doc.: ieee 802.11-04/1458r0 submission november 2004 miki et al., sharp slide 1 jitter requirements...

doc.: IEEE 802.11-04/1458r0

Submission

November 2004

Miki et al., Sharp

Jitter Requirements

Morgan Hirosuke [email protected]

Yoshihiro [email protected]

John [email protected]

doc.: IEEE 802.11-04/1458r0

Submission

November 2004

Miki et al., Sharp

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 4s 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

Octets 1

Element ID

1 1

Length

Octets 1

Element ID

1 1

Most Significant Octet Least Significant Octet

1

Synchronization presentation: 11-04-775

doc.: IEEE 802.11-04/1458r0

Submission

November 2004

Miki et al., Sharp

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 1s, 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 216 -1 microseconds, and the smallest precision that is sent is 0.15 nanoseconds.

Octets 1

Integer mostsignificant octet

1 1 1

Integer leastsignificant octet

Most significant Fraction of 1s

Least significant Fraction of 1s

Integer part Fractional part

Implied binary point

doc.: IEEE 802.11-04/1458r0

Submission

November 2004

Miki et al., Sharp

What is sampling Jitter in an audio system ?

Sampling with jittered clock

DAC ampclock

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

doc.: IEEE 802.11-04/1458r0

Submission

November 2004

Miki et al., Sharp

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 t

he tone.

doc.: IEEE 802.11-04/1458r0

Submission

November 2004

Miki et al., Sharp

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.

doc.: IEEE 802.11-04/1458r0

Submission

November 2004

Miki et al., Sharp


• 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.

doc.: IEEE 802.11-04/1458r0

Submission

November 2004

Miki et al., Sharp

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 TransportSerial

AES/EBU dataPLL clock

data

DAC amp

IF jitterSampling

jitter

Variations on power supply

amplifiernon-linearity

Jittercomponentevaluation

doc.: IEEE 802.11-04/1458r0

Submission

November 2004

Miki et al., Sharp


• 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.

doc.: IEEE 802.11-04/1458r0

Submission

November 2004

Miki et al., Sharp

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.

doc.: IEEE 802.11-04/1458r0

Submission

November 2004

Miki et al., Sharp

Jitter requirements - summary

10us 3us 500ns 250ns 50ns 25ns 10ns 1ns

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

doc.: IEEE 802.11-04/1458r0

Submission

November 2004

Miki et al., Sharp

How to remove jitter ? – use RX buffer fullness

802.11nMAC/PHY

802.11nMAC/PHY

MAC/PHYTX buffer

Audio/video interface

Adjust the output rate

by looking forthe fullness

of the RX bufferThis method introducea large amount of output jitter

doc.: IEEE 802.11-04/1458r0

Submission

November 2004

Miki et al., Sharp

How to remove jitter ? – use TSF timer

802.11nMAC/PHY

802.11nMAC/PHY

TSF timer( 1us precision )

MAC/PHY

Timestamp

Timetone

Timetone

+ delay

TX buffer


TSF timer( 1us precision )

We can achieve low performancedue to low precision and low frequency

of the time tone signal

doc.: IEEE 802.11-04/1458r0

Submission

November 2004

Miki et al., Sharp

How to remove jitter ? – use Sharp’s proposal

802.11nMAC/PHY

802.11nMAC/PHY

High granularity timer( 50ns precision )

MAC/PHY

Timestamp

Timetone

Timetone

+ delay

PLL

TX buffer


High granularity timer( 50ns precision )

We can achieve high performancedue to high precision and high frequency

of the time tone signal

doc.: IEEE 802.11-04/1458r0

Submission

November 2004

Miki et al., Sharp

Jitter requirements & solutions

10us 3us 500ns 250ns 50ns 25ns 10ns 1ns

1s 10s

1sUse

Sharp’s proposal

Use TSF timer

General market< $1000

High end market > $10000

10s 40s

Jittervalue

[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

doc.: IEEE 802.11-04/1458r0

Submission

November 2004

Miki et al., Sharp

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.

doc.: IEEE 802.11-04/1458r0

Submission

November 2004

Miki et al., Sharp

Sound propagation from 2 speakers

Left speaker Right 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

doc.: IEEE 802.11-04/1458r0

Submission

November 2004

Miki et al., Sharp

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)

[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 12th 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).

doc.: ieee 802.11-04/1458r0 submission november 2004 miki et al., sharp slide 1 jitter requirements...

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