what is wrong?

[HNaga 10+ year member]

s playing with THD Anayzer, I tested my Creative XMod sound card

I made a loop between IN and OUT and THD analyzer worked fine

I tried to do the same with my amp , connected XMod OUT to Amp IN and Amp OUT to XMod IN.

Though THD Analyzer produce Fixed freq tune , Distortion was variable

from 95% to 20 %

every arameters was fixed Volume , freq and DB.

what is wrong??

Click to read more...

 

[JimJ 5,000+ posts]

Does your sound card have a speaker-level input? Sounds like you're trying to run speaker-level outputs into a line-level input...

 

[HNaga 10+ year member]

The sound card is creative Xmod , it has speakers, mic and line_in

I connected Speakers into amp IN and line in into Amp Aux out.

 

[HNaga 10+ year member]

As mentioned in DSSF manual

THD analyzer measures the Total Harmonic Distortion of the system. THD is a measure to evaluate the linearity of the system,

and it is defined as the ratio of the geometric mean of the harmonic components (v1, v2, v3, v4, v5, ... v30) and the

fundamental component (v1) when the sinusoidal wave is inputted to the system. Usually it is expressed in dB or %.

In the THD analyzer, three different measurements are available: a) manual measurement, in which the distortion is

measured for the specific frequency and the output level, b) frequency sweep measurement, in which the measurement

frequency is changed automatically, and c) level sweep measurement, in which the output level is changed automatically.

THD analyzer can measure the distortion of the amplifier very effectively. For example, connect the soundcard's output to the

amplifier, and connect the amplifier's output to the soundcard's input. You don't need to connect the soundcard's output and

input directly. THD analyzer compares the input and the output signals automatically and gives the result (distortion).

Measurement result can be saved as a screen picture. MMLIB can be used to manage the image file.