BIG Audio Book Blow Out

So you want to learn how to use a compressor? Well good luck. It takes years to get even a decent feel for a compressor. I’m just now getting where I feel that a compressor will tolerate me playing with it’s settings. In the past, it was just laughing and mocking me because I just didn’t understand how to use it to improve my recordings.

So let’s talk about how a compressor can make an audio tracker louder. Ironically, a compressor actually knocks the volume down on a track, but then has a makeup gain knob that boosts it back up. To understand how a compressor can make something louder, you need to understand the difference between peak loudness and average loudness (also called RMS). A peak is just what it says it is. It’s a spike. The signal starts very low and goes very high. A good example of peak loudness is a snare drum hit. Average loudness is sound that occurs over time. Imagine hitting a low E on a bass guitar and letting it sustain. This is an almost constant sound.

One other concept is the volume ceiling. In other words, in digital audio we have a volume limit. It’s called zero. For whatever reason they measure volume in negative numbers with 0dB being the absolute loudest. If a track has a peak that jumps up to zero, we can not push the volume up on that track even if the other portions of the track are very low in volume (without volume automation).

Now let’s take an audio track that can be both peaky and constant. A vocal track is a great example. A vocal can jump up very quickly but it can also sustain. Let’s say it hits 0db at one point, but most of the track is sitting well below that. You’ll find that when the vocal is set at maximum gain before clipping, the many of the words are unintelligible. This is because they are simply too quite. Assuming there are no extreme problems, the first thing I’ll usually do is grab a compressor. I’m go ahead and smash those peaks down and then I’ll push the volume back up with the make up gain on the compressor. Now the vocal is evened up quite a bit. The vocal will sit in the track much better and will sound fuller.

When mastering a record, compression is almost always used to make the volume of the cd louder. Most of the time, the cd is already hitting zero, so it’s peak volume will not increase. However, it’s RMS or average volume can increase substantially. When we put a compressor on stereo mix, we can smash the song down into a smaller dynamic range. It uses up less volume. While this can be a bad thing as the dynamics are decreased, these days overall volume seams to be more important (I’m not sure who decided this). After the compressor does it’s thing, the makeup gain is used to boost the level of the track up the desired amount.

When you are learning the audio mixing process, I recommend using more compression than you think you need. Hit everything very hard. If it sounds distorted, back off. I think that compression is the opposite of reverb. While many beginning home recording enthusiasts will use too much reverb, they often times, do not use as much compression as the big boys. Experiment. This is different for everyone.

In summary, a compressor is used to to knock off the top (loudest parts) of an audio signal and then uses it’s makeup gain to push the volume back up. It takes lots of time to master using a compressor. Keep in mind that you can do much more with a compressor than make things louder. As always, don’t be afraid to experiment.

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FILE FORMATS

There are several audio file formats in common use. There are fewer video file formats, but audio video file extensions can be confusing. This is just a brief description of what the more commonly used audio and video file formats and systems are.

AAC:Advanced Audio Coding This is the audio file format used by Apple for the iTunes Music Store, and it may appear with the M4A filename extension. It is better than MP3 for sound quality. It was developed as part of the MPEG4 group owned by Dolby (see below).

AU: This audio file format is the standard used by Java, Sun and Unix.

MPEG: Moving Pictures Expert Group There are a number of MPEG types now, described below.

MPEG-1: This is used in digital cameras and camcorders for small video clips. VHS quality playback can be expected from MPEG-1.

MPEG-2: Used for digital satellite TV, professional movie recording and recording of home DVD recordings. Provides provision for multi-channel surround sound recordings.

MPEG-3: MPEG-3 was propose as an entity, but eventually merged into MPEG-2.

MPEG-4: This is the newest MPEG system and is used for streaming internet content. It is also used in portable video recorders and for internet downloads. Required for DivX. It improves digital broadcasting and interactive graphics and multimedia.

MP3: Digital audio files, most commonly used to store and playback music. It compresses the files to about 10% of a normal audio file, and a normal music track will be about 5 -6 MB in size. MP3 stands for MPEG-1 Audio Layer 3, not MPEG-3 as many people think. A typical MP3 audio file is near CD quality.

OGG: An audio file format supporting a variety of codecs, the most popular of which is the audio codec Vorbis. However, MP3 files are much more broadly supported than Vorbis.

RA: Real Audio This format is designed for streaming audio over the Internet. It is a self-contained file format with all the audio information stored within the file itself.

