Hi,
In the equalizer.c and filter.c source for madplay, it seems to define no equalisation (flat) as MAD_F_ONE, but I couldn't find any documentation on what the upper and lower limits on this were, and whether this should be a linear scale.
Also in attenuate_filter what is the maximum scalefactor?
Any help appreciated, docs seem to be a bit mute on the subject. :/
Yours Unwhettedly, Robert John Shepherd.
Editor DVD REVIEWER The UK's BIGGEST Online DVD Magazine http://www.dvd.reviewer.co.uk
For a copy of my Public PGP key, email: pgp@robertsworld.org.uk
On Feb 18, 2004, at 1:20 AM, Robert John Shepherd wrote:
In the equalizer.c and filter.c source for madplay, it seems to define no equalisation (flat) as MAD_F_ONE, but I couldn't find any documentation on what the upper and lower limits on this were, and whether this should be a linear scale.
Also in attenuate_filter what is the maximum scalefactor?
The lower limit is 0, reducing the signal to absolute silence. The upper limit depends on the signal being modified, but cannot be greater than MAD_F_MAX. The risk of course is you may amplify the signal beyond the range of full scale (causing clipping), or worse, beyond the range of representable values.
Usually it is best to calculate a scalefactor from the desired change in decibels. For example, to reduce the signal by 3 dB, calculate:
scalefactor = mad_f_tofixed(pow(10, -3.0 / 20));
Using the decibel scale, the effective range is limited from DB_MIN (-175) to DB_MAX (+18).
Not hearing the results from playing with this that I expected, so I'm guessing something isn't quite right with the formula you provided. :/
If I use that I get very odd results, not at all like I expect, yet if I use something like MAD_F_MAX / 4 then things do sound somewhat more how I'd expect them to.
Very confused. :/
Also is there a list of what subbands apply to what frequencies anywhere? I've not had any luck in the usual places, every site and its dog lists the rough process of how mp3 is encoded/decoded but no specifics. :/
Yours Unwhettedly, Robert John Shepherd.
Editor DVD REVIEWER The UK's BIGGEST Online DVD Magazine http://www.dvd.reviewer.co.uk
For a copy of my Public PGP key, email: pgp@robertsworld.org.uk
-----Original Message----- From: mad-dev-admin@lists.mars.org [mailto:mad-dev-admin@lists.mars.org] On Behalf Of Rob Leslie Sent: 18 February 2004 20:03 To: mad-dev@lists.mars.org Subject: Re: [mad-dev] Suggested limits for madplay equalizer_filter and attenuate_filter functions
On Feb 18, 2004, at 1:20 AM, Robert John Shepherd wrote:
In the equalizer.c and filter.c source for madplay, it
seems to define
no equalisation (flat) as MAD_F_ONE, but I couldn't find any documentation on what the upper and lower limits on this were, and whether this should be a linear scale.
Also in attenuate_filter what is the maximum scalefactor?
The lower limit is 0, reducing the signal to absolute silence. The upper limit depends on the signal being modified, but cannot be greater than MAD_F_MAX. The risk of course is you may amplify the signal beyond the range of full scale (causing clipping), or worse, beyond the range of representable values.
Usually it is best to calculate a scalefactor from the desired change in decibels. For example, to reduce the signal by 3 dB, calculate:
scalefactor = mad_f_tofixed(pow(10, -3.0 / 20));Using the decibel scale, the effective range is limited from DB_MIN (-175) to DB_MAX (+18).
-- Rob Leslie rob@mars.org
On Feb 19, 2004, at 4:40 PM, Robet John Shepherd wrote:
Not hearing the results from playing with this that I expected, so I'm guessing something isn't quite right with the formula you provided. :/
If I use that I get very odd results, not at all like I expect, yet if I use something like MAD_F_MAX / 4 then things do sound somewhat more how I'd expect them to.
I guess it would help to understand what you're trying to accomplish and what sound you were expecting to hear. :-)
Also is there a list of what subbands apply to what frequencies anywhere?
This message may be of some help:
http://www.mars.org/mailman/public/mad-dev/2003-July/000869.html
Cheers,
Also is there a list of what subbands apply to what frequencies anywhere?
This message may be of some help: http://www.mars.org/mailman/public/mad-dev/2003-July/000869.html
Ah that explains a lot, and frustratingly offers an easy way of boosting frequencies from the midrange upwards but very little control below. :/
I guess I need to look elsewhere for some source which will enable me to impliment a 10 band graphic equaliser. Arsicles! :)
Still, at least I can increase the gain on the output now if need be, so all isn't lost...
Thanks Rob!
Yours Unwhettedly, Robert John Shepherd.
Editor DVD REVIEWER The UK's BIGGEST Online DVD Magazine http://www.dvd.reviewer.co.uk
For a copy of my Public PGP key, email: pgp@robertsworld.org.uk
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Rob Leslie -
Robert John Shepherd -
Robet John Shepherd