Frequently Asked Questions in Hi-Fi Audio-Video

General

What is an analog signal?
An analog signal is an electromagnetic signal which varies continuously over time. An analog signal may assume any value within a given range of values.

What is a digital signal?
A digital signal is a signal which may assume only a discrete range of values over time. For example, a computer's program code must be a stream consisting of either 0s or 1s.

What is a balanced circuit?
A balanced circuit is one in which the positive polarity signal (the "hot" signal) and the negative polarity signal (the "cold" signal) are separated from the ground. When these signals are finally added together, any noise common to both signals is eliminated and the resulting signal is twice the level of either signal individually.

Do interconnects and speaker cables really make a difference?
Simply said, yes. Different cables transmit signals differently. But you might say, well, cable is cable, wire is wire - what's the difference. While every cable designer has his or her own theories about their own design, several factors are always present. Every cable has a certain impedance, a combination of the electrical characteristics of resistance, capacitance, and inductance. This impedance causes different component interaction and will effect the system sound quality. A cable's shielding or overall ability to reject extraneous environmental noise such as radio frequencies, will change its sound quality too.

How much should I spend on each component in my system?
There are no preset percentages which can be attributed to each component in your A/V system. The key to any high quality system is balance. By spending wisely and not allotting an overly large portion of your budget on any one component you will end up with a good system for your money. Always keep in mind the garbage in, garbage out principle, which can be applied to any component in your system. If one component in your system is far exceeded in quality by every other component, your overall system will suffer. Also remember to allocate money for quality cables, since the purest signals can be significantly degraded with poor speaker cables and interconnects.

What considerations should I make when buying a component?
Your primary consideration should always be sound and/or picture quality. This is not the only factor in the decision however. Of course your budget for the component must be taken into consideration. Remember that good quality components can be found in almost any price range. Build quality and reliability are other issues. While this may not be immediately apparent, often looking thoroughly at a component will give some indication of its construction quality. Ask around about this as well. How well the component will interact with your other existing components is very important. Just because a piece sounds incredible in one system does not always guarantee its performance in your own system. If you can try the component in your system, take advantage of this opportunity. If this is not an option, ask someone with greater experience about his or her opinion regarding how well it will work in your system. These elements should help to guide you to a better component purchase.

Television

How does a television work?
When a television receives a video signal, it directs beams of electrons from the rear of the television tube towards its front. This vacuum sealed picture tube has many phosphor elements on its inside front face. When an electron beam hits a particular element, that element becomes excited and emits light. By varying the intensity of the electron beam and directing that beam to either a red, green, or blue phosphor element, a color picture is produced. By scanning the electron beam row by row across the face of the tube many times a second, a color moving image is formed.

How does a projection television work?
Projection televisions employ three separate tubes to produce the red, green, and blue elements of a color picture screen. The tubes themselves may be either in front of ( front projector) or behind ( rear projection) the actual screen. The tubes must be aligned or converged so that their output is focused and the full color spectrum can be produced. Liquid crystal display televisions, a newer technology now becoming more widely available, use a single tube as the RGB elements are converged internally.

What is a video signal?
A video signal contains the three elements which are necessary for the reproduction of an image by a television or monitor. The chrominanace, luminance, and synchronization signals are all part of the video signal. The chrominanace portion contains all the color information. The luminance portion controls the brightness and lighting of the image. The synchronization signal is necessary to control the scanning done by the television to make a moving image. If all of these are combined together, the resulting signal is called a composite video signal.

What is Super VHS?
Super VHS (SVHS) is a video signal in which the chrominanace and luminance signals are carried separately in order to reduce interference and lower overall distortion. Equipment with SVHS inputs and/or outputs, as well as SVHS cables, must be used to transfer this type of signal between components.

What is HDTV?
When will it be available? HDTV, or the High Definition Television standard, is designed as the next generation television broadcast signal. As agreed upon in the United States, HDTV will be broadcast as a digital video signal. It will contain many more lines of resolution as well as a 16:9 aspect ratio (the ratio of the television screen's width to its height). Unfortunately there is a great deal of controversy about its future broadcast. While originally slated for rollout during the 1996 Summer Olympics, various delays postponed its rollout. Special equipment will be needed to see an HDTV broadcast at home.

