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Author Topic: AKM AK5393  (Read 7879 times)

Schallfeldnebel

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AKM AK5393
« on: October 30, 2006, 11:20:36 am »

My Lake-People AD converters have the AKM AK5393 AD converterchips on board. Because an upgrade was made in this system from AK5392 (only 44-48k)to AK5393 (96k) it was not possible to have both 44-48k and 88-96k switchable for the oversampling. 64x for 96 and 128x for 48k. The change of oversampling is done within the software of the chip I understood.

Therefore my unit runs always on 64x, even when it is set to 44,1 mode. This effects the signal to noise ratio with about 3 dB less good values at 44,1K.

Are there other consequences ? Less precision ?

Erik Sikkema

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danlavry

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Re: AKM AK5393
« Reply #1 on: October 30, 2006, 01:40:31 pm »

Schallfeldwebel wrote on Mon, 30 October 2006 16:20

My Lake-People AD converters have the AKM AK5393 AD converterchips on board. Because an upgrade was made in this system from AK5392 (only 44-48k)to AK5393 (96k) it was not possible to have both 44-48k and 88-96k switchable for the oversampling. 64x for 96 and 128x for 48k. The change of oversampling is done within the software of the chip I understood.

Therefore my unit runs always on 64x, even when it is set to 44,1 mode. This effects the signal to noise ratio with about 3 dB less good values at 44,1K.

Are there other consequences ? Less precision ?

Erik Sikkema




Hi Erik,

I am not familiar with the AKM5392, nor do I have other details so I can not answer your question. One would have to know what OTHER changes and possible improvements were made inside the IC.

When one increases sample rate, while ALL OTHER FACTORS HELD CONSTANT, then there is a trade off between speed and accuracy.
But I am not sure that the AK5393 is an AK5392 operating at faster rate.

You can be sure that a 1990 state of the art AD chip is not going to be up to par with say a 2000 AD chip. There are a number of factors that count, including the IC process itself, as well as the architecture and circuit design.

My point about speed vs accuracy trade off does hold, when you keep all other factors equal. In other words, if you could convince the IC makers to take their existing process, use the same design architecture and capabilities, the design that complies with the OPTIMUM sample rate FOR AUDIO audio will yield best results.

Of course one can come up with a 2006 AD IC that will be better then say a 48KHz design from 1990. That does NOT mean that 384 is better then 48KHz or visa versa. There are too many variables here.

The real comparison should be between 2 designs of different sample rate speed, but with the SAME design team, the SAME IC process, the SAME level of technical expertize...

Unfortunately, the IC makers decided to accommodate a marketing driven 192KHz rate, instead of the optimal rate for audio (60 or 70KHz). So while some of the IC's are good, they could have been much better.  

Regards
Dan Lavry
http://www.lavryengineering.com
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Schallfeldnebel

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Re: AKM AK5393
« Reply #2 on: October 30, 2006, 02:36:41 pm »

Maybe I have been unclear, but my question is, what happens if a chip which is designed to run 128x oversampling for 44,1K is set to 64x oversmpling at 44,1k? Just to accomodate the possibility of recording 96K. At 96K the chip runs on a 64x oversampling.

/E
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danlavry

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Re: AKM AK5393
« Reply #3 on: October 31, 2006, 01:42:34 pm »

Schallfeldwebel wrote on Mon, 30 October 2006 19:36

Maybe I have been unclear, but my question is, what happens if a chip which is designed to run 128x oversampling for 44,1K is set to 64x oversmpling at 44,1k? Just to accomodate the possibility of recording 96K. At 96K the chip runs on a 64x oversampling.

/E


The answer to your question may be IC specific, but as a rule, I would expect the front end of an AD (the modulator) to operate at some fixed high frequency. In your case, the rate for 44.1KHz is 5.644MHz, and for 48KHz it is 6.144MHz. That coresponds to 128fs. Now, when you raise the sample rate to say 96KHz, the modulator can stay at 6.144MHz which is 64fs.

The main differance between 64fs and 128fs will be the back end of the AD (the decimator). In one case, the decimator converts the modulator output (few bits but at very high speed of 6.144MHz) to many bits at 48KHz (or 44.1KHz), in the other case, it "skips" the last "divide bt 2" decimation stage. The decimation is of course is synchronus sample rate down conversion.

The big differance between a 48K IC and 96K IC is in the front end. An IC made for say 48KHz, will be focused on clean usable audio range of 0-24KHz (well maybe 0-22KHz or so in practice).
An IC aimed at sat 192KHz will be designed to accomodate signals up to 96KHz (well maybe 93KHz or so).

So there is no way you could use a 48KHz to record signals above 24KHz. That region above 24KHz is "full of noise" by design. The noise shaping moves noise from under 24KHz to frequencies above 24KHz.

But an IC designed for 192KHz can record 96KH signals. If you wish to set such an IC to opertae at say 48KHz, it will remove the signals it recorded above 24KHz, and in theory yield the same results as the 48KHz IC.

But in practice, going to 192KHz does call for a performance reduction when all things are held equal. All things equal means the same modulator filter order, the same number of modulator bits, the same high frequency clock (such as 6.144MHz), the same IC process...

The amount of noise shaping - removal of noise from "signal bandwidth" (what is dedicated to audio) to the "noise bandwidth" (frequencies above the signal bandwidth) is fixed
for a given set of parameters.

