High Level basics about tape decks and players

Prior to CDs there cassette tapes were and still are very popular. The evolution of these tapes is simplistic while complex. Cassette tapes and decks are the descendants of reel to reel. Reel to Reel tapes were like the big movie reels with a full and open spindle. You threaded the tape through the mechanism and feed it into the empty reel. The device had two head, one to record and another for play back. Once you recorded the information from your selected source you rewind it and played it back. Somewhere alone the line a bright person came up with the idea of creating a small self contained carrier to house the reels and a device that plays these tapes. 

Their innovation lead to the creation of what we call the modern cassette tape and tape deck. Like the reel to reel a cassette player recorder has two heads (record/play). Unlike the reel to reel the cassette tape ahs a mechanism that self threads the tape for both payback and record and the housing has tapes to allow you to prevent the tape from being written over one recorded. 

In a cassette tape the reels are called spools and they are notched to fit over motors that advance and rewind them. In a stereo cassette there are 4 tracks – two per channel. Philips introduced the compact audio cassette medium for audio storage in Europe in 1963, and in the United States in 1964, under the trademark name Compact Cassette. 

Cassette tapes are made of a polyester type plastic film with a magnetic coating. Because this is a mechanical system it is subject to the limitation of wear and degradation with age. Excessive exposure to heat and like also degrade this tapes. Over time with the advent of technology these cassettes eventually became able to record and reproduce the full range of human hearing and beyond. Also because the playback and record head are mechanical they need to be cleaned to remove the excesses dust, dirt and magnetic material that deposits on the respective heads. 

Typically a cassette deck player/recorder has the following controls eject, playback, forward, rewind, play, pause and stop. Additionally VU meters are employed to monitor signal levels and other controls exist to correct for balance, and on high end systems equalization and noise reduction like Dolby. 

The successors to the cassette tape are the DAT (Digital Audio Tape), MiniDisc, CD, and Flash drives.  

Trivia:

• Did you know the original purpose of these tapes was dictation?
• Did you know that the early home answer machines used endless loop tapes?
• Did you know the intermediate stage of was the 8 Track tape?
• Did you know that some of the early PCs used cassette tapes to record data?

 

High level basics about CDs and CD players

CD – Compact Disc

 

• CD-RW (Read/Write) is a rewritable format
• CD-R (Read) is a write one time only 

Most CDs come can hold anywhere between as 650 and 700 MB of data. 

A prerecorded compact disc has its information permanently written onto its surface while a CD-RW disc contains a phase-change alloy recording layer. 

CD-RWs are not as reliable for long-term storage; however, under recommended storage conditions, CD-RW should have a life expectancy of 25 years or more (as compared to 30+ years for CD-R). 

CD Player - a digital device that reads plastic disc which has notches etched under the surface that a laser reads and translates the signal back into audio which is eventually sent to the amplifier then speakers. Some modern CD players also can play MP 3 formatted information. A CD player has three major components: a drive motor, a lens system, and a tracking mechanism.

 

·        Did you know DVD players can play CDs?

·        Did you know that some CD players can also record?  

Want to learn more:

• http://www.cdrfaq.org/
  
• http://www.osta.org/technology/cdqa.htm
  

High level basics about EQ (Equalization)

Equalization – what is it? 

In basic terms it is a way to compensate for deficiencies in an audio signal. Many make the mistake of using to overcompensate instead of flattening the signal so that there are no bias (I will elaborate more later). 

You have seen these devices even in your windows media player. To the far right they control low, middle voice and other tones in this range, left symbols and other high pitched sounds.  In Technical terms it is defines as the process of changing the frequency envelope of a sound in audio processing. 

To quote Wikipedia – “The term "equalizer" is often incorrectly applied to audio filters, such as those included on DJ mixing equipment and hi-fi audio components. However, these "equalizers" are typically general all-purpose audio filters, which can be arranged to produce the effect of low pass, high pass, band pass and band stop filters. Such filters are true equalizers only when arranged to reverse the effects of internal circuitry on sound output. 

In Multitrack recording and sound reinforcement systems, individual channels have equalization for aesthetic reasons, while the combined mix of sound is processed through equalization for practical reasons. Any acoustic space will cause some sound frequencies to be louder than others. This is due to standing waves produced by the size of the room and the materials in it. Equalization is used to compensate for the discrepancies of a room's acoustics.” 

A graphic equalizer gets its name because of the graphic representation of the intensity of each frquency level. 

Typically in a well designed system once it is installed a spectrum analyzer is used in concert with a graphic equalizer to adjust the equipment and compensate for the acoustics of a room and make sure the signal is flat. Allow me to explain in some non technical detail. When a system is configured to have a flat frequency response it means there are no biases and no signal augmentations. As a result in an ideally designed system you could use a proper microphone and then record a song or vocalist and then when you play back the recorded sound it will sound exactly the same as the live performer or instruments.

