computer audio, schede audio, software audio, soundcard, soundcard programming
computer audio, schede audio, software audio, soundcard,
soundcard programming
Nearly every PC nowadays comes with a sound card. They vary immensely in sound quality, features and input/output options. Sound cards fall into two distinct groups - consumer and professional.
The card that comes with the computer would slip into the consumer group, which means usually the cheapest card that the computer manufacturer can find the laters buzzwords like "3D audio", and is put there to make noises for computer games.
Professional (or prosumer - an in between category) cards often have multiple higher quality inputs and outputs, a much higher price and are usually bought later as an add-on. Pro cards usually have LINE inputs only, leaving the Mic pre-amp option open for users to choose. Professional audio equipment runs at a nominal level of +4dB, consumer at -10dB. Sound cards that are designed to link to other pro equipment will run at +4dB, and have greater headroom.
Practically all normal PC soundcards have a built-in computer controllable mixer functionality which is used to adjust how loudly different sound sources sound out and also controls what is being recorded by the soundcard. IN Win95,98,NT etc then there is a little speaker icon in the bottom right hand corner of the screen and double-clicking it will start you the mixer application which allows adjusting those soundcard settings. In other operating systems this adjustment is usually a separate piece of software which you need to run to do those things. If you do not have any idea what would be good settings for those differen sliders, it is a good idea to set about 1/2 to 2/3s up for each fader, and then adjust from those settings to direction which works best for you.
The Musical Instrument Digital Interface (MIDI) enables people to use multimedia computers and electronic musical instruments together. There are actually three components to MIDI, which are the communications Protocol (language), the Connector (hardware interface) and a distribution format called Standard MIDI Files.
The MIDI protocol is an entire music description language in binary form. Each word describing an action of musical performance is assigned a specific binary code. MIDI codes are like CPU machine language instructions for musical instruments. First a byte gives the instruction, if there is parameters, they follow the instruction byte using data bytes. Most typical MIDI control commands are:
MIDI was designed for keyboards, so many of the actions are percussion oriented. To sound a note in MIDI language you send a "Note On" message, and then assign that note a "velocity", which determines how loud it plays. Other MIDI messages include selecting which instrument to play, mixing and panning sounds, and controlling various aspects of electronic musical instruments.
According to the MIDI 1.0 Specification, the only approved MIDI connector is a 5-pin DIN connector. It is certainly possible to send MIDI messages using other connectors and cables, but it can cause interconnection problems. A major design goal of MIDI is to prevent any ground loops that might occur with the MIDI cables. This is done by using a balanced current loop through an opto-isolator and only grounding the MIDI outputs. The MIDI IN connector is not grounded to the receiver's chassis. When done correctly, there are no ground loops and no hum or other noises caused by the MIDI setup. A PC soundcard exports the serial MIDI signal from its UART on two pins of its joystick or game port. A special cable with electronics in it converts this to the approved MIDI connector, and is supposed to include the necessary opto-isolator for conversion to the required balanced current loop (some PC MIDI cables do not do the isolation and grounfing correctly!).
When MIDI messages are stored on disks, they are commonly saved in the Standard MIDI file format. The Standard MIDI File (SMF) is a file format used to store MIDI data (plus some other kinds of data typically needed by a sequencer). The purpose of MIDI Files is to provide a way of interchanging time-stamped MIDI data between different programs on the same or different computers. The format was designed to be generic so that the most important data can be read by all sequencers. The SMF format stores the standard MIDI messages (ie, status bytes with appropriate data bytes) plus a time-stamp for each message (ie, a series of bytes that represent how many clock pulses to wait before "playing" the event). The format also allows saving information about tempo, time and key signatures, the names of tracks and patterns, and other information typically needed by a sequencer. One SMF can store information for numerous patterns and tracks so that any sequencer can preserve these structures when loading the file. A track usually is analogous to one musical part, such as one instrument. A pattern would be analogous to all of the musical parts (instruments) for one song.
Most commonly used digital audio file format in computer is .WAV file. The .wav file structure is Microsoft/IBM RIFF file format of type WAVE with a fmt and a data chunk. The wav file format supports a wide variety of audio data formats, including mone, stereo, 8-bit (offset binary), 16-bit (two's complement) and higher, linear PCM, ADPCM, u-law, A-law, MPEG, AC-3 and so forth. The most typical .VAW files you might see are 16-bit linear PCM files.
