1. doc.: IEEE 802.11-04/1458r0 Submission November 2004 Miki et al., Sharp Slide 1 Jitter Requirements Morgan Hirosuke Miki miki@slab.tnr.sharp.co.jp Yoshihiro Ohtani ohtani@slab.tnr.sharp.co.jp John Kowalski kowalskj@sharplabs.com

2. doc.: IEEE 802.11-04/1458r0 Submission November 2004 Miki et al., Sharp Slide 2 Sharp’s Proposal: Optional Support for Link Synchronization: Capability Advertisement The format of this element is a non-negative integer representation whose value, if given by Synchronization Precision, communicates that the achievable synchronization is 4  s X 2 -SynchPrecision. When the value of SynchPrecision is 0, MSDU TimeStamps are not transmitted from an 802.11n station. This allows STAs to associate with APs and establish streams to STAs that match supported synchronization capability to the application. Synchronization Capability Element Synchronization presentation: 11-04-775

3. doc.: IEEE 802.11-04/1458r0 Submission November 2004 Miki et al., Sharp Slide 3 Sharp’s Proposal: Optional Support for Link Synchronization: Timestamp for Link Synchronization The TLS is a 4 octets time stamp updated by the clock of the STA transmitting the aggregated frame. The two most significant octets are integers. The least significant two octets are in fractional units of 1  s, i.e., the most significant bit of the most significant octet of the Fractional part is ½ microsecond, the next most significant bit of the most significant octet of the Fractional part is ¼ microsecond and so forth. By transmitting this way, the maximum value of the integer part is 2 16 -1 microseconds, and the smallest precision that is sent is 0.15 nanoseconds. Octets1 Integer most significant octet 111 Integer least significant octet Most significant Fraction of 1  s Least significant Fraction of 1  s Integer part Fractional part Implied binary point

4. doc.: IEEE 802.11-04/1458r0 Submission November 2004 Miki et al., Sharp Slide 4 What is sampling Jitter in an audio system ? Sampling with jittered clock DACamp clock data Sampling jitter is the variation in the clock timing for the audio signal in ADC, DAC, or asynchronous sample rate converter (ASRC). Ideal sampling

5. doc.: IEEE 802.11-04/1458r0 Submission November 2004 Miki et al., Sharp Slide 5 How does sampling jitter affect the audio signal ? The amplitude of the sampling jitter modulation products is proportional to –the amplitude of the sampling jitter, and –the rate of change of the signal that is being affected by the jitter. For an audio tone of frequency f and sinusoidal sampling jitter of peak amplitude J the modulation sidebands produced are at a relative level (with respect to the audio tone) of 20 log(  fJ), which is derived in paper [1]. –For example, with sinusoidal jitter of 10ns rms (14ns peak) on a 1kHz tone the level of each sideband will be -87dB. –The same jitter on a 10kHz tone will be at -67dB with respect to the tone.

6. doc.: IEEE 802.11-04/1458r0 Submission November 2004 Miki et al., Sharp Slide 6 What is the requirement for sampling jitter ? Paper [2] describes practical research that found the lowest sampling jitter level at which the jitter made a noticeable difference to be about 10ns rms. This was with a high level test sine tone at 17kHz. With music none of their subjects found sampling jitter below 20ns rms to be audible.

7. doc.: IEEE 802.11-04/1458r0 Submission November 2004 Miki et al., Sharp Slide 7 What is the requirement for sampling jitter ? If the sampling jitter is not composed by a single sinusoidal wave, but composed by lots of frequencies ( such as white noise ), then the requirements for the sampling jitter becomes less stringent. Paper [4] evaluates the requirements for white noise sampling jitter, and concludes that no one detected the sampling jitter below 250ns.

8. doc.: IEEE 802.11-04/1458r0 Submission November 2004 Miki et al., Sharp Slide 8 Where to evaluate jitter? Jitter is typically evaluated by sampling jitter on DAC. AES/EBU IF jitter may increase sampling jitter on DAC. Papers [3] evaluates the jitter components in the output sound from speakers, so that they can estimate the amount of jitter with what we hear, which includes the variations of DAC power supply or the effect of non-linearity characteristics of the amplifier. CD Transport Serial AES/EBU data PLL clock data DACamp IF jitter Sampling jitter Variations on power supply amplifier non-linearity Jitter component evaluation

9. doc.: IEEE 802.11-04/1458r0 Submission November 2004 Miki et al., Sharp Slide 9 What is the requirement for sampling jitter ? Paper [3] evaluates the jitter components at the output signal that are included in the current high end audio systems. It concludes that most of the current high end audio systems includes jitter components less than 1ns.

10. doc.: IEEE 802.11-04/1458r0 Submission November 2004 Miki et al., Sharp Slide 10 Requirements from specifications MPEG2 specification specifies that the PCR accuracy should be less than 500ns. IEEE 1394 specification isochronous interface is designed so that it can eliminate jitters in 50ns level.

