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Setting up Home Theater

This page is a record of my experiences trying to get surround sound to work with a dual-processor 1 GHz Powermac. Unfortunately documentation for these issues is a bit hard to find. Some of the material is specific to the Mac, but I've tried to be helpful for people with PCs also.

The main difference between Mac and PC are

Do you really want to do this?

This page documents a setup where the actual playback is done on a Mac. DVDs are played using DVD Player.app, and music using iTunes.

Another option is to do everything externally, using a separate DVD/CD player. There are advantages to that. It puts you in the mainstream, where it's easy to get hardware that supports all the most recent formats. The Mac is not as well supported as the PC for home entertainment, so if you use a Mac you're going to have to spend more time identifying hardware and software that works with it, and you may not have access to certain newer multimedia formats (e.g. some of the high-definition video and audio formats).

At this point I'm using the Mac for two reasons:

How it works

The big problem in doing movies on the Mac is the sound, not the video. DVD Player produces acceptable video. I use it. However some people think it's not quite as crisp as the best PC software. I've seen suggestions to use VLC, at www.videolan.org. I have two cautions about VLC: (1) It should be used only by people who are forgiving of software that is less than production quality; (2) it uses licensed technology without paying the license fees.

The main reason surround sound is a problem is because DVDs and other media store their audio in an encoded form. This is done to save space on the CD or DVD. Having 6 tracks at full bandwidth would take up too much of the DVD: there wouldn't be much left for the video. So the sound is compressed using special techniques that make use of what we hear and what we can't. There are three common formats:

[In this document, I discuss 6 channel output. There are newer "EX" versions of Dolby Digital and DTS that carry 8 channels. They include two additional channels for the back. This is called 7.1. There is also a 6.1 format, with one back channel. The issues in supporting 6.1 and 7.1 are the same as 5.1. They just require more channels. Generally your receiver can convert between formats, to fit the number of speakers you have.]

The big question is handling surround sound is where these formats are decoded. There are two main options:

Normally software decoding is used with inexpensive "multimedia" speaker systems sold primarily for use with computers. These systems are "active", meaning they contain their own amplifiers. The computer is expected to have a sound card that outputs the 6 channels through 6 separate analog connections. These connections are "line level", meaning that they haven't gone through the final amplification needed to drive speakers. (The 6 connections normally are carried through 3 cables. These cables use stereo connectors, carrying 2 channels in each cable.)

Normally external decoding is used with standard "hifi" equipment. The decoding is normally done in a receiver, which also has the amplifiers necessary to drive the speakers. The encoded audio signal is sent as a single stream, using a technology called S/PDIF. S/PDIF can be sent over either an optical fiber or coax. So the DVD player takes the sound off the DVD in encoded form, and sends it as a single signal to the receiver over the S/PDIF connection. The receiver decodes the Dolby or DTS format, producing the 6 separate outputs, which then go to speakers connected to the receiver.

The computer has a "sound card," which has the connections for the multimedia speakers or receiver. The more advanced sound cards can support either style of operation. Thus they have 6 or more line level outputs for use with software decoding, and 1 S/PDIF output for use with external decoding.

While the discussion so far has concentrated on DVD output, you may end up using games or other software that generates multi-channel output directly. In many cases this will not be Dolby or DTS encoded. Thus even if you are using an external unit such as a receiver, you may need the ability to send multiple channels to it, in addition to the encoded Dolby/DTS signal used for DVDs. S/PDIF has the ability to send multiple audio channels multiplexed over one cable. This output mode is called "PCM". Alternatively, you can connect multiple line level outputs from your sound card to your receiver.

When you look at a sound card, make sure you understand whether it supports multi-channel PCM or multiple line level outputs. Some of the M-Audio cards support Dolby/DTS encoded data, but other than that only have 2 channel output. These cards will work fine for DVD playback using external decoding, but would not work well for games or other software that generates multiple channels.

With a PC, it is fairly easy to use either software decoding or external decoding. The Macintosh has some limitations:

A few sound cards support S/PDIF, but can't send encoded digital over it. These cards don't seem very useful. Thus when you buy a sound card, make sure that you verify that they can send encoded Dolby/DTS output. (This is often referred to as Dolby/DTS "passthrough" mode, because it passes through the encoded data to the external device without any processing.)

Sound cards

As indicated above, you need a sound card that has 6 or more line outputs (for software decoding) and/or an S/PDIF output that supports Dolby/DTS passthrough (for external decoding).

PowerMac G5's have an S/PDIF output builtin, that does support passthrough.

For the PC, there are many sound cards available, many of which have both multichannel line outputs and S/PDIF output. If you are planning to use software decoding on the PC, make sure you have DVD player software that can decode Dolby Digital and DTS. Many sound cards come with Dolby/DTS-enabled versions of WinDVD or other DVD players. When you buy a sound card, check to see whether it comes with software that will meet your needs.