PC99 standard defines the following color codes to be used for PC soundcard connections:
Line level outputs on consumer PC soundcards can typically output signals up to 2V levels and ouput impedance typically from tens of ohms to few hundred ohms (quite typical is 30-400 ohms). Those line level outputs are designed to be connected to consumer equipments (normal Hifi amplifier with -10dB nominal level line input) or powered multimedia speakers. Just get the suitable cable in between the computer and the Hifi system and you have your sound on on main speakers. The normal line level output of this kind can normally nicely drive up to around 5-10 meters of cable without any noticable effect to sound quality.
The typical 3.5 mm output jack used usually for all soundcard connectiond has the following pinout on signal output:
In some soundcards the line output is provided using pair of RCA jacks which are typically used for interconnecting consumer audio devices. In any case all you need is a suitable cable (cable with RCA conneector on one end one which fits to your soundcard) to hook your PC to your HIFI system line level input (for example CD, AUX or TAPE audio input). You can use the following input jacks: AUX audio, CD audio, CD-V audio, in order to connect the Line Output of the sound card to the Line input on the AUX function. Those inputs you should primarily try to use for PC soundcard. If you do not have those you can try tape inputs. Note that phono inout is meant only for connecting a record player to in and is not suitable for computer soundcard hookup.
If you happen to for some reason get some annoying humming (this happens in some case bit not always) then take a look at Ground loop pages to get information how to solve this problem if you get it.
Some soundcards have headphone outputs instead of line output. The specification of headphone output could be for example 100 mW to 8 ohms. This kind of headphone output can be used to drive hadphones directly. You can used headphone output like a line output to connect you soundcard to you HIFI system. If you don't have a line out, a headphone out will drive a line in of HIFI system very nicely. Just turn its volume down some to get the level into the right range. Quality will usually not be quite as good as a line out would be, but it will be at least good enough to serve for the crappy sound chip that's in your laptop (Practically every laptop has a crappy built-in soundcard). The usual offense is poor SNR due to large amounts of background noise picked up from the hard drive, various buses, etc.)
Speaker level outputs on some soundcards (not in many newr ones) have typically around 2W of output power and can drive 8 ohm sepakers or 32 ohm headphones nicely. If you have non-powered speakers or headphones, this is the output to use for them.
Typical line level audio input connections are generally designed to accept audio signals in the range of 500 mV to 2V. They are designed to operate nicely with consumer equipments like tape decs and CD players nicely (those devices use typically -10dB signal level). You can easily connect the tape output connectors form your HIFI amplifier into your souncard inputs and so get you HIFI system connected to souncard input (now you can use amplifier source selectors and record to any signal source in amplifier or connected to it). Line level audio input connectors are high impedance inputs (typically around 10-47 kohm). The pinout is the same as in the line level output:
The real performance and voltage rages of line inputs vary from card to card. Most cheap consumer sound cards run off a 5 volt internal supply so any buffering opamp stages they have will clip someplace around 1.5-2 volts. Some better cards can easily produce unclipped 2 volts rms. Some cards designed for professional use can handle input levels up to 10V.
When using the audio input connected take a note that there is a difference between which inputs are made available to the soundcard's output, and which one is made available for recording. To be able to record the sound from the input you must select that input for recording use before you can record anything from it.
Most sound card inputs require a minimum signal level of at least 10 millivolts. Sound Blasters and some older 8-bit cards need 100 millivolts. Many soundcard supply bias voltage on their outputs to power the electret microphones (the only microphone type which works with this kind of cards). The input impedance of the typical PC soundcard microphone input is typically in order of 1500 to 20000 ohms (can vary from card to card).
This discrepancy means that if a typical professional microphone is connected to a sound card input, the user will have to shout into the microphone or hold it just an inch or so away (or both) in order to produce a strong enough signal for the sound card to "hear." Other problem with dynamic professional microphones is that dynamic microphones do not like DC current, but soundcards have 1-5V power supply for feeding Electret mics on the 3,15mm-jack´s ring, which can touch the tip of the connector when you plug your microphone in and if you are unlycky it cna damage your microphone.
There are two possible solutions for the low volume problem with professional microphones connected to soundcard. First option is to try to increase the sensitivity of the sound card input with the control software which come with the soundcard (audio mixer application or such). This might more or less help depending on soundcard used. If the input sensitivity cannot be increased eough, another option is to amplify the microphone signal before it goes into the sound card input. This can be done by running the microphone signal through a device called a mic preamplifier or mic-to-line amplifier and feed that signal to the line level input in the soundcard (this approach usually gives better sound quality also).
