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Measuring Amp frequency response with free software!

post #1 of 25
Thread Starter 

Check out my post here:

 

http://www.head-fi.org/t/643225/measuring-amp-frequency-response-with-free-software

post #2 of 25

It is interesting to see in the first graph that amps globally sound the same, the difference is so small it's not audible.

post #3 of 25
Quote:
Originally Posted by Puranti View Post

It is interesting to see in the first graph that amps globally sound the same, the difference is so small it's not audible.

 

This is just frequency response, unloaded.  No distortion measurements, and who knows what changes (well, mostly distortion) when a nontrivial amount of current is drawn, what the power limits are.  No noise measurement, no assessment of channel balance, stability, and many other factors.  It's still a big leap to get to "sound the same".

 

But it's definitely better than nothing, and I'd be interested in results for a lot of tube amps and more exotic designs, see how much some are rolling off treble.  Or what some amps' bass boosts or other tone controls do.  You'd think that this kind of basic info would be more available.

post #4 of 25
Quote:
Originally Posted by Puranti View Post

It is interesting to see in the first graph that amps globally sound the same, the difference is so small it's not audible.

 

The bass roll-off on the cyan trace would be audible in an ABX test.

 

By the way, there is also an older thread about PC based measurements here.

post #5 of 25
Thread Starter 
Quote:
Originally Posted by mikeaj View Post

 

This is just frequency response, unloaded.  No distortion measurements, and who knows what changes (well, mostly distortion) when a nontrivial amount of current is drawn, what the power limits are.  No noise measurement, no assessment of channel balance, stability, and many other factors.  It's still a big leap to get to "sound the same".

 

But it's definitely better than nothing, and I'd be interested in results for a lot of tube amps and more exotic designs, see how much some are rolling off treble.  Or what some amps' bass boosts or other tone controls do.  You'd think that this kind of basic info would be more available.

Agree, it's not too much but pretty cool for stuff I already have available. It's not great for measuring absolute quality, but good for comparing relatives. For example with my HE-500 I got more bass on my O2 than my BitHead (despite BitHead driving loud enough for me w/o clipping) and this clearly shows the audible difference I saw.

post #6 of 25
Thread Starter 
Quote:
Originally Posted by stv014 View Post

 

The bass roll-off on the cyan trace would be audible in an ABX test.

 

By the way, there is also an older thread about PC based measurements here.

 

Yea, I noticed the BitHead had less bass way down there compared to my O2 even before doing these measurements. It was very distinct (100% sure I can reliably pinpoint in ABX test). Same with the headphone processor EQ change..

post #7 of 25
Quote:
Originally Posted by stv014 View Post

 

The bass roll-off on the cyan trace would be audible in an ABX test.

 

By the way, there is also an older thread about PC based measurements here.

 

Thought the same about this cyan trace.

post #8 of 25

Just measured my Asgard/Titanium HD, completely neutral. So neutral that I had to try a few different measurement types to confirm because I thought I did something wrong.

post #9 of 25
Thread Starter 
Quote:
Originally Posted by chewy4 View Post

Just measured my Asgard/Titanium HD, completely neutral. So neutral that I had to try a few different measurement types to confirm because I thought I did something wrong.

Post the image?
post #10 of 25
Quote:
Originally Posted by moshen View Post


Post the image?

Asgard to Titanium HD line in (using monoprice Y cable):

HD Line out to line in:

 

These are both just the measurements I get when calibrating. When using the HD to HD as calibration for the Asgard I get a completely flat line, even throughout the sub-bass. 


Edited by chewy4 - 12/28/12 at 3:50pm
post #11 of 25

So, the Asgard itself then has a fairly flat response, but the sound card loopback is not that good (are the playback and recording both at 44.1 kHz sample rate ?).

 

Edit: the slight bass roll-off is normal for the Titanium HD, but the high frequency ripple and roll-off could be the result of a software problem.


Edited by stv014 - 12/29/12 at 4:24am
post #12 of 25
Quote:
Originally Posted by stv014 View Post

So, the Asgard itself then has a fairly flat response, but the sound card loopback is not that good (are the playback and recording both at 44.1 kHz sample rate ?).

 

Edit: the slight bass roll-off is normal for the Titanium HD, but the high frequency ripple and roll-off could be the result of a software problem.

Yeah the bass rolloff is completely normal for the HD, goes completely inline with the measurements given by the manufacturer. Treble isn't actually rolled off, at 20Hz it's right about at the reference line(the sweep was from 0-20,100) which is actually a bit higher than creative's specs(-.25dB rolloff). The ripple isn't normal though and is probably caused by something else yeah, phase is jumping up and down at that point, I don't really know the significance of phase though. Both are at 44.1kHz.

post #13 of 25

Maybe I missed something, but the graphs seem to show more than 3 dB attenuation at 20 kHz.

post #14 of 25

Er yeah, I think you're right there. I was thinking that line was 30kHz...

 

That definitely shouldn't be that severe.

post #15 of 25

It could be a problem in the measurement software, or unwanted (low quality) sample rate conversion by Windows drivers.


Edited by stv014 - 12/29/12 at 8:44am
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