WAV: The simplest of the audio file formats, developed by Microsoft and IBM, and built into Windows 95. It is an uncompressed audio file format with large file sizes (10 x MP3), and does not need further processing to play. The WAV file consists of three blocks of information: The RIFF block which identifies the file as a WAV file, The FORMAT block which identifies parameters such as sample rate and the DATA block which contains the actual data, or music sample.

WMA: Windows Media Audio A digital system invented by Microsoft, and is used in portable digital audio players. Using WMA, a file can be programmed so that it cannot be copied, and can be used to protect copyright.

WMF: Windows Media Format These are audio-video files comprising WMA and video codecs. They provide high quality and media security for streaming and download and play applications on computers.

WMV: Windows Media Video Used in the Windows media Player, this is used to stream and download and play audio and video content.

When dealing with audio and video file formats, you will sometimes notice the term ‘codec’. A codec is simply short for encoder-decoder (or compressor - decompressor). A main function of a codec is to compress audio or video data streams so that transmission of digital audio samples and video frames can be speeded up and storage space reduced.

The objective of all codecs is to reduce the file size to a minimum while maintaining audio and video quality. A quick indication of the codec’s place in the path of transmission and reception is:

Video device (e.g. camcorder) - video capture card - video digitized - codec (compresses digital info) - result (MPEG2, AVI, WMV etc) - codec (decompress) - video frames - display device.

Between the two codecs the compressed result is transferred to the display device transmitted, stored on file, etc). So to condense the flow even further, we could basically describe it as:

raw data - codec - transmit - codec - play

This is simplistic, but it shows where the codecs are used. Therefore, in order to play a movie, video or piece of music of a certain format, you need a codec in your computer to allow you to decompress the file and play it.

Here is some free software which checks what codec a video system uses, and what codec your system needs to play it:

Codec Tool.

The different video file formats are required to meet the requirements of various video devices. Similarly, audio file formats are designed to meet the needs of the specific delivery methods and storage and playback devices introduced by large corporations such as Microsoft, Sony and Apple. Thus, Sony invented the UMD (Universal Media Disk) for the PSP (Playstation Portable), and Apple introduced AAC (M4A) for its iPod.

Peter Nisbet is the author of many articles on audio and video file systems, their transmission, playback and conversion. More information is available on his websites http://www.legalandfree.com and http://www.online-free-movies.com

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Oh, hi. Excuse me while I take off these headphones. I was just away in Key West, listening to Van Morrison’s “Brown Eyed Girl” on the radio.

Actually, my body was sitting here in my home in North Carolina. But I decided it would be neat to listen to a Key West station while imagining the tourists congregating for the famous sunset-watching ritual. Who knows, some of them might be standing there listening to the very same radio station while gazing at that big orange fireball sinking beneath the horizon.

I found the live streaming audio of that Key West radio station on Mike’s Radio World (www.mikesradio.com), perhaps the least flashy yet most useful radio guide Web site I have yet to come across.

“Mike” is Mike Dean, according to the scanty information available, and beyond that there’s not much about him. His site is frankly amateurish looking, with layout and (minimal) graphics that appear to be straight out of the 1990s. (Based on the visitor counter displayed there, the site has existed at least since May, 2001.)

Despite such “deficiencies”–or perhaps because of them–Mike’s Radio World is an excellent resource for those looking for live Internet radio streams from around the world. It’s simple, straightforward and to the point without frills or fluff–not even any ads that I can see.

Mike’s Radio World calls itself “Your global Internet radio guide,” and with good reason. It contains links to more than 3,000 live radio streams, categorized by genre and then again by world region, followed by the country. The listing for each station includes two links, one to the station’s Web site and the other to the live audio stream. If the user happens not to have the correct media player software on his or her system to play a particular stream, Mike has conveniently included a button for downloading it.

You could spend a lot of time roaming the world on this site and never listen to more than a fraction of the radio stations that are included in the 3,000+ directory. It would be fun to try, though.

Mike’s Radio World is a throwback to the days when enthusiastic amateurs created Web sites on their favorite topics for the sheer love it, and not with the idea that they would make a ton of money from it. It does one thing and does it exceptionally well–provides a well-organized, easily navigable collection of live links to live radio streams for the radio junkies of the world.

Thank you, Mike!

Stefan Smith is a radio and music junkie who writes on these and other subjects for the Solid Gold Info Writers Consortium. Recently, he has written an extensive review of new software that anyone can use to capture music audio streams from Internet radio broadcasts and break them up into individual mp3 song files–a legal way to download virtually free music. Read the review at: http://www.solid-gold.info/radio2mp3.html

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