basic audio glossary

There’s lots of jargon when it comes to talking about sound and sound equipment…there’s also been a LOT of mis-use of the audio terms, so I’ve decided to put together a few of the words used by us audio geeks and explain them in layman’s terms so that when you go looking for some gear for your home theater or for your band, you know what’s going on.  I did NOT place these terms in alphabetical order, but placed them in the most commonly used order!

BASS:  This is low frequency sound…In large quantities, it shakes the floor and shakes you too!  For you music people, it’s the keys on the left hand side of the piano or keyboard.  Bass requires big speakers called woofers and big power to generate.  Drums produce bass, and the larger the drum, the lower the frequency, and deeper the bass.  Bass seems to be about the only thing teenagers with small Japanese cars tend think about when they purchase a stereo, especially when they drive by your house.  Bass adds impact to movie soundtracks and makes things like explosions and crashes more dramatic.

TREBLE:  Is high frequency sound.  We are talking birds chirping, squeaky shopping cart wheels, It is produced by small speakers called tweeters that are frequency enhanced with horns to help disperse and amplify it.  For your music makers, treble is the right hand side of the keyboard.  Instruments like cymbals, triangles, and piccolos all produce treble.  Many instruments that also produce other frequencies of sound however also produce some secondary high treble sounds like violins and other string instruments.  There’s also lots of treble sounds created naturally.   For nice, lifelike sound, it’s good to have plenty of treble in your sound system as well.

MIDRANGE:  Many people neglect midrange sound, but is also important.  Midrange sound is all the stuff that is in between bass and treble.  It’s what our ears hear most clearly, and what they are most sensitive to.  Midrange is the sound frequencies where most human speech is at.  Most musical instruments also produce midrange tones as their primary sounds.  If a sound system is for human speech, like a public address system, it must reproduce midrange cleanly and with low distortion so we can interpret what is being said clearly.

DYNAMIC RANGE:  Many people speak of dynamic range as the ability to produce both bass and treble at the same time, but this is NOT what dynamic range is!  Dynamic range is the difference between loud and quiet.  We have all experienced those loud commercials that come on after a quiet TV show…this is dynamic range.  Suprisingly, music that sounds more dramatic, powerful and loud is not necessarily louder than other music.  The reason it sounds louder is because there are quieter parts to it too that you compare the loud parts to.  This music has a wide dynamic range, or simply put, it is dynamic.

SIGNAL TO NOISE: Have you ever had a hard time listening to someone that is right beside you speaking at a loud party or concert?  The reason why you cannot understand them is because other sound that you do not want to hear is drowning out the sound you desire to hear.  This could be referred to as a bad or low signal to noise ratio. Another good example is if you are listening to the radio in town.  At this point, signal to noise is good, and you can hear the station well.  Once you drive out of town though, the radio station fades out, and the static eventually overcomes the station as the signal (the radio station)to noise (static) ratio gets lower or worse.  Signal to noise ratio is similar to dynamic range.  Good signal to noise ratios means you can produce lots of dynamic range because your quiet parts don’t washed out under background noise produced by poor sound equipment.

DISTORTION:  Distortion is actually rather simple to explain.  It is any change in the sound from the way it was originally.  The goal of a sound system is to reproduce sound with as little distortion, or changes to the sound as possible as the sound travels through it.  Distortion is produced for a number of reasons.  One of the most common is when a piece of sound equipment is asked to produce a sound that is louder than it actually can.  The sound wave will be “clipped” and it becomes dull and hard to understand.  Think of the little speaker at the fast food drive-thru and how different it sounds from when you speak to the clerk directly.

Distortion is normally undesirable, but it can be used creatively when making music however.  “Fuzzboxes”, and “overdrives” are frequently used in guitars and other instruments to purposefully generate distortion.   The distortion generated is full of overtones and other sound frequencies that makes for a richer, fuller sound.

DECIBEL:  This is a unit of measurement for sound.  You may see decibel numbers describing sound equipment and all sorts of measurements.  Here’s a good reference for you. The quiet woodlands is about 30db. A typical conversation is about 60 decibels.  Machinery, appliances and traffic, about 90 decibels,  a rock concert about 120 db, and a jet plane taking off about 150 decibels.   Human hearing can be damaged at levels above 90 to 100 decibels.

Decibels can be used for describing signal to noise too.  A signal to noise ratio of about 60 decibels is typical of a cassette tape, while a CD player is capable of signal to noise ratios of about 90 decibels.  Okay, so what does that mean?   Well, it means the range of how quiet something can be recorded before it gets washed out in background noise.  If a sound at 90 decibels is recorded onto a cassette tape, like a guitar  the background noise will be 60 decibels quieter than that sound.  If a quiet sound, like a person’s whisper would be recorded to the same tape, you would probably not be able to hear it above the background hiss of the tape.  In order to record the whisper, the recording volume would need to be turned up to record the whisper, then back down to record the guitar.  A CD however, would be able to record both of the sounds without adjusting.

COMPRESSION:  This is a method of purposefully reducing dynamic range.   Compression is sort of like adjusting the volume control up and down.  Think about that TV show again.  What do you do during the quiet TV show?  Chances are, you turn up the volume.  Then, what happens when the loud commercial comes on?  Well, you turn the volume back down!  You have just performed a simple form of dynamic range compression so that the sound you are listening to is at the same volume despite the varying loudness.

There is actually a sound device called a compressor that performs this automatically.  Compressing sound may sound like a bad thing because it reduces dynamic range, but sometimes it is necessary, like to reduce distortion.  Compression is useful in a pubic address system where one person speaking my have a quiet voice, and the next person speaking has a loud voice.  You could have a sound technician on-site to adjust the level, or just have a compressor automatically do it for you.  Remember the cassette tape example above?  Well, a compressor could be used to bring the whisper up loud enough, and bring the guitar down low enough so that both sounds can be recorded onto the tape without adjusting the level controls.

Now, you probably now have a little bit of confusion when it comes to compression.  Chances are you have heard about compression when talking about MP3 tracks and digital music, but this is something totally different. This is called digital compression. Digital compression removes sound and creates distortion so that the file size is smaller for transfer over the internet and storage on hard drives…but more on that later!

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