Why would I want a widescreen television?
Back in the 1950's, Hollywood came up with many tricks to get people out of their living rooms and into the theater. Perhaps the longest lasting of these features is the wide aspect ratio movie format. While regular television is broadcast at 4:3 (the ratio of the picture's width to height) movies have been shot in ratios even greater than 2:1. When such a movie is shown on television, if its full height is to be broadcast, its sides must be cropped to fit the TV screen, thus losing information originally intended for viewing. However, newer video formats, such as laser disc and satellite broadcast, often show a movie in its original format with blanking on the top and bottom of the picture to preserve its aspect ratio. Wide screen televisions allow the viewer to see the movie with little or no blanking, thus presenting the movie closer to its original format.

Home Theatre

Why would I want a widescreen television?
Back in the 1950's, Hollywood came up with many tricks to get people out of their living rooms and into the theater. Perhaps the longest lasting of these features is the wide aspect ratio movie format. While regular television is broadcast at 4:3 (the ratio of the picture's width to height) movies have been shot in ratios even greater than 2:1. When such a movie is shown on television, if its full height is to be broadcast, its sides must be cropped to fit the TV screen, thus losing information originally intended for viewing. However, newer video formats, such as laser disc and satellite broadcast, often show a movie in its original format with blanking on the top and bottom of the picture to preserve its aspect ratio. Wide screen televisions allow the viewer to see the movie with little or no blanking, thus presenting the movie closer to its original format.

What is THX?
THX is a set of technical specifications developed and trademarked by Lucasfilm, Ltd. for the playback of movies in theaters and homes. Designed to raise the level of soundtrack playback fidelity, THX now encompasses almost every aspect of the home theater. These specifications are minimum only and even manufacturers who license the THX standard often produce components with superior specifications. THX has succeeded in raising the public's awareness of the need for improved theater fidelity.

What is Dolby AC-3?
Dolby AC-3 is the next generation of surround sound encoding from Dolby Laboratories. While Dolby Pro Logic was an analog encoding scheme, AC-3 uses digital encoding to produce five discrete full range channels of surround information plus a bandwidth limited subwoofer channel. Although currently only available on laser disc format, Dolby AC-3 is the accepted sound format for HDTV and will likely be found on satellite broadcasts within the next year. Special hardware is required for AC-3 playback, although all sources will most likely be backward compatible with existing surround sound and home theater components.

Digital Audio

How does a compact disc work?
As with any digital encoding of an audio signal, a compact disc contains digital information (bits) which represent the frequency information of the signal in question. Each second of sound is looked at 44,1000 times a second and each discrete frequency is then represented by a sixteen bit digital signal. When this encoded information is read by a compact disc laser mechanism, it must then be reconverted to an analog waveform. This process is handled by a digital filter and a digital to analog converter, which separates the information into appropriately sized blocks allowing the converter to then recreate the analog signal. This signal then passes through some analog circuitry, which sends it along to the other components in the audio chain.

Why do some CD players sound better than others?
Despite some manufacturers' original claims, the compact disc was not perfect sound forever. Compact disc playback is an amalgam of many attributes, starting from the recording and mastering of the disc. Many factors inside a machine effect sound quality, beginning with the accuracy which the laser and transport assembly read the bits from the disc itself. The quality of the digital filter chips and the digital to analog converter, which work together to convert the digital signal to the analog domain have a great effect on a machine's sound quality. A poor conversion process can result in a thin, bright, and uninvolving sound. CD players also contain analog circuitry, which the signal passes through before leaving the player's outputs. Poorly designed analog circuitry in a player is equivalent to putting a mediocre preamplifier into a high-end audio system. All of these factors effect the sound quality of a CD playback system.

Amplifiers/ Preamps and Receivers

How much power do I need?

