Before you start to program, you should familiarize yourself with your workstation's audio hardware and the peripherals with which you will be working. This chapter describes the audio capabilities and the audio I/O interfaces available on IRIS Indigo, Indigo2, and Indy workstations. This chapter also provides recommendations for minimal and optimal configurations of memory, hard disk, and other peripherals useful for audio development and testing.
See Appendix A, “Audio Specifications,” and your workstation owner's guide for complete details on audio hardware features. See the online release notes for audiodev, the audio development environment of the IRIS Media Libraries, for information about system software requirements.
The standard audio hardware supplied with Indigo workstations supports 24-bit digital stereo and 16-bit analog stereo sound. A dedicated real-time processor works in tandem with the CPU to ensure that audio timing isn't degraded by other system demands.
Indigo audio features include:
built-in speaker
stereo line-level analog input and output
stereo headphone output
microphone input with phantom power
AES/EBU digital audio input and output
sampling rates include 8000, 11025, 16000, 22050, 32000, 44100, and 48000 Hz.
independent input and output rates
output rate can be synchronized to the digital input rate
low-latency operation for highly interactive applications
The audio hardware interface on the back panel of Indigo workstations includes these 3.5-mm audio input and output jacks, which are labeled with icons (see Figure 4-1):
monaural microphone input jack for mic-level audio input
stereo line-level input (line in) jack for analog audio input from a tape deck, CD player, or similar source
stereo line-level output (line out) jack for analog audio output, for example, to a tape deck or amplifier
stereo headphone output jack
stereo digital I/O jack for digital audio input and output
An internal switching mechanism selects one active input source from the three available inputs. All three outputs are always enabled; each transmits a copy of the same output signal, but the volume is adjusted on the headphone/speaker output. Using the headphone jack preempts output to the internal speaker, which normally outputs the sum of the left and right signals.
Digital input and output signals are simultaneously transmitted over a stereo cable. The Audio Engineering Society (AES) standard supports mono and stereo streams of 20-bit or 24-bit samples. Each of the digital input and output streams contains two interleaved channels (left and right) of audio samples.
Figure 4-2 shows the location of the audio jacks on the back panel of the Indigo workstation.
The audio hardware supplied standard with the Indigo2 and Indy workstations provides the same basic audio capabilities as that of the Indigo workstation, plus:
The audio hardware interface on Indigo2 and Indy workstations includes these 3.5-mm audio input and output jacks (see Figure 4-3 for the Indigo2 back panel layout, and Figure 4-5 for the Indy back panel layout):
microphone/line-in2 jack for mono and stereo mic-level audio input
stereo line-in jack for analog audio input from a tape deck, CD player, or similar source
stereo line-out jack for analog audio output, for example, to a tape deck or amplifier
stereo headphone/line-out2 output jack
stereo digital in/out jack for digital audio input and output
As in the Indigo workstation, all three outputs are enabled, and an internal switching mechanism selects one active input source from the three available inputs. In addition, a software-controllable internal switching mechanism permits 4-channel audio I/O through the standard I/O interface. See “4-channel Audio I/O Interface” for details on
4–channel audio.
Figure 4-3 shows the location of the audio jacks on the back panel of the Indigo2 workstation.
The Indy workstation features a slightly different layout for its audio I/O interface. Two triangular pushbuttons on the front of the Indy workstation let you adjust the volume of the internal speaker/headphone output up or down, as desired. Pressing both buttons at the same time mutes the speaker/headphone output.
Figure 4-4 shows the volume control buttons on the front of the Indy workstation.
Figure 4-5 shows the location of the audio jacks on the back panel of the Indy workstation.
A software-controllable internal switching mechanism permits 4-channel audio I/O through the standard I/O interface. When a system is operating in 4-channel mode, the electrical properties of the microphone jack can be configured to accept either line-level or mic-level input, and the electrical properties of the headphone jack can be configured to produce line-level output.
Figure 4-6 shows an Indy workstation cabling setup for 4-channel audio.
Cables like the ones shown in Figure 4-6 can be purchased from audio accessory dealers. One end of the cable has 3.5-mm audio plugs that plug into the Indigo2 or Indy workstation jacks; the other end independently terminates each of the two independent signals with RCA phono plugs.
 | Note: Do not confuse these cables with “Y” connectors that route the same signal to multiple connections. |
When the system is configured (either from apanel or from the Audio Library) to use 4-channel mode, (L1, R1) samples are input to the line-in jack and (L2, R2) samples are input to the microphone/line-in2 jack. Similarly, in 4-channel mode, (L1, R1) samples are output from the line-out jack, and (L2, R2) samples are output from the headphone/line-out2 jack.
The primary considerations in setting up your system for digital audio software development are memory and disk space. Because of the large sizes of audio sample files, disk space in particular is crucial.
A minimum of 32 MB is recommended for digital audio development. The more memory installed, the more responsive your workstation will be when handling large amounts of sample data, as well as during compilation.
Be sure to allow an adequate amount of disk space. These statistics should help give you an idea of the kind of disk space required for your application:
mono 8-bit, CCITT/TSB G.711 μ-law encoded 8 kHz (speech quality) audio = 8 kBytes/sec
mono 16-bit (15-bit range, 14-bit resolution), CCITT/TSB G.722 compressed 16 kHz (high-quality speech with more computationally expensive compression) audio = 8 kBytes/sec
stereo 16-bit 44.1 kHz (CD-quality digitized analog input) audio = 176 kBytes/sec
stereo 24-bit 48 kHz (highest-quality digital, 4-byte word) audio = 384 kBytes/sec
4-channel 16-bit 44.1 kHz (CD-quality digitized analog input) audio = 352 kBytes/sec
4-channel 24-bit 48 kHz (highest-quality digital, 4-byte word) audio = 768 kBytes/sec
A minimum of 600 MB is suggested; 800 MB or more is recommended, especially if your development work involves storing large amounts of high-quality sample data on disk.
If you do not already have a CD-ROM drive, you may want to purchase one. Prosonus®, Aware®, Inc., and other companies supply CD-ROM libraries of audio sample data (see “Third-party Audio Software and Sound Libraries” in Chapter 5 for information on ordering these CD-ROM libraries). You can also use the drive for sampling from audio CDs (obtain permission before using copyrighted material).
A DAT drive is recommended both for general data archiving and for transferring audio from hard disk.