Trivia: 

At a live event, where microphones and speakers operate simultaneously equalizers are used to ensure that there are no frequency bands where there is a round trip gain of greater than 1 to avoid feedback. Also all audio records, or vinyls, have had equalization applied to before the consumers' record was made because of the limitations of equipment.

High level basics about Audio Tuners

Many people enjoy listening to the radio. They do so either in their car or at home. And even now over the internet. 

An audio tuner is what makes that possible. Typically for the home (or business) these tuners pick up either AM or FM waves from the broadcaster. An internal processor interprets these waves, converts them to a signal which is eventually sent to the speakers and reproduced as the sound you hear coming from either your speakers or head phones. 

In technical terms - A tuner is a circuit module or free-standing equipment which detects radio-frequency (RF) signals usually of low amplitude and amplifies them and converts them to a form suitable for further processing. The signals being detected are usually electromagnetic waves 

Traditionally there were:

• AM - Low band uses amplitude modulation (0.300 MHz to 3 MHz)
  
• FM – High Band uses frequency modulation (30 MHz to 300 MHz)  
  

With the advent of satellites and digital technology – new bands and hence new receivers were developed these use 2.3 GHz S band (2.310 to 2.360 GHz) in the US companies like Sirius XM Radio use this. 

Trivia:

As of August 2007, the FCC (Federal Communications Commission) had licensed 4779 AM stations and 9159 FM stations (6279 commercial and 2880 educational).

High level basics about Sound Boards (Mixing Console)

This picture is of a sound system install we did at a church.

A sound board is a mixer as was discussed in previous post with the ability to enhance or augment the source signal(s). You can find these devices commonly used in  recording studios, public address systems, sound reinforcement systems, broadcasting,  and television studios among other things.

If you have ever wondered how the level of a singer or speaker is controlled and that of the live or prerecorded accompanist this device is how.  When used for live performances, the signal from the board is typically not sent for post processing rather it is sent straight to the amplifier (unless it is a powered sound board) meaning the amplifier is built in.

The board is usually divided into these sections:

• Channel Gain
• Input Jacks / Microphone preamps
• Basic input controls
• Channel EQ (High, Mids and low)
• Routing Section including Direct Outs, Aux-sends, Panning control and Subgroup assignments
• Input Faders
• Channel monitor level
• Subgroup faders
• Output controls including Master level controls, EQ and/or Matrix routing

As you can see from picture these are often color coded consistently (there is that word again) across each channel to make their purpose east to identify. Each channel typically has most of these controls to allow the operator the ability to uniquely tailor the various levels. An example using the above is the system speakers receive all output from all channels but the monitors (near the organist and the choir) have been set so that the choir does not hear themselves while they are singing.  Additionally in many newer systems a channel that is used typically by a single person can be set for level once and a single push button used to make the channel live or kill it.

The input controls (pots) are typically rotary knobs with marks around them denoting relative level of intensity. The input serves to buffer the signal and reduce the amount of extra noise in the system noise

Each channel typically also have basic equalization (Bass, mid low, mid high, and treble) Some systems also have Parametric equalization to allow the control internal band-pass filter sections (amplitude, center frequency and bandwidth)  

Subgroup and main output fader controls typically on the right side of the mixer (that is right since most people are right handed the boards are typically designed to accommodate right handed people)

Sounds boards also have VU (Volume Unit) or peak meters to monitor output levels for each channel or for some smaller boards just the master outputs to help reduce source and output signal over driving (also known as overmodulating or clipping). 

High level basics about Mixers and Source selectors

A mixer is a device that selects two our more line level source signals and combines them into a composite signal.   

A mixer should not be confused with a source selector it is similar to a mixer but it is in some cases integrated with the amplifier and in other cases the signal selector, amplifier, and tuner are combined in one unit. The signal selector is capable in some cases of mixing multiple sources however it is typically used to select a single source and routing that signal to an integrated or peripheral device like a tape deck or the amplifier. 

Mixers come in a variety of flavors however to keep this simple additive mixers combine two or more signals into a composite output that has the frequencies of both. It should be understood that with all electronics some resistance is present so their will be some subtle signal degradation. 

Type of mixers:

• Passive - resistor based
• Active – which do impedance matching and better isolation 

A sound board is a classic example of a mixer that most people are familiar with and they come with 8, 16, 32, etc channels which can all be combined. My next post will deal with sound boards in more detail.

High level basics about Amplifiers

The purpose of an amplifier is to take an analogue or digital audio signal sent at line level and raise its amplitude then send it to the speakers to reproduce the live or recorded sound. 

