generate jitter test signal and measurign jitter using AP2?

[BJAMR]

HI,

I have access to an Audio Precision System 2 (with DSP), is there a way that I can create a special signal and record it on a CDR, then use it to test the jitter of my CDplayer?

[Rookie]

Here is atached a 16bit/44.1kHz JTEST signal. It is composed of a 11025Hz -6.02dB square wave toggled with 229.6875Hz LSB. Duration is 35s.

[BJAMR]

Thanks.

Once I burn this to a CDR, I just run a FFT sprectrum analysis against the output of my CD player, correct?

Any other settings/set-up I need to be aware of?

Thanks again.

[atalio]

I hope Rookie responds to your question more fully, but in my experience with this type of jitter test signal, the FFT window type plays an important role in determining the noise floor and response characteristics. While this is true of any FFT test, it is of particular concern in this type of test. You may also want to use larger FFT sizes.

You will need to convert the dB output to picoseconds of jitter. I believe one of Julian Dunn's articles may contain the necessary formula.

Because differences in measurement techniques are possible, you should exercise caution before making any comparisons to measurements performed by others.

[Rookie]

You can find more about jitter measurements in Julian Dunn's book "Measurement Techniques for Digital Audio". It can be downloaded here .
Also here is how Pedja Rogic did jitter measurements of his DAC:

ASR Measurements
AR Measurements2

[janneman]

Hi Rookie,

May I pick your brain; can you tell me if I could use this test equipment to measure CD digital signal jitter?

"The Digital Transmission Analyzer ME520A measures digital errors of bit rates from 1 kbit to 150 Mbit/s (maximum 170 Mbit/s with Option 02), and digital timing jitter of clock frequencies from 700 kHz to 150 MHz (maximum 170 MHz with Option 02).
This analyzer is ideal for development and maintenance of 1st to 4th order digital line transmission systems, digital radio transmission systems and digital optical transmission systems, including the 10CH system of the PCM 30CH system (CEPT).
The input/output interface conforms to CCITT Rec. G.703, the pseudo-random pattern conforms to CCITT Rec. O.151, and jitter measurement conforms to CCITT Rec.O.171.
The ME520A consists of a transmitter and a receiver. End-to-end and loop-back tests can be performed with one ME520A. The transmitter can output pseudo-random (PRBS 2 exp.10-1, 2 epx 15-1, 2 epx.23-1), 1 to 16 bit variable length programmable words, and 2 x 8 bit alternate word patterns as NRZ an RZ unipolar signals, AMI and HDB3 bipolar signals, and in CMI signal formats. Bit and code error addition, internal clock frequency offset, and jitter modulation by external signals are possible by adding functions.
The receiver can measure digital errors of unipolar, AMI, HDB3 and CMI signals. Jitter measurement is also possible with clock signals or code signals (clock regenerated internally). Digital error and jitter are simultaneously measured and analyzed and the results are displayed digitally. The measured results can be printed out with a built-in thermal printer (Option 01) and the results can be stored.
The GP-IB interface is standard with both the transmitter and the receiver unit. It is convenient for taking measurements automatically."

I have also more detailed descrition but it is too large a file to attach to the posts; I could mail it to you.

Thanks,

Jan Didden

[Bernhard]

Originally posted by BJAMR
HI,

I have access to an Audio Precision System 2 (with DSP), is there a way that I can create a special signal and record it on a CDR, then use it to test the jitter of my CDplayer?

Perhaps use it to measure the low level linearity of the DAC, this is what makes the digital sound.

[nemestra]

Originally posted by janneman
Hi Rookie,

May I pick your brain; can you tell me if I could use this test equipment to measure CD digital signal jitter?

"The Digital Transmission Analyzer ME520A <snip>
Jan Didden

Hi Jan,

ok, I'm not Rookie, but I'm familiar with jitter measurements on the AP2 and with the ME520A.

ME520A is a nice piece of gear. It used to be one of my favourites for measuring PDH interfaces in telecoms. It is reliable, flexible and gives repeatable results (unlike some of the HP/Agilent) gear. Out of the hundreds of bits of test gear for jitter measurement at my disposal at my last job it was one of the better ones.

They often come up for sale for peanuts these days. I've been offered mint condition RX/TX pairs with the jitter modulator several times for less than 100 UK pounds.

BUT there no point if you're not interested in telecoms, specifically PDH (G.703) interfaces. They will not work at non-telecoms frequencies and will not generate or lock to any audio signal (44k1, 48k, 96k etc.) They don't understand SPDIF or AES or any other variant. Even if they did they only give an indication of the amount of jitter (pk-pk UI). For the modifier/designer a single jitter number is not of much use. The jitter spectrum is of much more interest.

I don't think that they would be easily mod'ed to do audio. Still some of the internal parts such as pulse transformers may be marginally useful and if you like 19" rack case they are quite sturdy.

Overall, don't bother.

James

[janneman]

Thanks James, that was quite usefull.

have a nice day,

Jan Didden

[percy]

are there any jitter measurement AND listening tests that have ever been done to demonstrate at what point jitter starts causing audible artefacts ? Please direct me to some, if any.
I see numbers thrown around (X picosecs or Y nanosecs) and the race to achieve extremely low jitter in the range of double digit picoseconds but I am really interested in finding out where really is that point of diminishing returns ?