TO GO S/PDIF OR NOT
Written by Mathias C. Hjelt
V1.0 - 18 Sep 95
So, the AWE has got a digital output, we all know that. But what's the big use of it, really?
How much better does things get if it is taken into use? How much would that cost? Is it worth
the money and the effort? Questions like these are rather common, and I think they need to be answered,
so I gave it a try. That's what this page is all about.
General stuff..
Equipment, products, accessories..
The idea and the function of the AWE's S/PDIF - a short repetition
Anyone who has read all the pages should know exactly what the S/PDIF output is, where it comes from
and what it delivers, but here's a short summary anyway. S/PDIF is a standard for digital audio
transmission, and the AWE's digital output conforms to this standard. The output comes from the EMU-8000,
which means that all EMU and OPL3 synthesized music will come out this way, of course with the reverb,
chorus and QSound effects produced by the Effects Engine. The wave audio channel isn't connected to this
digital output. Further info can be found on these pages:
What can I connect to it?
A large number of devices has got a digital output that accepts S/PDIF. The device that probably interests
AWE users the most is a simple DAC, i.e. a box that turns the digital signal into an analog stereo signal.
The big idea behind this is that just about any external DAC with S/PDIF input will have a much cleaner sound
than the AWE's on-board stuff, better frequency response, and so on.
Many use the S/PDIF output to transfer their music digitally to DAT, MiniDisc or DCC. This is possible since most
digital recorders have S/PDIF-compatible inputs - electrical or optical. Professional effects processors, digital
multitrackers, all-digital pre-amps and that kind of devices can also be connected digitally to the AWE.
How much is the sound quality improved, and do I need it?
In theory, the sound quality of a digital output signal should be perfect, noiseless, have an unlimited and
unmodified frequnecy reponse, and so on. However, the AWE can't sound perfect even when digitally connected to a
perfect DAC, and some of you may think that the improvement is so small that it isn't worth the money it takes.
One thing is sure: the background hiss will disappear. With the term background hiss, I refer to noise that is
there even when no sound is playing. The AWE's on-board electronics have lots of background hiss - just turn up
the volume and you'll hear it. A decent external DAC will have less background hiss than a regular $200 CD player
- it's so low that you can consider it gone for good.
Unfortunately, the EMU hisses digitally. When a sample or a reverb trail fades, a little noise appears - the
"waves-on-the-beach" effect. Now that the background hiss is gone, this digital hiss becomes much more evident,
because as soon as all sound stops and the EMU only is transmitting zeroes, the DAC will become competely silent,
and this contrast between noise and total silence can be a bit annoying. However, this whole thing won't bother you very
much unless you have some really silent parts in your music and listen to it at a rather high volume - or if you
just happen to be as picky as I am, or if you're pro.
Now on to the frequency response. Even after disabling the Effects Engine's EQ as described on
the page about getting the best sound out of the AWE,
you won't get the perfectly straight frequency response you'd expect from a digital output. There is still going to
be a slight peak around 11kHz. Any regular DAC has got a much flatter response. However, this doesn't make the
whole thing unusable, but if it annoys you, you have to correct it with an external equalizer.
So, what's so great about this, besides that about the disappeared background hiss? Well, several things, and they
all aren't that easy to prove scientifically without advanced measuring equipment. Here are a few comments from
people around the net who have ran their AWE through external DACs:
- the sound is much clearer and "larger"
- the reverbs sound much better
- the bass has got more punch
- there's much less distortion and less hiss
These statements are of course not based on unbiased blind listening tests, but in any case they give some kind of
picture of what the difference between the on-board stuff and a real external DAC is like. The explanation to all these
improvements can't be found in a plain frequency response graph, the sound also depends on how big phase errors there
are (the phase of tones of different frequencies may differ slightly if the DAC is simple or if the analog signal runs
through too many and simple filters), interchannel delays / phase errors, linearity and monotonity errors, and stuff
like that.
Many MIDI musicians would probably be pleased with the improvements that an external DAC offers, but this doesn't mean
that everyone must go S/PDIF. I know that there are lots of AWE-musicians out there who actually are pretty
satisfied with the AWE's sound quality and don't feel bothered by the background hiss. They simply don't need external
DACs, and can just as well save the money and buying something more useful for it. And people who use the wave audio
channel a lot (for example with games and the like) would anyway have the hiss left on that stuff, and in case the wave
audio and the external DAC would be mixed together, no one could tell whether the synth stuff has got background hiss
or not. And so on, and so on. An external DAC is not always a necessity.
Personally I've found than an external synth DAC can be pretty handy in many cases. I was for example mixing wave audio
with synth music (I simply had to accept the noise), and found out that I needed to add reverb externally to the wave
audio, but not to the EMU stuff. This would be impossible if both signals came out through the AWE's line out. Being
able to equalize the wave audio separately from the synth stuff makes it possible to reduce the noise of the wave audio
channel. The possibility to transfer synth stuff digitally to a DAT is also cool if you're making demos and such stuff,
and this doesn't even require an external DAC, just a S/PDIF output connector and a cable.
So whether you personally need to go S/PDIF or not depends completely on your own demands, what you want to do, and if
you really think it's smart to put so much money on an expansion device for a sound card from 1993 or not. The best way to
find out would definitely be to get a chance to try out what it sounds like before purchasing a DAC. Perhaps you'll find
the improvement fantastic, perhaps you don't hear any difference at all and just get disappointed - it's so personal.
So, try first, buy then. And don't forget your own needs.
