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Subject: speed adjustment on Archos models, myth and facts

speed adjustment on Archos models, myth and facts

From: [IDC]Dragon <idc-dragon_at_gmx.de>
Date: 2005-12-06

There's been some traffic about it, including some not precisely correct
answers I'd like to comment.

First, on Archos models we can (and do) change the pitch by clocking the
hardware decoder different. The effect is like playing a tape with a
different feed, affecting both pitch and speed. As Jens said, not accessible
on Ondio for a lack of buttons.
This pitch setting is not persistent, if you power cycle the box it's back
to 100%

About changing speed without pitch:

Jens wrote:
> Preserving the pitch while changing speed would only be possible
> if someone modifies the MP3 decoder, i.e. code for the MAS. Next
> to impossible unless you are working with Micronas...

Bluechip wrote:
> Close to impossible on the Archos units - should be within reach on the
> more poweful units.

No, it *is* possible. The ancestor of the Archos line, the Oscar, can do the
trick. With the same old SH CPU, it can jog-shuttle the playback over a wide
range, forward and backwards, including playing on the spot. The result is
said to be quite satisfying.

Technically, we'd need an mp3 "framewalker" during playback and do the
bitswap afterwards, as a final output step. Non-100% playback is done by
skipping or repeating mp3 frames while obeying the bit reservoir, chopping
it off or inserting extra frames for it if necessary. We'll get audible
FF/FR for free as a part of this.

If you for whatever reason want to change the pitch and preserve the speed,
withing certain limits we could do the above trick and use the decoder clock
to drag it back to 100% speed.

I'd like to do a renovation of the record/playback code with Jens next year,
once real life lets me loose again. :-)

Jörg

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Received on Tue Dec 6 11:28:33 2005

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