Testing freerunner's audio quality

[Gennady Kupava]

В Чтв, 23/09/2010 в 06:47 +0200, Dr. H. Nikolaus Schaller пишет:
> Hi,
> the problem is the bass. Initially, It was difficult to hear differences
> by playing two sounds one after the other. So until you have listened
> music on a bass fixed Freerunner, you would say it is quite ok.
> 
> I was only able to hear the difference after taking one original Freerunner
> and one with Bass-Fix applied. After a while you get that there *is* a
> difference in low frequencies.
> 
> What I have done is this test: create a sinus sweeping from 10 to 100 hz.
> Without bass fix you can't hear it before it comes to the 50 hz range.
> 
> sox -n -t wav - synth 10 sine 10-100 >file.wav
> 
> This can be seen on scope outputs as shown here:
> 
> http://freeyourphone.de/portal_v1/viewtopic.php?f=20&t=1723&p=17279&hilit=bass+fix#p17251
> 
> Can you please compare you device?
> 
> One effect may also be the input impedance of your line card. Did you connect
> it in parallel to a headset?
> 
> BR,
> Nikolaus
> 

Yeah, big sorry - my freerunner has bass-fix made by Paul (many many
thanks to Paul). I wanted but seem just forgot to mention it in my
letter, as it took much longer than i expected and i had to finish it a
bit in hurry.

Re-thinking about it today, i found also few other flaws - white noise
is actually 10 seconds and white noice spectrum is really about little
bit different time interval for each sample. I had to cut white noise
samples to right offset and right lenght to compare them in right way.
But main test is perfectly correct - song output is of high quality.

But anyway, about your oscillograms (google translate is nice thing!) -
it seems that in unfixed case, you have 2 times voltage diff between
40hz and 100hz, this means 3dB. Yes, this will affect sound below 100Hz,
but this influence will be less than effect from earpieces. 

Btw, Wolfson has bass controls. interesting is it possible to compensate
bass-problem with it. Or is it possible to get frequency response and
feed to some alsa-plugin equaliser to correct it.

Common earpieces frequency response:
http://www.thg.ru/video/cheap_headphones_2007/images/sennheiser_cx300_1.png

You can see that it should influence sound quality much more than FR
audio subsystem.

Gennady.