHz+. “Payware”
OPTAGELSE
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Man trækker en ledning fra sit stereonalægs båndoptagerudgang til Mac’ens mikrofon-indgang; en phono til minijack, hvis man har phono-udgang på stereoen. Man kan
også trække en ledning fra stereoanlæggets hovedtelefonudgangen, men så vær MEGET varsom med udgangsniveauet – og det er heller ikke altid, at det lyder godt, fordi dette signal er et forstærket signal (og så ved jeg ikke mere…)
Man åbner sit program, gør de nødvendige fagter for at få magien til at virke, og vupti… er man i gang med at optage (læs de medfølgende ReadMe-filer, men ovenfornævnte programmer er superenkle og ligetil).
Hvis man vil sikre sig, at filen har den optimale lydkvalitet, INDEN man konverter den til Mp3, RealAudio (eller et andet format), skal man optage den i CDkvalitet, dvs. 44 kHz/16bit. Jo højere frekvens og bit-rate, desto flere informationer = bedre lyd.
Hvis man vil optage flere lydfiler fra den samme kilde, og man ikke kan lave det hele i samme session, er det klogt at skrive ned hvad indstillingerne i program og evt. ekstern mixer står på; man kan også tage et screenshot af programmets indstillinger og gemme dette og evt. nedskrevne informationer i samme mappe som lydfilerne. Har man et godt øre, kan man evt. lave en referencefil, som holder dét niveau, man vil have – og så indstille niveau på den nye fil indtil den matcher afspilningsnuíveauet på
referencefilen.
EFTERARBEJDE
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Dette gælder “kun” AIFF-filer, og andre, “løst” komprimerede, lydformater; det er dog muligt at fikse “pops’n’cracks” på Mp3 filer, men programmer til dét formål findes vist endnu kun til Windows.
Med SoundEdit16 og SoundManager og mange sharewareprogrammer kan man efterbehandle lyden – dvs. stille niveau op og ned, equalize og lege sine numre sønder og sammen.
Anbefalede shareware-programmer listes gerne hér, hvis man skriver en kort forklaring
på sit elskede programs genialitet.
KONVERTERING
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AIFF->Mp3->AIFF:
MPEG
Audio Creator “for the latest versions of both encoder and player”
AudioCatalyst™ 2.0.0 – hurtig – hjemmeside
SoundJam – er også en udmærket Mp3-player – hjemmeside
SoundApp
2.7 – kan konvertere mellem alle lydformater, minimumssystemkrav 68020/OS7; SoundApp kræver dog en hurtig processor (200MHz+) for at afspille MPEG’formatet – hjemmeside
AIFF->RealAudio
RealProducer
– som ovenstående
RealAudio Encoder – ældre udgave af RealProducer, der ikke fylder så meget, er hurtig, men giver “knap” så gode RA-filer som den nyere udgave (OBS: den kan være svær at finde)
(Der findes programmer, ikke lavet af Real.com, sim kan producere RA-filer, men jeg kender dem ikke; fortæl mig gerne, hvis du ved noget eller finder ud af det – krabat@menneske.dk)
Real Audio->AIFF
Real Audio->Mp3
(jeg kender ikke nogen programmer, der kan gøre dette, men er MEGET interesseret!!)
BROADCAST!
For at man kan streame Mp3 eller RealAudio fra sin server eller sin desktop (sin egen computer) behøves programmer, der kan dén slags (…!). Mere følger senere, men tjeck foreløbig Icecast eller MacCast (Mp3), RealAudio (RealAudio)
Gøre Sine RealAudio-filer Tilgængelige
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Gå til realAudio’s site og indtast de relevante oplysninger
http://realguide.real.com/info/?page=submit
Gøre Sine Mp3-filer Tilgængelige
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Limewire, Macster, Carracho, Hotline
NOTE:
Mp3 og RealAudio på 68K-Macintosh
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For at en maskine kan afvikle disse hyperkomprimerede filer – læse dem fra harddiske, pakke dem ud og afvikle dem – behøver maskinen en FPU (Floating Point Processor); det er en matematisk co-processor, som assisterer CPU’en med at beregne – og CPU’ens hastighed og maskinens bushastighed skal også være af en vis størrelse.
REAL AUDIO
Jeg har testet en ældre model RealAudio Player (v. 3.0) sammen med en software FPU (SoftFPU 3.04) på en Performa 475/25MHz. Resultat var som følger
14.4 RealAudio-filer kunne godt afvikles, men lydkvaliteten var ikke noget at skrive hjem om. Og om man kunne høre dem streaming over nettet tvivler jeg på, da CPU’en da vil have rigeligt at gøre med at holde netforbindelse og browser kørende samtidig.
28.8 RealAudio-filer – nul putte
Min konklusion er, at maskinen skal op omkring 40-50MHz, før den kan afvikle en RealAudiofil af en tålelig kvalitet. Hvordan det ville forløbe med en hardwareFPU
på en 68K maskine kan jeg kun gætte om – men jeg formoder at det går; i dette tilfælde skal CPU’en ikke læse både lydfil og software FPU fra maskinen samtidig.
