strange frequency response of m2tech evo

[elviukai]

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]

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]

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]

Edited

[phofman]

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]

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]

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

[elviukai]

Originally Posted by phofman

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]

Originally Posted by elviukai

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 :-)

Originally Posted by elviukai

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]

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