Slide 1
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]
Slide 2
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
Slide 3
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
Slide 4
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
Slide 5
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.
Slide 6
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.
Slide 7
doc.: IEEE 802.11-04/1458r0
Submission
November 2004
Miki et al., Sharp
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.
Slide 8
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
Slide 9
doc.: IEEE 802.11-04/1458r0
Submission
November 2004
Miki et al., Sharp
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.
Slide 10
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.
Slide 11
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
Slide 12
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
Slide 13
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
Audio/video interface
TSF timer( 1us precision )
We can achieve low performancedue to low precision and low frequency
of the time tone signal
Slide 14
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
Audio/video interface
High granularity timer( 50ns precision )
We can achieve high performancedue to high precision and high frequency
of the time tone signal
Slide 15
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
Slide 16
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.
Slide 17
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
Slide 18
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).
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