Advanced Audio Recommendations

This section outlines the future direction of PC audio. It offers a view of the market requirements to come for PC audio, describing a number of directions that the industry is taking.

8. Audio performance meets PC 98 advanced recommendations
Recommended

The expectations for audio quality in the consumer-electronics industry are quite high. For those applications where audio quality is important, such as for Entertainment PC, it is strongly recommended that audio performance meet the capabilities recommended in the following table.

PC 98 Audio Performance Recommendations
Feature Recommendation
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 20 kHz
20 Hz to 20 kHz

≥85 dB FS A

≤–65 dB FS A
Recording
performance
(A-D-PC)
for line input		 Frequency response (-3 dB)
44.1-kHz destination material
48.0-kHz destination material

Dynamic range (SNR)

THD+N
20 Hz to 20 kHz
20 Hz to 20 kHz

≥80 dB FS A

≤–60 dB FS A
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
with 8-ohm load
Frequency response (-3 dB)
Dynamic range (SNR)
THD+N
20 Hz to 20.0 kHz
≥85 dB FS A
≤–65 dB FS A


20 Hz to 20.0 kHz
≥75 dB FS A
≤–55 dB FS A



20 Hz to 20.0 kHz
≥75 dB FS
≤–55 dB FS
Full-scale
input voltage		 FSIP (A-D-PC) line input

FSIP (A-D-PC) microphone input

 2.0 to 3.0 Vrms

50 to 200 mVrms
Full-scale
output voltage		 FSOP (PC-D-A) 1.0 to 2.0 Vrms
Cross talk between signal channels Stereo separation ≥65 dB A
Sampling frequency accuracy Playback

Record

 0.1%

0.1%

9. Audio system supports full-duplex operation at independent sampling rates
Recommended

Voice recognition and audio/video conferencing require the audio system to simultaneously play back and record. Incoming and outgoing audio should be capable of operating at independent sampling rates. This recommendation considers the entire system, including the possibility of USB speakers or microphones.

10. Audio system provides hardware or software support for the Downloadable Samples specification
Recommended

Support for DLS as defined by the MIDI Manufacturers Association is recommended. For more information, see DLS Specification, Version 1.0 or higher, at http://www.midi.org.

11. Audio system supports AEC reference inputs
Recommended

Full-duplex internal or external audio codecs that introduce additional digital or analog audio sources into the final mix are recommended to support simultaneous capture of microphone and AEC reference inputs. One analog-to-digital converter (ADC) is used to capture the microphone input, and another ADC is used to capture a monophonic representation of final output mix, which includes all digital and analog sources.

It is possible to use a single stereo ADC to capture the two monaural streams. The AEC reference should be time-synchronized and available at the same sample rate as the microphone input.

For more information, see Section 6.2 of the Audio Codec ’97 specification from Intel Corporation, which describes one possible implementation.

12. Audio system provides hardware filtering of HRTF 3-D filters
Optional

For those solutions that provide hardware acceleration of 3-D filters, support for eight separate audio sources is suggested, especially for Entertainment PCs.

13. CD, DVD, and broadcast audio playback meet PC 98 requirements
Required with DVD Video

These recommendations are specified to ensure quality playback of MPEG-2 audio from any source, including DVD, digital broadcast or satellite systems, hard drives, and so on. The goal for DVD and other A/V playback is to ensure that the end-user experience is the same or better than from a stand-alone DVD player.

For those PCs that support software or hardware decoding and playback of DVD-Video or MPEG-2 video, the audio decoder must be capable of supporting the following formats:

  • Support for one or both of the following formats is required, depending upon the local requirements for DVD audio:

  • AC-3 (Dolby Digital) less than or equal to 5.1 channels, at 48 kHz less than or equal to 384 Kbps.

  • MPEG-2 multichannel less than or equal to 7.1 channels, at 48 kHz less than or equal to 912 Kbps.

  • MPEG-1 Layer 2 stereo, at 44.1 and 48 kHz less than or equal to 384 Kbps.

  • LPCM less than or equal to 8 channels, 16-bit, 20-bit, and 24-bit at 48 or 96 kHz less than or equal to 6.144 Mb/s.

Note: Conversion to 48-kHz 16-bit stereo is acceptable when the content exceeds the available resolution, sampling rates, or number of output channels.

14. Audio system provides consistent volume levels for different devices

Optional

In cases where each audio channel is set to the same position on the Windows mixer panel, it is suggested that each channel provide a comparable volume level. Users should not need to have radically different settings on the control panel to balance the relative volume of each audio channel.