S/PDIF output connector
Since the AWE32 definitely was designed for the home game &
multmedia world, not for pro studios, Creative didn't want
to bother with the extra problems they would have faced if they had
wanted to provide a digital output connector on the
backplane of the card, and ended up putting in a tiny little
jumper-like connector as close to the source (the EMU) as
possible. As a result, you can't just "plug & play" - you first
have to install a cable & connector that brings the S/PDIF
signal from the AWE to a more accessible place (the back of the
computer) and uses a more commonly used connector type.
Many have decided to make this kind of a hack themselves, but since this definitely requires experience in
electronics and soldering, there sure is a demand for factory-produced connector kits. A few companies have reported
that they will start making these, but I don't know how many really have carried out this idea. The only company I've
seen marketing this kind of stuff is HWMS located in the UK - call 01694 731718 or
check out their Web page.
Many devices use optical links for digital transfers, but that's not a problem since the standard of the signal is the
same. If you want, you can make an optical output interface yourself, otherwise you could try to find a general
electric-to-optical converter.
Click here for a do-it-yourself description of electric & optical output connectors
S/PDIF cable
S/PDIF-compatible devices are generally interconnected using a cable with regular RCA plugs. However, according to the
standards and recommendations, a regular audio cable will not work (or should not be used) as a S/PDIF cable. The reason
for this is that a 44.1kHz audio signal turns into a 5.6MHz signal when it's bihphase encoded, and this is way beyond the
bandwidth of audio signals and the capabilities of cheap cables. So if you use a regular audio RCA cable for S/PDIF, you'll
face big, big problems. In theory.
Personally I've found that just about any cable will do fine. One of the cool things with digital signals is that the
data gets totally messed up if the connection is disturbed, and I haven't had any such problems with any type of cable,
ever. However, if you want to follow the recommendations and feel safe, get a 75 ohm RCA video cable from any video or
electronics store (yes, Radio Shack have them). Such coaxial cables are designed to cope with huge bandwidths and stuff
like that. The price depends on the store, but it's not going to kill you in any case.
All fans of Home Improvement will of course want to make their own cables, which is very possible. You can either make
a cheap one (simple, plastic RCA plugs & the cheapest cable you can find, price under $2) or a "reliable" and expensive
one (shielded, golden RCA plugs and real 75 ohm coaxial cable, price over $30). You decide. The standards don't recommend
lengths over 10 meters (33 feet), but that should be enough for anyone. Remember to make it long enough - a short cable
will only cause you trouble in the future. I hate short cables. When soldering the cable, make sure you connect the
shield of the cable to the shields of the RCA plugs - inverting a signal is never healthy. If you don't have a shielded
cable, the risk of connecting signal to ground and vice versa is of course bigger, but the standard doesn't say a word
about that. Be careful & ask your local Al for help if necessary.
If you're stuck with a piece of gear that only has got optical S/PDIF input, try asking for a suitable optical cable at
your local music store. I have no clue about how to make those yourself, but you could try and tell me how it turns out.
D/A converters
Now that you have a S/PDIF output interface in the back of your computer and a cable, you may want something to connect
this stuff to. There are several possibilities:
Dedicated D/A converters
There are all sorts of D/A boxes. Everything from cheap crap to super pro hifi gear that cost over 10 grand. For an
AWE user, the best choice is something that doesn't cost too much (if you pay a lot, you could just as well has purchased
another sound card from the beginning), and doesn't sound too bad (because the on-board one already handles that part
pretty well). These devices can be purchased from stores that carry music & studio gear.
Audio Alchemy manufactures a few D/A converters, of which the "DAC-in-the-box" obviously is the most popular one,
with a sound quality that could be regarded as pro, priced around $200. Their "DAC-MAN" is a somewhat lighter version
which costs quite a bit less. Always remember that quality - and good D/A converters - always cost. There's so no such
thing as cheap'n'good. But of course, sound quality is very subjective - what some people regard as pro, you may find way
too noisy for your needs, and vice versa. Let your ears be the judge. Always think about your own needs.
Digital hifi systems
There are a few all-digital hifi systems on the market. These futuristic kits do everything digitally, and some even have
the D/A converters located in the speakers. The preamps often accept S/PDIF-compatible audio sources, so an AWE can
successfully be used with this kind of gear. I don't believe that these kits are very common, but in case you have one,
you don't need to bother about purchasing a separate D/A for the AWE.
DAT - MD - DCC
Most DAT and DCC decks have digital inputs that accept S/PDIF information. Unfortunately it's pretty common that they only
feature optical inputs which makes interfacing with the AWE a bit more complicated, but those who have electric inputs
should work fine and can do D/A conversion for an AWE. MD machines obviously have these inputs too, and their D/As are
usually good although MD itself isn't as good as DAT or CD because of the compression method. So if you have a DAT, DCC
or MD around, try it out. It may save you lots of bucks.
Do-it-yourself
A few electronics magazines (Elector and those) have published schematics for professional-quality D/A boxes with S/DPIF
input. However, these usually have lots of extra, unnecessary stuff, and cost a lot to build. I'm currently in the process
of designing a cheap but pro D/A box of my own, but since this is far from easy and I have little time to spend on this
kind of stuff, all I have at the moment is a prototype which doesn't work perfectly. A new one is under process. To read
more about this project, click here.
In general, it's not a good idea to make audio gear of your own. Although this kind of stuff is very simple in theory, it's
very difficult to make it work out in reality. Noise, hum, EMI (electromagnetic interference), radio reception, etc - that's
the kind of problems you'll run into. To save time and sweat, go for an off-the-shelf D/A instead of making your own.