Mp3
Glem det.
Audio File Formats FAQ
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THIS IS AN OLD LIST – 1995, but apart from realAudio documentation, it kind of still stands.
SoundApp
supports many different file formats, but what exactly are they? The following
is a brief description of the various sound formats that SoundApp supports:
SoundCap:
This is a Macintosh sound format created for use with an early audio digitizer.
Version 4.3 of the application circa 1986 is the latest I’ve seen. It was
written by Mark Zimmer and Tom Hedges from Fractal Software. It supported
two basic flavors of sounds, compressed and uncompressed. Both types had ‘FSSD’
as the file type and ‘FSSC’ as the creator. Uncompressed files are just a
series of 8-bit unsigned bytes in the data fork. Compressed files store information
pertaining to sampling rate and a checksum. Sampling rates are limited to
5.6, 7.4, 11.1 and 22.2 kHz, and compression is done with a Huffman algorithm.
Compressed files are sometimes referred to as HCOM files because that is the
first four characters of the file.
SoundEdit:
This is the same file type as uncompressed SoundCap for mono sounds. In addition,
it adds to the resource fork some information about colors, labels, looping
segments and the format. The most useful for playback is the ‘INFO’ resource,
which stores the sampling rate, limited to the same four as SoundCap. Stereo
files consist of the left and right channels stored back-to-back in the data
fork. The ‘INFO’ resource specifies the lengths of each channel, which can
be different. SoundEdit came with the MacRecorder sound digitizer from Farallon
and later by MacroMedia. SoundEdit Pro and SoundEdit 16 are more recent incarnations,
and they support a much larger format suite, including up to 48-kHz samples
and 16-bit resolution. They shed the limitations inherent in the original
format. SoundApp does not currently support SoundEdit Pro or SoundEdit 16
files. (it does now – 2000/02)
Studio Session
Instrument: This format is primarily used with Super Studio Session and
stores digitally sampled instruments. There are two types: compressed and
uncompressed. Compressed instruments have the same format as compressed SoundCap
files, and uncompressed instruments are likewise similar to uncompressed SoundCap
files, with the addition of an eight-byte header.
AIFF
and AIFF-C: AIFF stands for Audio Interchange File Format and was developed
by Apple for storage of sounds in the data fork. It has been adopted by SGI
and some other specialized applications. The Macintosh OS includes support
for playing and creating AIFF files. More information about the format can
be found in Inside Macintosh VI or Inside Macintosh: Sound. In addition, the
format specification can be found at various places on the Internet. AIFF
is a very flexible file format, allowing the specification of arbitrary sampling
rates, sample size, number of channels, and application-specific format chunks
which can be ignored by other applications. AIFF-C is basically AIFF with
compressed samples. Apple supports two types of compression on the Macintosh,
MACE 3-to-1 and MACE 6-to-1. Both are lossy compression algorithms, but provide
reasonable quality with a great space savings. In addition, the Apple II GS
uses ACE 2-to-1 and ACE 8-to-3 compression, but SoundApp only supports MACE-compressed
files. Unlike SoundCap/Edit, samples are stored as two’s complement values.
Lossy compression means the compressed sound will not sound exactly like the
original sound, much like JPEGs do not look exactly like the original picture.
System 7
and ‘snd ‘: System 7 sound files are simply type 1 ‘snd ‘ resources
stored with a type of ‘sfil’ and a creator of ‘movr’. System 7 provides the
familiar icon for them and permits playback in the Finder by double-clicking
on them. A ‘snd ‘ is a type of resource which consists of a series of commands
for use by the Sound Manager. In addition to digitized sound samples, ‘snd
‘ resources can contain direct frequency-modulated and wave table-based sounds.
Any number of the three types can be combined with various effects to produce
complex sound files. Simple Beep is an example of a non-digitized ‘snd ‘.
There are two types of ‘snd ‘ resources, amazingly called type 1 and type
2. Type 1 is the format described above and is referred to as the System sound
format. Type 2 is for use with HyperCard and can contain only a sampled (digitized)
sound. SoundApp can play both types but will only convert sampled sounds.
For more information on ‘snd ‘ files consult Inside Macintosh VI or Inside
Macintosh: Sound. A familiarity with the Resource Manager would also be helpful.
8-bit samples are stored as unsigned bytes, like SoundCap/Edit, but 16-bit
samples are signed, like AIFF. Stereo ‘snd ‘ resources are also possible,
but Sound Manager 3.0 is required to play 16-bit samples directly. The two
types of compression for ‘snd ‘ resources are the same MACE types used in
AIFF files.
Sun Audio (.au)
and NeXT: Internally, these are the same formats. SoundApp differentiates
between them by file type or suffix merely for the user’s benefit. The format
specifies arbitrary sampling rates and multi-channel sounds. It supports a
number of sound encodings, including µ-law, a-law, various linear formats
of varying sample sizes, floating point samples, native DSP samples and G.72x
ADPCM compression. SoundApp supports µ-law, a-law, 8-bit signed, 16-bit
signed, G.721 ADPCM and both versions of G.723 ADPCM. Each µ-law sample
is stored in 8 bits, but the meaning of the sample is different. Normal sound
formats use a linear encoding, whereas µ-law and a-law are logarithmic.