For the Mac, the only cards I know of that support S/PDIF with passthrough mode are made by M-Audio. Other vendors make sound cards that produce S/PDIF, but the ones I've seen don't support more than 2 channels over the S/PDIF.

I'm not going to review cards for the PC. They are changing all the time, and it's not hard to find reviews in the PC magazines. So this section is a brief discussion of some of the M-Audio cards for use with the Mac.

Unfortunately the Mac cards all have oddities with their device driver software. Make sure when you buy a card you have the right to return it if it doesn't work.

Here are the cards I know about for the Mac:

M-Audio makes more cards, but I don't have information on the stability of their drivers.

My current recommendation for the Mac is Revolution 7.1 if you can use a PCI card, and Sonica USB if you need USB and can get it. If you can't get it, it's worth trying Transit USB.

Receiver

If you're using a computer "multimedia" speaker, you don't necessarily need a receiver. Those speaker systems are designed to plug in directly to the line level outputs of the sound card. Of course this works only if you are using software decoding. That means you must have DVD Player software that can do Dolby/DTS decoding.

If you're going to do external decoding, you need an appropriate external device. Normally this means an AV Receiver. An AV receiver combines Dolby/DTS decoding, an AM/FM radio, and amplifiers to drive speakers. The receiver will need to have an S/PDIF input, which you will connect to the S/PDIF output of your sound card.

Receivers are normally designed to drive typical hi-fi speakers. These need amplifiers. If you are using a computer multimedia speaker system (or any other system with its own amplifiers, e.g. active monitor speakers), and you want to use external decoding, you will need to get a receiver that has line outputs for every channel. Some low-end receivers have outputs for normal speakers, but not the line outputs needed by a computer speaker system.

Why would you buy a receiver to drive computer multimedia speakers, since those are designed to connect directly to the sound card? On a PC you probably wouldn't. However on the Mac, there are no commercial DVD players that do software decoding. If you are uncomfortable relying on VLC, you might prefer to do external decoding. In that case the usual approach is to get a receiver and connect it to the computer using S/PDIF.

As indicated above, you will use an S/PDIF cable to connect your sound card to your receiver. S/PDIF can be sent over either optical or coax. Make sure your sound card and receiver support the same format. Many receivers will handle either optical or coax. There are two different types of optical connector, TOSLink and 1/8 inch. TOSLink is the more recent, and is probably preferred. However many older devices have 1/8 inch. There are even devices that use the same jack for a normal 1/8 stereo cable or an optical connection. Such a jack has a interesting combination of laser and metal connections. You may well find yourself with a receiver that wants TOSLink and a sound card that outputs 1/8 inch. Radio Shack makes a clever optical cable where both ends can be switched between TOSLink and 1/8 inch. There are also converters available.

S/PDIF over coax uses the same kind of cable you'd use for video: 75 ohm coax. The cable looks the same as a common type of audio cable. However I'd suggest using cable intended for either video or S/PDIF use.

I know of no reason to prefer either optical or coax: they both do the same thing. There is no good reason to use expensive cable, either optical or coax. Radio Shack should be fine.

Software

You'll need to install the driver software that comes with your card. (Go to www.m-audio.com or other vendor site and get the most recent version.) On the Mac, you'll end up doing settings in several different places. There should be equivalents on the PC.

Setting up your subwoofer

Most surround sound systems use 4 to 6 small to medium size speakers and one subwoofer. Full-range speakers are both too large and too expensive for most people to get 4 or 6 of them. So you get 4 to 6 speakers that can handle frequencies down to about 100 Hz, and one subwoofer that handles frequencies below that. The frequency where the main speakers stop and the subwoofer takes over is called the "crossover frequency."

If you have a receiver, it will act as a crossover. It will send frequencies above the crossover frequency to the main speakers and frequencies below it to the subwoofer. Thus you need to tell the receiver what to use as the crossover frequency. For computer multimedia speakers, the crossover frequency is normally fixed.

There are two other possible configurations. One is to use full-range speakers all around. In that case you don't need a subwoofer, and so you don't need a crossover. However even if all of your speakers are full-range you may still prefer to use a subwoofer, just for the "LFE" channel (low-frequency effects, the .1 in 5.1). Putting occasional loud explosions through your main speakers may require a much more powerful (and more expensive) receiver. The subwoofer normally has its own amplifier. If you're just using the subwoofer for the LFE, you would tell the receiver that your speakers are all "large" (i.e. full-range), but you have a subwoofer. In that case the receiver should just send the LFE signal to the subwoofer. You shouldn't need crossover in that case.

The other possible configuration is full-range speakers in the front, and smaller speakers for surround. If you tell your receiver that your front speakers are "large" and the others small, it will route all the low bass to the front speakers. You will still need to set a crossover frequency, which tells the receiver how low a signal it can send to the "small" speakers. As a variant, you can use large front speakers, small surrounds, and a subwoofer just to handle the LFE.

The range below 80 is really important for movies: it's where all the explosions and other sound effects are. For music it's less important: only a few organ pedal notes and a couple of other things get that low.

