Copyright Michael Karbo, Denmark, Europe.
Chapter 13. The construction of a sound card
As I have mentioned earlier, sound cards are extremely complicated to understand and the best of them have an unbelievable number of functions.
Many of the functions are especially suitable for solving particular sorts of tasks, and it is very rarely that the same user needs to use all of them. Let me here name a handful of the very varied areas:
All these things can actually be done with a good sound card and appropriate software, loudspeaker system, etc. But, as you can probably guess, there are not very many, who need to use all of them. In the following section, I will try to describe the sound card’s different components, and what they are used for.
Fundamentally, a sound card consists of components like:
The first two devices have, in their own way, something to do with making sound. The third device (the DSP) is a little computer in itself. It manages coding and decoding in relation to 3d sounds, surround sound, etc., just like in DVD players, etc.
One the sound card’s most basic functions are to supply ”ready-made” sounds for, for example, games or MIDI melodies. This also means that the sound card ”contains” sounds, which a computer can make use of. Sounds like piano, bass, drums, guitar, organ, etc.
It is the sound card’s synthesizer, which supplies the sounds, and there are several systems. Sounds are created completely artificially with FM synthesis in the cheapest sound cards (Frequence Modulation). It is really the right synthesizer principle. The sounds are synthetic – it sounds a little like a piano, but it isn’t. FM synthesis is artificial sound and the result sounds like that. Wavetables and Soundfonts give the best sounds, but they are also a more expensive quality of sound.
The sounds are recordings from real instruments that are stored either on a sound card or on a hard disk. Recordings are made with a proper piano and a little sample is made in the light of the recording. ROM circuits (chips) are found in older sound cards, which have a permanent content of these samples (wave tables). The sounds are, so to speak, ”burnt” into the cards.
Figure 65.There are always ”ready-made sounds” (samples) that the sound card can play back. They are either on the sound card itself or as a file on the hard disk.
Today the better sound cards use SoundFont technology. The computer’s hard disk and RAM is made use of here for the sampled sounds. When the sound card’s software is installed, a collection of Soundfont files is copied onto the hard disk. From here they are read into the RAM and “linked” to the sound card.
Figure 66. SoundFonts is an advanced system for the programming of sound cards with high quality sampled sound. The sounds can be manipulated with programs like Vienna, which is shown here.
When you play back, for example, a MIDI melody, then it is the samples, that you listen to. This can give an extremely fine sound, where a piano really sounds like a genuine piano. All the better sound cards use both synthetic and sampled sounds, just like the electric pianos you can buy in music shops also do.
Playing a MIDI file on a computer can easily test a sound card’s fundamental quality. We shall be looking more closely at the concept MIDI, which works with music files without sound. When a MIDI file is played back, then it is the sound card’s own sound, which is played and it is, therefore, very easy to hear the difference between the various sound cards.
D/A conversion for playing back
The sound card is a link – a bridge, one could say – between the purely digital computer and the analog sound. This means, that you can direct analog, electrical sound signals into a computer and get them digitised. And the other way around the digital sounds can also be converted to analog sound signals in the sound card. Both conversions are made in the sound card in small DAC- and ADC chips (see earlier in the booklet, e.g. page 3).
Figure 67. The converter (DAC), which converts digital sound data to analog signals on Sound Blaster Audigy sound cards. The opposite conversion takes place on a corresponding ADC chip in the card.
D/A conversion is used when a sound card is used as a player. If it, for instance, is connected to a CD drive, then you can play a normal music CD. The digital soundtrack is directed from the CD drive via the motherboard to the sound card, where it is converted to analog signals.
The analog signals correspond to the ports from a headset port on a television or a radio. The signal can be sent directly to a set of headphones, which is very practical, in the case of sound from a computer. The signal can also be connected to a stereo amplifier or to a set of active loudspeakers.
A/D conversion for recording
A/D conversion is used correspondingly when you record sound on a computer. The sound signal is fetched from the sound card’s analog port. The signals are sampled and converted into data.
Every analog source of sound can be digitised with a sound card. That is to say, you can fetch sounds from a radio, a record player, a tape recorder, a video, a television, a microphone, electric instruments, etc. Anything, that has a headphone or a line port, can, in reality, be connected to the sound card’s analog port.
You have to be aware, however, of the fact that a record player’s signal is very weak. Which is why an additional amplifier has to be added (an RIAA amplifier, a little black box), which amplifies the signal up to the level expected by the sound card’s port. Read more about this in the IDG booklet ”Computer Audio”. The signal from TAPE OUT on a stereo loudspeaker or receiver can be directly connected to the sound card’s port LINE IN.
The result of the digitizing can be sound data, which is either ”raw” or uncompressed or sound files, which are packed into, for instance, the mp3 format. This is dependent on which program you use to make the recording.
Analog and digital plugs
So we have seen that the sound card’s A/D and D/A converters are used every time you either record or play back a sound with the help of analog devices. Of course, there has to be plugs on the sound card to enable the connection of these devices.
There ought to be two or three minijack plugs, functioning as analog ports (LINE IN and MIC) or (LINE OUT or SPEAKERS). Or else there will be digital plugs like the earlier mentioned optic port (TOSLink).
Figure 68. On the left you can see the optical, digital plug. The three other plugs are used for the analog devices. See also Figure 60 on page 3.
A sound card has a lot of other plugs than those mentioned here. In the next chapter, we will look at an example of a sound card and its options for connection.
Figure 69. Analog and digital ”ports” make connections to external sound devices .
The quality of a sound card’s D/A and A/D converters can vary a lot. With the cheapest sound cards, you can only convert PCM sounds, that are sampled with 44,1 kHz and a 16 bit resolution, while the better sound cards can manage much more powerful samples. All things considered, there really is a lot of difference in sound quality with regard to different D/A converters.
If musicians use a sound card for hard disk recordings, then it is important that the sound card has a powerful A/D converter, so that the sound can be recorded with the best possible quality. This is also necessary if the sound card is to be used for playing high quality Surround sound (e.g. DVD-Audio) via an active loudspeaker set.
Luckily, sound cards of good quality are not terribly expensive. Creative’s Sound Blaster Audigy cards are found in many designs with a starting price less than 1000 kr. The models differ in how many plugs and connections they have, and how much software they are accompanied with.
You can find extensive sound guides on the Internet (see the addresses on page 3), where the different cards are tested and compared. There, you can see that a card like Sound Blaster’s top model Audigy2 Platinum eX is close to being able to be compared with top professional cards like, for example, LynxTWO (Figure 70).
Figure 70. High end sound card used in music studios. Price: about $1000.