This means that the spacing between the different sound levels grow progressively
larger as the values increase. This format provides a larger dynamic range
than normal 8-bit samples, approximately equivalent to 12-bit samples. However,
it suffers from more noise than linear encodings. The G.721, G.723-24 and
G.723-40 ADPCM formats are CCITT standards for compression of 8000-Hz 14-bit
samples into a 32-, 24- or 40-kbps data stream. These compressed formats are
not very popular due to the extremely slow decompression rates. Most files
start with the four-character signature, ‘.snd’, but there are some older
headerless AU files. These are assumed to be µ-law encoded, mono at 8000
Hz. A “.al” suffix will force the sound to be a-law, if it does not have a
header. The U.S. telephone system uses µ-law encoding for digitization,
whereas the European telephone systems use a-law encoding.
PSION
sound file: This format consists of a short header followed by a-law encoded
samples at 8000 Hz. It is used by the PSION Series 3 palmtop personal information
manager and uses a “.WVE” suffix.
Windows WAVE:
This format was created by Microsoft and IBM, and it has unfortunately become
a popular standard. Like AU, it specifies an arbitrary sampling rate, number
of channels and sample size. It also specifies a number of application-specific
blocks within the file. It has a plethora of different compression formats,
although the Microsoft ADPCM is the most popular. SoundApp only supports 8-,
16-bit and MS ADPCM-compressed sounds. MS ADPCM provides 4-to-1 compression.
All data fields and 16-bit samples are stored in little-endian notation, as
Intel processors require. All other formats supported by SoundApp use big-endian
notation which means the high-bytes come first in the data stream.
Sound Blaster
VOC: This is the format used by the Creative Voice SoundBlaster hardware
used in IBM-compatible computers and is optimized for that hardware. It specifies
sampling rate as a multiple of an internal clock and is not as flexible as
the other general formats. Data can be segmented and portions of silence can
be added. SoundApp supports both of these features, but not the looping feature.
Amiga IFF (8SVX):
This is the dominant format on the Commodore Amiga platform. It can specify
an arbitray sampling rate but ony supports mono 8-bit sounds. It also supports
a 2-to-1 lossy compression format which uses a unique Fibonacci delta compression.
Sound Designer
II (SDII): This is a format for professional sound editing on the Macintosh.
It can specify arbitrary sampling rates and supports multiple channels and
data sizes. Information regarding the specifics of the sound are stored in
three ‘STR ‘ resources. Like VOC, 8SVX and WAVE, samples are encoded as signed
values. More information about this format can be obtained from Digidesign.
SoundApp only supports version II files.
DVI ADPCM:
This is the Intel/DVI ADPCM (Adaptave Differential Pulse Code Modulation)
format. It is a 4-to-1 compressed 16-bit file format. It is unique among the
various ADPCM formats in that it’s very fast, and like all ADPCM formats it
is lossy. The version of the format that SoundApp supports plays at a 8000-Hz
sampling rate.
Amiga MOD:
This is not really a sound format but a music format. It stores digitized
instruments and contains a musical score which produces a lengthy composition
with a very small amount of data. There have been various extensions to this
format, but SoundApp only supports those which Sound Trecker 2.2 supports.
These include Amiga SoundTracker, StarTracker, NoiseTracker, ProTracker (4-track),
Amiga StarTracker (4- and 8-track), Oktalyzer (4-8 track), Amiga MED/OctaMED
(4-16 track MMD0/1/2 formats), IBM FastTracker (4-, 6- and 8-track), IBM TakeTracker
(1-32 track). SoundApp does not support MTM or S3M formats. Native code will
be used for MOD playback on a Power Macintosh.
QuickTime
Movies: This is the Apple standard for time-based multimedia files. Versions
1.x support moving pictures, sound and later versions support text. QuickTime
2.0 supports MIDI tracks; however, conversion of MIDI data to other sound
formats is not supported by QuickTime 2.0. QuickTime 2.0 or later and the
QuickTime Musical Instruments extension must be installed in order to play
QuickTime MIDI files. It is highly advisable to install the Apple Multimedia
Tuner version 2.0.1 or later as well. This extension is freely available from
Apple’s online support services and makes QuickTime and Sound Manager 3.0
memory management considerably more robust.
MIDI:
Musical Instrument Digitial Interface is primarily a standard for communication
between musical instruments. General MIDI is a standard for storing compositions
based on what events happened during the performance. It does not contain
digitized audio data; instead, it stores only the information about which
notes were played in a time-line format. This is similar to the MOD format
but without the digitized instrument samples. QuickTime 2.0 or later supports
General MIDI data in QuickTime movies. In order to listen to MIDI files with
SoundApp, they must first be converted to QuickTime files. This can be done
via the Import QuickTime menu item in the File menu.
Audio CD
Tracks: A lot of programs can “rip” CD’s – and the format is
AIFF. Audio tracks take up a huge amount of space.
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