This is analogous to a guy with a capability of dig say 9 cubic feet of dirt. You can ask the guy to dig a 1 foot square hole 9 feet deep. You can ask the hole to be 3 feet by 3 feet and 1 foot deep.

The qestion is then, do you want a "deep hole" for 24KHz of audio? A shallow hole for 96Khz of audio.

If you are willing to accept that we do not hear 90KHz, that our mics and speakers do not process 96KHz of audio, then keeping a wide range of say 96KHz (for 192KH sampling) is a waste. You could, for the same resources get a better 48KHz of audio, and even better performance at 24KHz of audio.

We know that 44.1KHz may be tight in some cases (mostly implementation issue). I view 96KHz sampling as already too high. The optimum is somewhere between 48 and 96KHz sampling, but the standards do not suport it.

Having said all the above, newer IC's often see impovments in many areas, from circuit design to process and more, so one can not assume that all things are equal. So a newer 96KHz IC many be better at 44.1KHz then an older 44.1KHz IC.

It is just too bad that due to the rush to accomodate higher sampling speed, the noise shaper is forced to accomodate a huge range that we do not use. The IC makers could do a better 96KHz IC, if they would agree to do away with 192KHz and apply the same capabilities they invested in 192Khz into a 96KHz IC.  

I know some of the above was somewhat off subject, but it does tie in to your question.

Regards
Dan Lavry
http://www.lavryengineering.com
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Schallfeldnebel

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Re: AKM AK5393
« Reply #4 on: October 31, 2006, 01:54:43 pm »

Dan, you write:"The answer to your question may be IC specific, but as a rule, I would expect the front end of an AD (the modulator) to operate at some fixed high frequency. In your case, the rate for 44.1KHz is 5.644MHz, and for 48KHz it is 6.144MHz. That coresponds to 128fs."

The manufacturer of my AD converter told me, instead of 128xfs, it runs on 64xfs at 44,1K, although it is designed to run 128x at 44,1K. Is that possible, and what are the consequences? Does it mean that the modulator runs on half the speed? 2.822Mhz? How could they change the modulator speed?

If I understand you well, and the modulators run fixed 5.644Mhz, and the fs is set to 44,1 you always run 128x oversampling.

The older IC's which ran indeed 64x at 44,1, did their modulator ran on 2.822Mhz.

What is the trade off for 2.822Mhz?

/E
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danlavry

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Re: AKM AK5393
« Reply #5 on: October 31, 2006, 03:25:01 pm »

Schallfeldwebel wrote on Tue, 31 October 2006 18:54

Dan, you write:"The answer to your question may be IC specific, but as a rule, I would expect the front end of an AD (the modulator) to operate at some fixed high frequency. In your case, the rate for 44.1KHz is 5.644MHz, and for 48KHz it is 6.144MHz. That coresponds to 128fs."

The manufacturer of my AD converter told me, instead of 128xfs, it runs on 64xfs at 44,1K, although it is designed to run 128x at 44,1K. Is that possible, and what are the consequences? Does it mean that the modulator runs on half the speed? 2.822Mhz? How could they change the modulator speed?

If I understand you well, and the modulators run fixed 5.644Mhz, and the fs is set to 44,1 you always run 128x oversampling.

The older IC's which ran indeed 64x at 44,1, did their modulator ran on 2.822Mhz.

What is the trade off for 2.822Mhz?

/E


I believe I said "as a rule". I am trying to be careful here to point out that one can not answer it all without familiarity of all the IC's in question.

As a rule (I am saying it again), I would expect a modulator to be designd to work at one speed (some speed range, because you need to accommodate possibly 32-50KHz, 88.2, 96 and so).
That is so because the noise shaping is fundamentally highly effected by the oversampling ratio (as well as modulator bits and filter order).
But I can see how one can cut the clock rate by 2 and get half the audio bandwidth out of it. Doing so may work well, it would yield longer time for the sample hold and the switch capacitor filters to charge, and for the amps to settle. But doing so may also cause problems, such as more time for the caps to leak between clocks...

So I really can not answer your question, without intimate knowledge of the AKM5392 (which I do not have).

Did you look at the specs of the IC's in question (running in both speeds)?

Regards
Dan Lavry
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Schallfeldnebel

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Re: AKM AK5393
« Reply #6 on: October 31, 2006, 05:07:06 pm »

The 5392 runs at 128x and only 44-48K, and the modulator runs the standard speed you before mentioned. There is nothing to fins about how that modulator speed could be cut to half.

The 5393 runs 128x at 44-48K and 64x at 88-96K. The same modulator speeds as you mentioned before.

I must have misunderstood, or the designer must mean something else, but I get my doubts after reading your replies carefully that it would be possible to run the 5393 at half modulator speed, and get 64x at 44K.

More info on the AKM AK5393 http://www.asahi-kasei.co.jp/akm/en/product/ak5393/ak5393.ht ml

More info on the AKM AK5392 http://www.asahi-kasei.co.jp/akm/en/product/ak5392/ak5392.ht ml

/E
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Bill Mueller:"Only very recently, has the availability of cheap consumer based gear popularized the concept of a rank amateur as an audio engineer. Unfortunately, this has also degraded the reputation of the audio engineer to the lowest level in its history. A sad thing indeed for those of us professionals."
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