An amplifier reproduces the sound exactly as it receives it (more or less) since it is not a perfect reproduction some distortion is added on top of the distortion that may or may not exist in the source signal. The level of increase is determined by controls on the device and is usually scaled from 0 – 100 incrementally. 

Some items of interest with regards to amps are:

• Gain - the ratio of output to input power
• Bandwidth – The range of frequencies the amplifier can successfully transmit
• Efficiency – the measure of how much energy is converted to useful sound
• Noise - Noise Factor is the ratio of Signal to Noise Ratio of input signal to that of the output signal
• Slew rate - the maximum rate of change of output variable
• Overhead – the amount in reserve over the min required by speakers 

The mistake many make is confusing loudness with sound quality – just because a system is loud does not mean the sound is good. Allow me to give you a simple rule of thumb is the bigger the speaker the more power needed to move it. 

Think about it this way

• Pick up a pebble – how much effort does it take?
• Now try to pick up a bolder – much harder right? 

Each speaker makes sound by moving its diaphragms to create sounds waves by moving are, the large the speaker the more are that must be displaced and the more power needed. That is why speakers typically come with ratings to let you know the min required to make then function at an acceptable sound level. And yet overdrive (drive speakers to hard) they try to move air faster than they are designed and this causes distortion in the quality of sound. 

Here is a bit of trivia – did you know a microphone is a form of amplifier?

High level basics about speakers

The devil is in the details. Allow me to put a new slant on this truth – without details (standards) technology would not be possible. Things people take for granted would not work. Imagine speaker wire – if there were no standards then one person might use copper and another arbitrarily may use plastic – do you think the speakers will work in the second system? As important is the gauge (size) of the wire because if you use the wrong size the wire may overheat and you have a different problem short or possibly even a fire. 

The next few posts will deal the audio technology. Let’s start with speakers. The purpose of speakers is to reproduce sounds from live or prerecorded media. Depending on what you are trying to listen to and the speakers you are using the amplifier must be specified at a level to properly drive the speakers. 

The average human’s normal hearing range is approximately 20Hz - 20,000Hz. There are also many brands and often people look at the brands and are attracted by the name not paying attention to the technical details. There are various types of speakers each with a full range and each with its respective strengths and weakness. Let’s cover speaker technology with a broad brush. 

Enclosure types

• Metal
• Wood (custom or hand made and engineered)
• Ported (tuned to a certain bass (low) frequencies)
• Passive Radiator (a speaker with no driver that

Design types

• Equalized – attempt to balance behavior of each speaker’s performance in enclosure
• None Equalized 

Speaker purposes

• Full range – limited response attempting to replicate highs, mids and lows (typically uses a composite design with a whizzer cone to augment high sounds) but has higher distortion rate then others
• Tweeter – reproduces high frequencies – think symbols, snares – typically 2,000Hz – 20,000Hz
• Mid range – reproduces mid range – think tenor sax and human voice – typically 300Hz – 5000Hz
• Woofer – reproduces low range (bass) – think kick drum, engine rumble, low human voice  – typically 40Hz – 1000Hz 
• Sub Woofer –  Low low Bass (sounds more felt then heard) – typically 20Hz – 150Hz 

And there are crossovers, that these are devices that route certain frequencies to certain speakers (Bass frequencies to woofers and high frequencies to tweeters)

Speaker types:

•   Cone
  
•   Dome
  
•   Piezo electric
  
•   Ribbon
  
•   Planar-magnetic
  
•   Electrostatic
  
•   AMT
  
•  Horn
  
•  Plasma/Ion tweeter 

So how does a speaker work?

• The amplifier sends an electrical signal to driver element move and control a diaphragm (speaker) who shape, size and material determines the frequency of the sound made.
  

Image source

Audio Design

So you want a new sound system because you never had one or the old one no longer serves its purpose or you need to expand or just maybe the one you have is obsolete or never adequetly served your needs.

Often I have seen many sales people who instead of listening to the client pushes a product line. Fact is just because you see what appears to be an imposing system downs not mean it is or was the best system for you. When designing an audio system there are many things to take into account 

Sometimes some of the best sounding systems are those systems you cannot visually detect. Each system, amp and speakers have their inherent strengths and weaknesses. Also what type of system are you doing to use. Did you know a system designed to accurately reproduce a human voice is not the same as one to recreate music but one that is specified to do both offers the most flexibility and yet depending on what it is going to be used for (say a church sanctuary) is overkill. 

• Acoustics - study of sound
• Aesthetics - study of sensory or sensori-emotional values
• Reverberation - persistence of sound
• Tonal reproduction
• System use
• And many other factors. 

Next time you decide you want a system make sure the company is listening to your needs and working to supply a system that is as pleasing to look at as it is to hear.