11. doc.: IEEE 802.11-04/1458r0 Submission November 2004 Miki et al., Sharp Slide 11 Jitter requirements - summary 10us3us500ns250ns50ns25ns10ns1ns General market < $1000 High end market > $10000 Jitter value [3] Jitter components included in current high end audio system [6] A few people detects 10ns [4] Req. for white noise jitter [3] thinks the jitter req. is less than [4] Req. from MPEG2 Req. from IEEE 1394 spec[2] Below 20ns rms are not audible

12. doc.: IEEE 802.11-04/1458r0 Submission November 2004 Miki et al., Sharp Slide 12 How to remove jitter ? – use RX buffer fullness 802.11n MAC/PHY 802.11n MAC/PHY TX buffer Audio/video interface Adjust the output rate by looking for the fullness of the RX buffer This method introduce a large amount of output jitter

13. doc.: IEEE 802.11-04/1458r0 Submission November 2004 Miki et al., Sharp Slide 13 How to remove jitter ? – use TSF timer 802.11n MAC/PHY 802.11n MAC/PHY TSF timer ( 1us precision ) MAC/PHY Time stamp Time tone Time tone + delay TX buffer Audio/video interface TSF timer ( 1us precision ) We can achieve low performance due to low precision and low frequency of the time tone signal

14. doc.: IEEE 802.11-04/1458r0 Submission November 2004 Miki et al., Sharp Slide 14 How to remove jitter ? – use Sharp ’ s proposal 802.11n MAC/PHY 802.11n MAC/PHY High granularity timer ( 50ns precision ) MAC/PHY Time stamp Time tone Time tone + delay PLL TX buffer Audio/video interface High granularity timer ( 50ns precision ) We can achieve high performance due to high precision and high frequency of the time tone signal

15. doc.: IEEE 802.11-04/1458r0 Submission November 2004 Miki et al., Sharp Slide 15 Jitter requirements & solutions 10us3us500ns250ns50ns25ns10ns1ns 1s10s 1s Use Sharp’s proposal Use TSF timer General market < $1000 High end market > $10000 10s40s Jitter value [3] Jitter components included in current high end audio system [6] A few people differentiate 10ns 1min* [4] Req. for white noise jitter [3] thinks the jitter req. is less than [4] Req. from MPEG2 Req. from IEEE 1394 spec[2] Below 20ns rms are not audible Time to converge Use buffer fullness 20min 1h ? * Utilizes 1PPM clock

16. doc.: IEEE 802.11-04/1458r0 Submission November 2004 Miki et al., Sharp Slide 16 Regarding the requirements by Dolby UK … It seems that Dolby UK engineers comment about 1ms time difference in the speaker drivers… Our conclusion is that this is NOT a jitter requirements, since we could not find any documents mentioning that jitter should be 1ms. It seems for us that Dolby is saying some requirement for the difference of sound propagation delays for multiple speakers.

17. doc.: IEEE 802.11-04/1458r0 Submission November 2004 Miki et al., Sharp Slide 17 Sound propagation from 2 speakers Left speakerRight speaker Sound speed: about 30cm in 1ms Time sound in the air 1 2 sound in 1 (meddle point) Time sound in the air sound in 2 from left and right speaker from left speaker from right speaker

18. doc.: IEEE 802.11-04/1458r0 Submission November 2004 Miki et al., Sharp Slide 18 References [1] Julian Dunn, “Considerations for Interfacing Digital Audio Equipment to the Standards AES3, AES5, AES11”, Published in `Images of Audio', the Proceedings of the 10th International AES Conference, London, September (1991), pp 115-126. [2] Eric Benjamin and Benjamin Gannon, “Theoretical and Audible Effects of Jitter on Digital Audio Quality”, Pre-print 4826 of the 105th AES Convention, San Francisco, September (1998) [3] Akira Nishimura and Nobuo Koizumi: “Various Aspects and Factors of Sampling Jitter Observed in Digital Audio Products” http://www.iic.tuis.ac.jp/edoc/journal/ron/r7-2-8/index.html (Japanese) http://www.iic.tuis.ac.jp/edoc/journal/ron/r7-2-8/index.html [4] S. Kiryu, K. Ashihara, S. Yoshikawa, M. Sawaguchi, T. Ohga: “An Discrimination Experiment of Distortion Due to Time Jitter on PCM Musical Signal for Various Subjects”, Technical report of IEICE EA2002-36 (2002-6), pp35-38 [5] Akira Nishimura and Nobuo Koizumi, “Measurement of sampling jitter in analog- to-digital and digital-to-analog converters using analytic signals”, Proceedings of the 12 th Audio Engineering Society Convention, No. 5558, 1-6 (2002). [6] Hisao Sakai, “Perceptibility of Wow and Flutter”, Jornal of Audio Engineering Society, 18, 290-298, (1970).