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-   -   strange frequency response of m2tech evo (http://www.diyaudio.com/forums/pc-based/203665-strange-frequency-response-m2tech-evo.html)

elviukai 2nd January 2012 09:34 PM

strange frequency response of m2tech evo
 
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strange frequency response of m2tech evo

anyone has done any measurements of m2tech evo usb/spdif converter? I am somewhat confused with it objective performance numbers(I am quite satisfacted with it sonic , even if quite diferent form other product)

when first tried m2tech evo sonicaly I noticed some lack of airiness in sound(less expansive soundstage) but the soundstage focus was superb as bass tightness. one day I decided to use m2tech evo for speaker measurements(it gets digital MLS signal from laptop, and feed DAC) to my surpsise i saw some top octave roll off. on white nois eI can even tell from the ears(I have designing speakers form many years) i imedialty returned to chineese made thera-linx usb/spdif converter (which measures EXACTLY like internal pc measuring equipment),
thinking my unit is defective i ordered another m2tech evo unit with more late serial number, hoping its a problem of actual unit rather then design fault. but it measured the same. later i acquired weiss int202 which also confirmd to be flat ( weiss int 202 measured exactly the same as thera-linx or internal pc measuring hardware)

i tried everything -
1)diferent DAC's,
2)rca. xlr, st outputs(didnt tried i2s as its format not compatibile with my dac's)
3) variuos power suplies- the problem stays here.

could m2tech evo designer answer here. I do not want to shock customers, but I want an answer why this interface have rolled off top octave. it evenmeasures from 1.5meter on speaker axis!!

greetings to all
R.

phofman 3rd January 2012 11:49 AM

It is just a usb-spdif converter, with no resampling, IIRC. How could it roll off the frequency response of your chain? Jitter raises noise floor, but how could it attenuate higher frequencies?

erin 6th January 2012 07:08 AM

I think that is what he is trying to figure out. The Teralink X works fine, and two EVO's roll off the highs. I'd like to know the answer too.

phofman 6th January 2012 07:48 AM

Edited

phofman 6th January 2012 07:58 AM

Actually, my guess is the two tested spdif transmitters differ in pre-emphasis bit in SPDIF preamble and the DAC respects this information. That would produce this behaviour.

Status of the pre-emphasis bit in SPDIF stream can be checked with any card with SPDIF input e.g. in linux, perhaps there is a way in other OSes too.

elviukai 6th January 2012 07:58 AM

I thought same thing, but I tried -
diferent EVO, diferent PC, diferent dac, diferen input, even diferent cables. how it comes that all other devices measures identical except EVO? I would say its not a coincidence..

phofman 6th January 2012 08:06 AM

If you have a DAC with pre/de-emphasis indicator (no idea if any exists :-) ), you can check.

elviukai 6th January 2012 08:14 AM

Quote:

Originally Posted by phofman (Post 2849012)
If you have a DAC with pre/de-emphasis indicator (no idea if any exists :-) ), you can check.



yes they have. well at least one i have tried.- here excerpt from manual-

De-Emphasis LED
Some digital recordings are encoded with pre-emphasis contouring. Your DAC automatically
recognizes and processes them. An LED will indicate that the recording is being de-emphasized.

no lights will come. now I need to open the dac and valid that deempahasis led is working? :)

seriuosly , I got one sugestion to isntall m2tech young dac drivers instead original evo. I will try this..

phofman 6th January 2012 08:24 AM

Quote:

Originally Posted by elviukai (Post 2849018)
no lights will come. now I need to open the dac and valid that deempahasis led is working? :)

I do not know, even that may be the case :-)

Quote:

Originally Posted by elviukai (Post 2849018)
seriuosly , I got one sugestion to isntall m2tech young dac drivers instead original evo. I will try this..

I do not see how drivers could change frequency characteristics of bit-perfect digital transmission, and consistently too. Provided the transmission is really bit-perfect which should be verified first.

woodturner-fran 6th January 2012 09:02 PM

It might not be obvious why different drivers would affect the measurements but I wouldn't be a bit surprised. I certainly hear a difference using hiface and young drivers.....


Fran


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