There are a number of issues in setting up a subwoofer:

The goal is to make the transition between the main speakers and the subwoofer smooth. Thus the levels needs to be matched carefully. If the subwoofer is either louder or softer than the other speakers, the system will sound unbalanced. With computer speakers, normally the only adjustment is the level of the subwoofer. With a receiver and hifi speakers, the crossover is done in the receiver, which normally lets you set both the crossover frequency and the level of the subwoofer.

For the Mac, I recommend downloading Audio Toolbox OSX, from http://www.blackcatsystems.com/software/audiotoolbox.html. Set it up to generate test tones from 200 down to as low as your subwoofer will go. (You can also get it to do a smooth sweep across the whole range.) Adjust the subwoofer volume until the volume is as consistent as possible across the whole range of frequencies.

If you can adjust the crossover frequency, I recommend checking out your main speakers by disabling the subwoofer and seeing how low the main speakers go. Similarly, check how high your subwoofer goes. Experts recommend that you choose a crossover frequency 1.5 to 2 times the lowest frequency your main speakers can reproduce before they start falling off. However you may not be able to do that with inexpensive speakers. Larger speakers will typically go down to 50 Hz or so, giving you 80 to 100 as crossover. That's fine. But smaller high-quality mains (such as the JBL N24II's that I use) fall off below 75. The standard rule could lead you to 150 as a crossover frequency. I'm nervous about going much above 100, for two reasons: (1) it may be pushing an inexpensive subwoofer (2) with frequencies above 100, you start being able to hear the direction from which it's coming. Thus a single subwoofer no longer works.

To do this analysis in a really scientific way you would want to get a sound meter. Radio Shack sells them for about $50. However I found that I was able to do OK without the meter.

The big problem with bass response is that you may get huge peaks. When I installed a well-known 2.1 multimedia system, I found that any DVDs that had low frequencies were painful. One particular frequency range (around 55 Hz) was booming so loud that it hurt. But if I turned down the subwoofer's volume so this wasn't a problem, I was missing a lot of bass.

There are two reasons for this:

Note on speakers

There is a big difference between computer multimedia speaker systems and even inexpensive hifi systems. If you can afford several hundred dollars, I strongly recommend getting a receiver and speakers, rather than a computer multimedia speaker system. I would start with 4 speakers and possibly a subwoofer. In theory you need 5 speakers and a subwoofer. However as long the front left and right are good speakers (have good "imaging"), and they aren't too far apart, you may be able to do without a center speaker. The receiver will automatically reroute the center channel to the left and right front speakers.

If you shop carefully you should be able to find a decent receiver for $200 or so (look for sales and discontinued models). The most commonly recommended low-end speakers on the AVS forums cost $190/pair. However there are a number of good brands of speaker, several of which have products at this price point. You can probably find one of them on sale. (E.g. I got speakers that at least match those at $79/pair, because they were being discontinued.) A decent subwoofer is probably going to be at least $200, and at that price it won't go as low as more expensive units. You may have to decide whether you care more about loud explosions or good sound. If you're willing to compromise on explosions, consider starting without a subwoofer and adding one later. (I'm using the subwoofer from an old computer multimedia speaker set. The other speakers in the set are junk, but the sub is pretty good.)

I recommend spending some time in the receiver and speaker sections of www.avsforum.com before buying anything. They can alert you to what's good and what isn't, which may enable you to locate bargains on E-Bay and elsewhere. While you can find worthwhile bargains, there's also a lot of junk out there.

You'll want to listen to speakers before buying them, because personal preferences are really important with speakers. More than any other component, different people react very differently to the same speakers. However there are problems with listening. Most stores have lousy setups for serious listening. They are noisy, play music you can't judge, and the setups themselves are often faulty. The right way to shop for speakers is to bring a CD with you that you know well, and to compare it in a quiet environment. Be aware that in quick comparisons, louder speakers will sound better, so you have to match volumes carefully. Some dealers with push specific speakers by setting them slightly louder. Since good comparisons are normally impossible except in high-end audio stores, most people narrow the field to a few candidates and insist on trying them at home. At the very least, make sure you can return the speakers if you aren't happy with them at home.

It's important to understand that there are things that make speakers sound impressive in a quick test, but won't do well in the long run. A good speaker is neutral: it plays music exactly as it was recorded. However in a quick listen, many people will choose speakers that emphasize the bass or treble. Speakers that don't have low bass will sometimes cheat by emphasizing the mid bass, thus giving the impression of having a lot of bass even though the low frequencies are missing. Similar emphasis at the high end is also common. It's hard to recognize these tricks without experience. But there are a couple of approaches. One is to compare with a well-rated expensive speaker system. Another is to go to a concert (or even a church service) immediately before listening to speakers. [It is important to choose your reference high-end speakers carefully. There are some expensive systems that are notoriously inaccurate. Unfortunately these include one best-selling brand. The speaker section of the AVS Forums can help you here.]

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Last updated: Tuesday, 13-Jul-2004 00:19:14 EDT
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