Testing freerunner's audio quality

[Gennady Kupava]

Hi, list, 

Many gossips flying around about bad fr's audio subsystem quality. I
promised to proove that FR audio subsystem is good, just default
headphones quality below anything.

As today finally i overcome my lazyness and soldered 2.5mm->3.5mm jack,
and i am almost content with high sound quality of my  Sennheiser CX300
II+FR, i decided to do some basic testing.

Test environment
================
I got 2 recodings - 60 seconds of white noise and 120 seconds of piano
+voice, audacity to do spectrum analisys, cable 3,5mm<->3,5mm to connect
my old m-audio revolution 7.1 card to line-in to freerunner.

White noise
===========
1. White noise were generated by audacity original file:
http://www.bsdmn.com/openmoko/audioquality/white.wav
Spectrum:
http://www.bsdmn.com/openmoko/audioquality/whitenoise.png
2. Same noise recorded then audio-out were connected to audio-in of
sound card:
http://www.bsdmn.com/openmoko/audioquality/rec_white_directcable.wav
Spectrum:
http://www.bsdmn.com/openmoko/audioquality/whitenoise_direct.png
3. Same noise played on FR, connected to line-in of sound card:
http://www.bsdmn.com/openmoko/audioquality/rec_white_fromfrerunner.wav
Spectrum:
http://www.bsdmn.com/openmoko/audioquality/whitenoise_fr.png

Conclusion on white noise:
I see no frequency cut-offs. spectrograms look very well and close to
original file. Only exception is fall below 20Hz in fr case, but i am
unsure if any headset can reproduce such frequences very well.

Real song
=========
1. Original piece of song (piano+voice):
http://www.bsdmn.com/openmoko/audioquality/song.wav
Spectrum:
http://www.bsdmn.com/openmoko/audioquality/song.png

2. Same file played on freerunner and captured on line-in of sound card
http://www.bsdmn.com/openmoko/audioquality/rec_song_fromfr.wav
Spectrum:
http://www.bsdmn.com/openmoko/audioquality/song_fromfr.png

Conclusion on piano+voice:
I can't distingush difference in quality while replaying original file
or file recorded from freerunner. Spectrum show almost no difference.

Overall conclusion
==================
Seem audio quality completely depends on quality of headphones. You may
try to distiguish original song and song from fr youself, only do not
forget to normalize volume before attempting to do this.

regards,
Gennady.