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
- There are more multichannel surround cards for the PC. For the Mac you pretty much have to use an M-Audio product. For the PC there are many good candidates.
- Device drivers for the PC are likely to work better.
- There are commercial DVD players for the PC that do software Dolby/DTS decoding. In the discussion below I indicate that for OS X if you want to decode in software, you have to use VLC. For the PC, there are editions of WinDVD and others that will do Dolby/DTS decoding. When you buy a sound card, you should expect it to come with a Dolby/DTS-enabled version of WinDVD or some other product.
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:
- My primary monitor is a 20" Cinema display. There's no obvious way to attach this to an external DVD player. There are a few DVD players that support DVI output. However the content owners have forced the DVD players to talk to displays using a special encrypted format. The Apple cinema display doesn't support this. If I were doing it again, I'd consider looking for a monitor that is designed to act both as an HDTV display and a computer monitor. There are some.
- I sometimes want to take screenshots, to put in notes.
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:
- Matrix multichannel. In this format, there are two normal stereo tracks. Surround sound is added by using out of phase signals and other tricks. The most common matrixed format is Dolby Surround.
- Dolby Digital. This is a discrete multichannel format, that normally carries 6 channels: front left and right, back left and right, front center and special effects. This format is called 5.1, with the .1 referring to the special effects channel.
- DTS. This is another discrete multichannel format, with the same 6 channels as Dolby Digital. It produces similar results to Dolby Digital, although the actual format is quite different.
[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:
- Decode in software: In this technique, the DVD Player software decodes the multichannel formats. It outputs 6 or more separate channels of sound, which are intended to go to the corresponding speakers.
- Decode in external hardware: In this technique, the DVD Player software sends the soundtrack in its encoded format to an external unit (normally an AV receiver). That unit decodes the sound and sends it to the speakers.
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:
- There is no commercial DVD player that can do software decoding. The only commercial DVD player is Apple's DVD Player.app. All it can do is output normal stereo, or the encoded Dolby/DTS for use by an external decoder/receiver. There is a free application, called VLC, which can do software decoding. However it is not trouble-free. When version 0.7.3 of VLC is released, it should support both software decoding of Dolby/DTS and passing the audio data to an external decoder. However my tests so far have not been entirely successful.
- If you have a G5, it has a builtin sound system that can handle multiple channels. However the only multichannel output it has is S/PDIF. (Of course it has a normal stereo output.) This means that it will only support external decoding. Of course you can always add a separate sound card if you need separate line outputs, e.g. if you have a computer multimedia sound system. However it may be a better investment to buy a receiver, and do external decoding.
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.)
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:
- Revolution 7.1. This is M-Audio's consumer PCI card. It's the one I am currently using. It caused system crashes when it was first released, but the current drivers appear to be stable. It has coax S/PDIF output and 8 line level analog outputs. S/PDIF works for 2-channel output and Dolby/DTS passthrough. It does not support more than 2 channels over the S/PDIF connection, though you could connect the 8 analog outputs to your receiver to handle multichannel output. Apple's DVD Player and VLC 0.7.3 beta work when using passthrough over the S/PDIF output. Multichannel output mostly works using VLC, but I got only one of the two surround channels. Perhaps this will be fixed in the final release of 0.7.3.
- Sonica USB. It talks to your computer by USB, and outputs over S/PDIF optical. It has been reported to work reliably, and to support stereo and Dolby/DTS passthrough. From the documentation it appears that it may not support multi-channel PCM output. I.e. for applications other than DVD playing, it may only support 2-channel output. It's not clear whether this unit is still being made, though at the moment people still seem to be able to buy it. Note that there is another product, Sonica Theater. That's a completely separate product, which I don't know enough to comment on.
- Transit USB. This is similar to Sonica USB, and probably should be its replacement. Many people had system crashes with it, but most people found that OS X 10.3.4 together with the most recent drivers fixed it. Even with current software, I got crashes, but enough people report success that it's worth trying.
