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FS#11767 - Meier crossfeed

Attached to Project: Rockbox
Opened by Bertrik Sikken (bertrik) - Sunday, 21 November 2010, 12:33 GMT+2
Last edited by Michael Sevakis (MikeS) - Tuesday, 01 May 2012, 10:27 GMT+2
Task Type Patches
Category Music playback
Status Closed
Assigned To No-one
Player Type All players
Severity Low
Priority Normal
Reported Version Release 3.6
Due in Version Undecided
Due Date Undecided
Percent Complete 100%
Private No

Details

Attached patch adds a new crossfeed algorithm to rockbox, emulating the basic "Meier" crossfeed (2 capacitors, 3 resistors) as discussed in http://www.meier-audio.homepage.t-online.de/passivefilter.htm

This crossfeed blends a bit of low-pass filtered L signal into the R signal (and vice versa) while adding about 300 us delay to the crossfed-signal. A difference with the crossfeed already present in rockbox, is that this algorithm keeps the total spectrum flat (the one currently in rockbox accentuates low-frequency signals, making it sound a bit muffled).
This implementation is quite lightweight, just 3 multiplies per left-right pair of samples, but only has a C implementation right now (no asm).

The crossfeed effect is quite subtle and is noticeable mostly one albums that have very strong left-right separation (e.g. one instrument only on the left, another only on the right).

In the user interface, the new crossfeed option appears as "Meier" and is not configureable. The existing crossfeed is renamed to "Custom" as it allows itself to be customised.
There is no entry for the user manual yet.
   meier_v3.patch (7.3 KiB) 
 apps/plugins/mpegplayer/mpeg_settings.c |    2 -
 apps/lang/english.lang                  |   34 +++++++++++++++++
 apps/settings.h                         |    2 -
 apps/dsp.c                              |   63 +++++++++++++++++++++++++++-----
 apps/dsp.h                              |    2 -
 apps/settings_list.c                    |    6 ++-
 apps/plugin.h                           |    2 -
 7 files changed, 96 insertions(+), 15 deletions(-)

This task depends upon

Closed by  Michael Sevakis (MikeS)
Tuesday, 01 May 2012, 10:27 GMT+2
Reason for closing:  Out of Date
Additional comments about closing:  Synced to 0dd00b33 and moved to gerrit.
http://gerrit.rockbox.org/r/#/c/227/
Comment by sideral (sideral) - Sunday, 28 November 2010, 00:34 GMT+2
Nice addition. I tested this patch on a few files, and I do indeed have the impression that it accomplishes its objective (crossfeed) without requiring configuration and while maintaining a better sound quality.
Comment by Martin Sägmüller (dfkt) - Tuesday, 14 December 2010, 14:44 GMT+2
I tested this v3 patch with some "regular" and some very hard-panned music. It's really rather subtle, and IMO the v2 of this patch had more beneficial effects while still maintaining good audio clarity. Would it be possible to keep the v2 version next to this v3 one, for example selectable as "Meier 1" and "Meier 2" in the menu?
Comment by sideral (sideral) - Friday, 04 March 2011, 18:51 GMT+2
I haven't seen a v2 version of this patch anywhere. Does anyone of you still have that version lying around somewhere, and if so, could you please post it here?

In my view, the current Meier-crossfeed feature (v3 patch) is superior to Rockbox's standard crossfeed feature (better sound quality, no configuration needed) and could actually replace it. I find it hard to imagine anyone actually fiddling with the plethora of crossfeed settings we have today.
Comment by Martin Sägmüller (dfkt) - Friday, 04 March 2011, 19:58 GMT+2
V2 is the last post in  FS#11577 .

The only difference between v2 and v3 are two digits. In dsp.c replace both (0x7fffffff/NATIVE_FREQUENCY) with (0xffffffff/NATIVE_FREQUENCY).
Comment by Mark (bba1973) - Saturday, 14 May 2011, 21:57 GMT+2
Can we go ahead and get this added into the releases? I've been using it for months on my Clip+ with dfkt's build, and it's rock solid. I'd really like to get this on my 5.5G iPod too.
Comment by Johnny Chang (Eruditass) - Wednesday, 15 June 2011, 17:29 GMT+2
Does this implement the frequency dependent delay to counter the comb effect?
Comment by Bertrik Sikken (bertrik) - Wednesday, 15 June 2011, 21:02 GMT+2
Eruditass, this implementation should have no comb effect.
Comment by mysiak (mysiak) - Tuesday, 14 February 2012, 19:13 GMT+2
I fully agree that this patch is nice addition to the custom rockbox settings, would be nice including it to standard releases.

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