Amplifier power ratings, given in watts, often do not adequately reflect the amplifier's ability to deal with the reactance which a particular speaker may represent. An amplifier's output current is commonly more important than its power rating, particularly into impedance of less than 8 ohms. The impedance of a real world loudspeaker, which is the collective resistance it shows the amplifier, typically varies widely during music reproduction. Common playback levels and room parameters (i.e. size, damping, etc.) are other important considerations when considering an amplifier. The efficiency of the loudspeaker which will be used is also important. Always look at the loudspeaker's recommended power range (not its maximum power rating) and remember your environmental considerations when looking for an appropriate amplifier.

Why do some amplifiers sound different than others?
Design theory and cost considerations both have an effect on amplifier, preamplifier and receiver quality. Electrical design, including the power supply and circuit theory, play a large part in a component's sound quality. Better parts quality, from volume controls to capacitors, will generally improve sound quality as well. A component's interaction with the other system components can change its sonic signature too.

What's the difference between a class A and a class A/B amplifier?
Every audio signal has both a positive and negative (relative to ground) component. In class A operation, each output transistor handles both elements of the audio signal, thus working constantly. In A/B operation, two transistors are used, one for each half of the signal polarity. This design is more efficient, as each transistor is working only half as much as in class A. In actuality a class A/B amplifier acts in pure class A over a small percentage of its operating range and then switches to class B when greater output is needed. True class A amplifiers are quite rare because of their inefficient nature. They generate a great deal of heat, require a very large chassis, and consume much electricity. While pure class A amplifiers can produce a very sweet sound, high quality A/B designs can sometimes approach this without the tradeoffs of size, heat, and electrical costs. Low level circuits, such as preamplifiers almost always incorporate class A circuitry as it is easier to implement when dealing with smaller signals.

Why do some companies use vacuum tubes in their amplifiers?
The answer is simple - vacuum tubes amplifiers, when mated to an appropriate loudspeaker, can sound superb. While not known for tight, delineated bass control, vacuum tubes can offer a smooth, natural midrange and an unfatiguing, delicate treble. They can project a deep and wide soundstage. Their overall sound is often described as "liquid". So why doesn't everyone use vacuum tubes in their designs if they are so wonderful. First of all, the cost. A comparably powered solid state amplifier is less expensive to produce. Furthermore, tubes degrade in time much more rapidly than solid state devices, often needing to be replaced every one to two years. Second, not every loudspeaker works well with tubes. Certain speaker designs require greater current than tube amplifiers can produce in order to obtain good dynamics, transients, and bass control. Third, tubes are in general not as reliable as solid state devices. While any component can develop a problem, tube components have a reputation for lower overall reliability. Despite all of this, tubes can be found in a good number of components from high-end manufacturers. Some people will not listen to music without a tube somewhere in their system!

What's the difference between a receiver and an integrated amplifier?
A receiver is a combination of three distinct components put into a single chassis - a tuner, a preamplifier, and a power amplifier. An integrated amplifier combines only a preamplifier and a power amplifier into a single chassis. A tuner must be purchased separately if radio broadcast reception is desired.

What is the function of a preamplifier?
A preamplifier is the control center of your audio/video system. All of the source components of your system get routed through your preamplifier. Besides switching between components, your preamp also controls volume and balance. Most preamplifiers also apply a certain amount of amplification to the incoming signal before sending it on to the system's power amplifier. A line stage preamplifier is a preamp, which does not contain the appropriate circuitry for a turntable connection. In this case, adding a separate phono preamplifier is necessary.

Speakers

What is a satellite/subwoofer system?
A satellite/subwoofer system is a three or four piece loudspeaker system, which has been divided such that the satellites receive midrange and high frequency signals while the subwoofer receives only lower bass frequencies. The satellites tend to be smaller speakers containing a tweeter and a mid or mid/bass driver, while the subwoofer(s) is usually a much larger box containing at least one bass driver.

