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Subject: RE: Sound quality test
From: Fred Maxwell (rockbox_at_anti-spam.org)
Date: 2004-03-23

Gajdos_at_metatem.net wrote:

> If the original firmware mixes the channels in "stereo mode", and someone
> really wants to mimic their error in that case, then why not an "archos
> stereo" setting, but please leave the "stereo" setting pure.

While I agree that Rockbox should output a true stereo signal by default,
crossfeeding for headphone use is not an "error." It is a very desirable
feature found on very expensive, high-end headphone amps. Those headphone
amps are among the best money can buy -- if you have the money to spend
thousands of dollars (U.S.) on a headphone amp.

To those who write off crossfeeding as an "error" or as a form of
distortion, I will point you to this page by Meier Audio:

http://home.t-online.de/home/meier-audio/crossfeed.htm

>From that page:

"Firstly, the sound of a source to the right side of the listener (e.g. the
right loudspeaker) not only reaches the right ear but, attenuated and
delayed, is also heard by the left ear. The level of attenuation and the
delay time of this crossfeed signal provide important directional
information.

Secondly, the soundwaves are partly absorbed and partly reflected by the
tissues of the head. Reflections at the oracles (pinnae) interfere with the
soundwaves that directly enter the ear-channel and amplify or attenuate
specific frequency components. Since these reflections depend on the
direction of the soundwave the "color" of the sound changes with the
direction of the source.

Thirdly, reflections of the soundwaves from the walls, ceiling and floor of
our listening room produce reverberation that conveys an extra feeling of
space."

Rockbox developers should be working on developing an advanced crossfeeding
option that includes delays, frequency shaping to mimic the effect of the
pinnae of the ears, and reverberation to simulate the effects of a listening
room -- not writing it off as something deserving of scorn.

Jörg mentioned in another post which I received while composing this, the
Headwize web site. That site has a tremendous amount of information on the
psychoacoustics of headphone listening and state of the art headphones and
headphone amps. Here's a link to the main page:

http://www.headwize.com/

Regards,
  Fred Maxwell

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