- Audiophile 2496 PCI Card. This is similar to Revolution 7.1, but supports only 4 channels. The software is stable, but in my tests it didn't do quite what I wanted. I was unable to get Dolby/DTS passthrough to work, and when I tried to use 4-channel output with VLC, it put the center channel out my right front speaker. It's possible that these problems could be resolved. Unlike the Revolution, this supports 4-channel PCM output. Thus if you are using external decoding, the S/PDIF connection is all you need.
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.
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.
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.
- System Preferences, sound: Sets output for all software except DVD Player and VLC. I recommend routing this over the S/PDIF output. To do this pick "Digital Output".
- The card's own control panel. If you use S/PDIF output, you probably won't need to do anything here, though this depends upon the card.
- In applications/utilities, Audio MIDI setup. That lets you set the default output (the same thing set by System Preferences, sound), and also look at the format being sent over S/PDIF. This can be useful as a debugging aid. The OS should switch modes automatically, so you shouldn't need to change anything here. However once I found it trying to play a CD using 48 KHz rather than 44.1 KHz. This results in bad sound. It was easy to change. (In fact this morning I found that it had inexplicably changed the format to 8 KHz. Not surprisingly, I was hearing a definite lack of treble!) I've also had to change manually between 2 channel and encoded (Dolby/DTS passthrough) a couple of times. If you're getting no output, look here and make sure that the output format is consistent with what your application is producing.
- In DVD Player, Preferences, Disc Setup, Audio, Audio Output, you will want to choose "Digital Output." If you don't do this, DVD Player will use the normal system output. While it will end up going through the S/PDIF output, it will get converted to normal stereo rather than a multichannel format. When you put DVD Player into Digital Output, it will use Dolby/DTS passthrough (i.e. it will put the audio into the mode that Audio MIDI Setup calls "Encoded Digital.") Your receiver should then recognize it as either Dolby Digital or DTS, and light an appropriate light.
- In VLC, Audio, device, you have three reasonable choices: Stereo PCM (2-channel digital output), multi-channel PCM or analog (causes VLC to do the Dolby/DTS decoding), and Digital A/52 (Dolby/DTS passthrough, causes your receiver to do the Dolby/DTS decoding).
- When playing a DVD, you may need to choose the output track. Every DVD is required to support 2-channel output, which is almost always Dolby Surround encoded (if the movie was filmed with multi-channel sound). Most recent DVDs also support 5.1 Dolby Digital. A few DVDs also support 5.1 DTS, and/or the 7.1 "EX" formats. Typically the default is either 2 channel or 5.1 Dolby Digital. If the default is 2-channel, you will need to go into the DVD setup menu to switch to Dolby Digital. (You can also do this with the audio track option within DVD Player or VLC.) Most receivers will show you whether they are seeing Dolby Surround or Dolby Digital. If you don't see Dolby Digital, go into the menu and choose the right audio track. There are differing opinions about the advantages of Dolby Digital vs. DTS. Tests suggest that as normally used the technologies should produce about equivalent results. However in certain DVDs one or the other track may sound better. So it's worth trying both. Be aware that the DTS track is often louder. When comparing sound, most people hear the louder one as better, so you'll need to be careful to match volumes when comparing. Otherwise you may conclude that the DTS track sounds better simply because it's louder.
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:
- Where to put it
- Choosing a crossover frequency
- Adjusting the volume of the woofer
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:
- Rooms have "resonant modes". These are particular frequencies where the room resonates. There are various ways to minimize this, including changing the position of the speaker (away from walls, and particularly corners, but in general just try different positions) and buying special damping material. Better receivers let you set filters that lower the volume at specified frequencies. NOTE: You need notch filters or 1/3-octave graphic equalizers for this; the typical graphic equalizers have bands that are too wide.
- Some subwoofers, particularly inexpensive ones, have frequency response curves that look like a mountain peak: they have a large peak at one particular frequency. There's no answer I can think of other than not to use those products. In general you're probably better off without a subwoofer than with one that has really bad peak like that. Of course it's hard to know: vendors won't tell you about it, and you may not be able to tell whether a peak is due to the speaker or a room resonance. About all I can say is to make sure that you can return a speaker system if you can't make it work in your room. (I suspect that in my case the problem was actually the speaker.)
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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