Note for serious audio recorders: Soundcards with mic inputs on minijacks are usually low-quality devices, which means that htey are not suitable for high quality recording odf audio (they are still OK for general multimedia use or internet telephony). Such sound cards are not designed for high quality recording. Get a real soundcard and use a real audio application if you want quality results. If you want to get good quality microphone recording using computer the microphone wiring should be balanced and the microphone preamplifier should be external to the computer casing.
Generally the most troublesome task for people trying to record using soundcard is getting the sounrcard settings right so that they can start recording from the correct source with their favourite sound application like Cooledit, Goldwave or the basic Soundrecorder with Windows. To get the recording settings right in Windows system you just need to go into the Windows Volume Control (double-click on the speaker icon in your system tray) and make a few adjustments:
First go to Options, Properties, be sure you are looking at Playback, and check all the checkboxes so you see all controls. Exit the Properties dialog. You will probably find a few more sliders there than you did before. The Line In slider controls the amount of Line In that gets fed to your speaker. This is independent of what goes to your recorder app. Now go back to Properties, select Record controls, and once again check all the checkboxes. Exit the Properties dialog; you are now looking at Record controls. Now you get a list of available input sources and their adjustments. This list is list is slightly different depending on your sound card. If you want to record from line, be sure the Line In is selected -- or not muted, depending on your sound card. The Line In level here controls the amount of Line In that gets to your recording. (And to avoid unnecessary noise, turn down to zero, or mute, or deselect all the other Record controls.) Same basic idea applies also to the microphone input and other recording sources.
Almost all PC soundcards have integrated MIDI interface functions to their joystick port. The joystick port only provides a way to get the MIDI serial data in TTL level from the card and to the card. The data must be converted to MIDI interface current loop using some external electronics (minumun is few resistors and one optoisolator).
Audio Modem Riser (AMR) is an Intel specification created with the aim to "make integration of audio/modem functions on to the motherboard easier by separating the analog I/O functions to a riser card for the desktop platform. Audio/Modem Riser (AMR) and Mobile Daughter Card (MDC) new modular specifications make integration of audio/modem functions on to the motherboard easier by separating the analog I/O functions to a riser card for the desktop platform, or a daughter card for mobile. The new AMR specification defines a hardware scaleable OEM (Original Equipment Manufacturer) motherboard riser board and interface, which supports both audio and modem.
Modern operating systems (Windows, Linux etc.) provide a quite useful API for programming soundcards. Nowadays you don't need to do low level programming to access soundcards (like you needed to do years ago with DOS system).
The normal way of outputting audio is to open a device and writing blocks of data to this device. How this exactly works depends on the OS. The audio data is generally written to output buffer. The output buffer is a block of memory which has several constrictions (on a PC, do not no about other hardware) the data in this buffer is usually transfered to the soundcard using the DMA controller. The DMA controller is a device which can copy data between memory and hardware devices without needing the CPU.
Please note that in many operating systems audio devices are opened exclusively. If another program tries to open the device when it is already open, an error is returned. Sound input works generally in the same way as the output (just in opposite direction).
In Windows, a program should refrain from directly reading and writing hardware ports on a sound card. Whenever possible, a program should instead call functions in the Windows operating system, which will do the actual hardware reading and writing for you (in conjunction with the sound card's Windows device driver). For writing data to the card, you pass that data to an operating system function that sends that data to the card's device driver, which in turn writes that data to the card.
In this way, you'll create a Windows program that will operate under many version versions of Windows and work with a wide range of sound cards and MIDI interfaces. It's the driver that has the hardware specific code in it, not your program.
There a "standard" that all Windows sound/MIDI drivers are written to follow. This is called Windows "Media Control Interface" (ie, MCI). The Windows MIDI Mapper, the MCI Sequencer Device (driver), and the MCI Wave Audio Device (driver) are 3 parts of MCI that are particularly relevant to sound/MIDI cards.
Nowadays there is also an another alternative sound API available. It is called DirectSound. DirectSound is part of APIs provided by Directx system.
Usually the simplest way to record audio data in UNIX system is to use normal UNIX commands such as cat or dd. For example cat /dev/dsp > xyz records data from the audio device to a disk file called xyz until the command is killed (ctrl-C). Command cat xyz > /dev/dsp can be used to play back the recorded sound file. (Note that you may need to change recording source and level using a mixer program before recording to disk works properly). NOTE: The name of the audio device can vary between different UNIX systems.
In UNIX systems Audio devices are always opened exclusively. If another program tries to open the device when it is already open, the driver returns immediately an error (EBUSY).
Soundcard low level programming is needed if you write sound card software for DOS or similar operating systems without sound APIs. If your operating system supports sounds, it is the preferred way to do this.
