Audio Performance and Feature Requirements

This section summarizes the required performance and features for audio on PC 98 systems.

Several companies have joined together to develop a standardized testing procedure for measuring audio performance titled “Personal Computer Audio Quality Measurement Definitions,” available on the web site at http://www.crystal.com/new/papers/meas.htm. Contributors to this specification include Audio Precision, Compaq Computer Corporation, Crystal Semiconductor, Intel Corporation, and Microsoft Corporation. Microsoft test procedures are based on this methodology and are available at http://www.microsoft/com/hwtest/.

3. Audio performance meets PC 98 requirements
Required

The following table summarizes audio performance requirements for all audio-enabled PC 98 systems, with the exceptions noted for mobile audio.

The tests isolate half-duplex play or record performance. Additional attention should be paid to full-duplex systems with an embedded microphone and speakers, such as mobile PCs and multimedia monitors, where acoustic coupling can significantly degrade microphone performance.

For precise definitions of the terminology used in the following charts, please refer to the test methodology paper at http://www.microsoft/com/hwdev/devdes/, as described earlier in this section.

PC 98 Audio Performance Requirements
Feature Requirement
Playback
performance
(PC-D-A) for line output		 Frequency response (-3 dB)
44.1-kHz source material
48.0-kHz source material

Dynamic range (SNR)

THD+N
20 Hz to 17.6 kHz4
20 Hz to 19.2 kHz4

≥80 dB FS A1,2

≤–60 dB FS A3
Recording performance
(A-D-PC) for line input		 Frequency response
44.1-kHz destination material
48.0-kHz destination material

Dynamic range (SNR)

THD+N
20 Hz to 17.6 kHz4
20 Hz to 19.2 kHz4

≥75 dB FS A2

≤–55 dB FS A3
Analog
pass-through performance
(A-A)		 Line input to line output
Frequency response (-3 dB)
Dynamic range (SNR)
THD+N

Line input to speaker output
with 8-ohm load
Frequency response (-3 dB)
Dynamic range (SNR)
THD+N

Microphone input to line output
Frequency response (-3 dB)
Dynamic range (SNR)
THD+N
20 Hz to 20.0 kHz4
≥80 dB FS A2
≤–60 dB FS A3



20 Hz to 20.0 kHz4
≥70 dB FS A2
≤–50 dB FS A3


100 Hz to 12.0 kHz
≥70 dB FS A2
≤–50 dB FS A3
Full-scale input voltage FSIP (A-D-PC) line input

FSIP (A-D-PC) microphone input

 1.0 to 2.0 Vrms

50 to 200 mVrms
Full-scale output voltage FSOP (PC-D-A) 1.0 to 2.0 Vrms
Line output cross-talk Channel separation between output channels (for example, left to right, center to right) ≥55 dB
Sampling frequency accuracy Playback

Record

 0.1%

0.1%
1Decibels relative to full scale (FS), measured using “A weighting” filters.

2For mobile PCs, the dynamic range requirements are relaxed by10 dB FS A.

3For mobile PCs, the THD+N requirements are relaxed by 10 dB FS A.

4For mobile PCs, the required frequency response is 20Hz to 15kHz, measured using 6 dB corners.

4. Audio system provides support for basic data formats
Required

The audio system must provide full-duplex support of the following audio formats:

The audio system must provide support for both recording and playing back of sample rates that include 8, 11.025, 16, 22.05, 44.1, and 48 kHz.

5. Audio system reports sample position for stream synchronization

Required

The driver must be capable of returning an accurate indication of the current position of the buffer being rendered. Sample accuracy is in relation to the samples given to the codec. Accurate reporting of the current position in the buffer being rendered means reporting the position within 1 ms. This requirement applies for both compressed and uncompressed data.

For information about WDM device driver support for streaming capabilities, see the Windows NT 5.0 DDK. See also the related articles available on the web at http://www.microsoft.com/hwdev/pcfuture/.

6. Audio system provides sufficient externally accessible inputs and outputs
Required

At a minimum, the audio system must have the following features:

  • A monaural microphone, stereo line input, or both

  • Stereo line-level output

These inputs and outputs can be located anywhere on the system, including on the speakers and video monitor.

7. Audio system connectors are labeled with icons as defined for PC 98

Required

To reduce user confusion, the external connections must use a consistent set of symbols based on the standard artwork defined in the “Icons” appendix in the References part of this guide.