Will some speakers work best in certain rooms?
Room acoustics play a much larger part in overall sound quality than most people realize. Every room has its own frequency response characteristics. They all also have differing degrees of absorption and reflection. These factors will always impact the sound of your speakers. For instance, bright loudspeakers in an extremely reflective room may become excessively bright. Thinking about room contents (couches, rugs, etc.) and room design and construction (hardwood floors, large windows, etc.) can be extremely helpful when deciding on the correct loudspeaker. However, it is not a wise idea to choose a loudspeaker solely because you feel it will "match" your room. Room acoustics can be changed by moving furniture and fixtures, putting down rugs, or by adding acoustical room treatment.

Will some speakers work best in certain rooms?
Room acoustics play a much larger part in overall sound quality than most people realize. Every room has its own frequency response characteristics. They all also have differing degrees of absorption and reflection. These factors will always impact the sound of your speakers. For instance, bright loudspeakers in an extremely reflective room may become excessively bright. Thinking about room contents (couches, rugs, etc.) and room design and construction (hardwood floors, large windows, etc.) can be extremely helpful when deciding on the correct loudspeaker. However, it is not a wise idea to choose a loudspeaker solely because you feel it will "match" your room. Room acoustics can be changed by moving furniture and fixtures, putting down rugs, or by adding acoustical room treatment.

Where should my speakers be placed in my room?
Room acoustics and loudspeaker placement are part art and part science. Many books and computer programs have been written to explain and implement the study of room acoustics. There are several guidelines that can help you place a pair of loudspeakers. First, loudspeakers should always be placed on the same wall opposite the primary listening location. A triangle should be formed between the listener and the two speakers, with the listener slightly further from the two speakers than the speakers are from themselves. Speakers should generally have at least six (2 meters) and at most ten feet (3 meters) between them, depending on room size and seating arrangements. Speakers should be placed away from room boundaries by at least a foot, more if possible. Putting speakers too close to a rear wall will increase the bass output, sometimes making them seem boomy. Placement too close to a side wall will cause room reflections, which may degrade your stereo image. Placing speakers further out into a room may increase soundstage depth, but placement too far into the room may produce a thin low end. A final suggestion is to try angling your speakers in toward the listening position. This will effect the soundstaging and the tonality. Trial and error is essential to loudspeaker placement. Use these suggestions and see what sounds best in your environment.

Does a bass reflex speaker sound better than an acoustic suspension design?
The answer is no. For that matter, an acoustic suspension design is not "better" than a bass reflex speaker. Loudspeaker design and theory is a combination of many different theoretical and technical issues. The application of all of this theory still results in a loudspeaker which is not perfect. Subjectively, one can choose a particular speaker over another, but this is only a subjective choice. Successful and fine sounding bass reflex and acoustic suspension loudspeakers have been designed for many years. Specific choices can only be made after properly evaluating a particular product.

I want a small speaker but don't want to sacrifice bass response. What should I do?
One aspect of a loudspeaker which determines its lower frequency response is its internal volume. Larger speakers commonly have deeper bass than small speakers. While not all small speakers are created equal in this respect, a larger speaker will almost always outshine a smaller design in this aspect. So if you cannot live with a larger speaker, you can always add a subwoofer to supplement the low end response of your loudspeakers. While not necessarily small, a subwoofer is more compact than a loudspeaker tower. Proper room placement of a subwoofer to achieve good integration with your loudspeakers can be tricky however. Be prepared to try several locations for the best result. If a subwoofer is out of the question, try placing your speakers a bit closer to the rear wall. This will help to augment the speakers' bass output.

How tall should my speaker stands be?
The rule of thumb is that a loudspeakers' tweeters should by approximately ear level when the listener is sitting. This usually is somewhere between 36" (90 cm) and 40" (100 cm) from the floor. A speaker stand should be tall enough to place the tweeter at this level.

I want to put spikes under my speakers but I don't want to damage my floors. What are my options?
A simple trick to solve this problem is to put a small coin underneath each spike. The speaker will still be decoupled from the floor and the spikes will not be digging into its surface.