Rockbox Technical Forums

Support and General Use => Hardware => Topic started by: h.finn on July 22, 2010, 05:45:58 AM

Title: Hardware EQ for Ipod 5th gen.
Post by: h.finn on July 22, 2010, 05:45:58 AM
Hi everybody,
I read an old thread on the forum about a previous RB release which allowed to "equalize" the ipod hardware.
Apparently the results were excellent!
Does anybody know about it?
Is the release still available?

Many thanks,
H.
Title: Re: Hardware EQ for Ipod 5th gen.
Post by: Chronon on July 22, 2010, 05:56:15 AM
I believe the current Bass and Treble controls correspond to that.
Title: Re: Hardware EQ for Ipod 5th gen.
Post by: soap on July 22, 2010, 06:40:22 PM
When the hardware EQ was enabled as such only the low and high shelf filters actually worked.  My memory matches Chronon that the 3 band / 2 shelf interface was scrapped because of this and the two shelves renamed Bass and Treble.
Title: Re: Hardware EQ for Ipod 5th gen. & Mini
Post by: h.finn on July 23, 2010, 08:54:56 AM
Hi,

And thanks for the answer.
So I'll just use these settings and maybe tweak the cutoff.
I just have a question about something that puzzles me (I don't know if this is the right place for the topic  :-[):
I have both a 5.5 gen. video and a Mini 1st gen.
They both have RB with same settings.
The Mini sounds WAY better!!
I thought it was supposed to be the other way round :-\ :-\!!
The bass on the 5.5gen one, in particular, is extremely distorted while it's absolutely fine AND great on the Mini!

Does anybody have any suggestions?
Thanks
H.
Title: Re: Hardware EQ for Ipod 5th gen. & Mini
Post by: saratoga on July 23, 2010, 11:03:56 AM
The Mini sounds WAY better!!
I thought it was supposed to be the other way round :-\ :-\!!

They should sound the same.  If they don't, you're probably doing something wrong or one is broken.

The bass on the 5.5gen one, in particular, is extremely distorted while it's absolutely fine AND great on the Mini!

Does anybody have any suggestions?

Let me guess, you used the EQ to boost the bass?
Title: Re: Hardware EQ for Ipod 5th gen.
Post by: h.finn on July 23, 2010, 11:09:48 AM
Hi Saratoga,
Yes, i boosted the bass.......on the two ipods,
and the result i sooo different
..........
I must add that I've had the Mini since it came out and bought the video a year ago (also because I can't fit everything on the Mini anymore)
But through iTunes they sound the same
But then again.......iTunes is kind of "flat" compared to RB!
I bought the video from "reputable" sellers, I must add
Title: Re: Hardware EQ for Ipod 5th gen.
Post by: saratoga on July 23, 2010, 11:15:27 AM
Hi Saratoga,
Yes, i boosted the bass.......on the two ipods,

Don't do that, it'll distort.  The manual has some info about how to use an EQ:

http://download.rockbox.org/daily/manual/rockbox-ipodcolor/rockbox-buildch6.html#x9-1150006.8

Basically, you want to lower frequencies, not raise them, so either lower then explicitly or apply enough precut that you don't distort.
Title: Re: Hardware EQ for Ipod 5th gen.
Post by: h.finn on July 23, 2010, 11:22:09 AM
Look,
I'll experiment during the w-end (with the 5.5gen. that is, 'cause the other one's just so good).
And I undertsand your point...........still I don't understand this difference between the two!
The 5.5gen one even distorts a little (on the bass frequencies) on the equalizer preset that comes when you first install RB.
Sooo frustrating!

...............
P.S.: How do I know which one is the current eq? I mean: where do I look?
H.
Title: Re: Hardware EQ for Ipod 5th gen.
Post by: saratoga on July 23, 2010, 11:45:57 AM
The 5.5gen one even distorts a little (on the bass frequencies) on the equalizer preset that comes when you first install RB.

Post you config file from the Video.
Title: Re: Hardware EQ for Ipod 5th gen.
Post by: h.finn on July 23, 2010, 11:52:57 AM
Thanks Saratoga.
That's nice of you......I'll just do it on monday........I'm in europe and I'm finishing the day at work now............family rules say: no posting from home
 :)
so it will have to be monday 'cause ipod is not with me
Thanks again and, ............have a good w-end!!
 ;)
Title: Re: Hardware EQ for Ipod 5th gen.
Post by: h.finn on July 26, 2010, 07:57:15 AM
Ok,
Here's my setup:

Graph. Eq:
2.5   60         6.4
5.5   450       6.0
1.5   4000     2.1
2.5   15530   2.2

Bass:   +8
Treble: +12
Volume:-76dB

And the Bass is way more distorted than with the same settings on the Mini!!
I use a good quality LOD (Line Out Dock) and "class T" amp + excellent Italian loudspeakers from the early 80s.
The files are almost all uncompressed flac.

Many thanks,
H.
Title: Re: Hardware EQ for Ipod 5th gen.
Post by: torne on July 26, 2010, 08:12:38 AM
You're using the software graphic equaliser *and* the hardware tone controls? That's kind of an odd thing to be doing. You are boosting the bass twice: first Rockbox's equaliser adds 2.5dB to all the frequencies under 60Hz, then the DAC is doing it again by 8dB (not sure what shelf it uses). That's a lot of boost and doing it in two seperate ways probably doesn't help. Also, your Q value for the bass shelf is 6.4 - the manual explicitly says that you should leave it as 0.7 for the shelf filters. You're doing the same for the treble, of course...

-76dB volume is incredibly quiet. You mention you are using line out, which means that the entire top range of the volume adjustment will do nothing, since line out is line level by definition; however, Rockbox supports a wider range of volume adjustment than the DAC does, and we simulate the extra range by digital processing of the audio to reduce the volume before passing it ot the DAC. If you have it turned down to -76 in order to reach this, then this means you are introducing a *third* set of audio processing. You shouldn't use the volume control this way; leave it on a normal setting and control the volume externally if you are using line out.

The DACs and analogue hardware are not identical between the different models, so while yes, normally people expect the Video to sound better, your settings are highly abnormal and it's hard to say what to expect ;)
Title: Re: Hardware EQ for Ipod 5th gen.
Post by: h.finn on July 26, 2010, 08:23:04 AM
Hi Torne,
I appreciate your precious suggestions!
So: I should use either the graphical eq or the hardware, right?
If I go for the former: any suggestion about a good bass boost? ;)

I put the volume at -76dB (and obviously increase the volume on my amp) to avoid any distortion.
That's the only effective way I found to do it.

I don't understand:
 "You mention you are using line out, which means that the entire top range of the volume adjustment will do nothing, since line out is line level by definition; however, Rockbox supports a wider range of volume adjustment than the DAC does, and we simulate the extra range by digital processing of the audio to reduce the volume before passing it ot the DAC"

Thanks again,
H.
Title: Re: Hardware EQ for Ipod 5th gen.
Post by: torne on July 26, 2010, 09:39:17 AM
Line out is line level, 0dB, i.e. it's not affected by volume changes. This is normal and should not cause distortion.

Turning the volume down *very* far, as you are doing, switches Rockbox to a mode where it actually reduces the volume of the digital audio in the DSP stage; this is not something you should have to be using to avoid distortion.

Read the manual for suggestions as to how to configure the graphical equaliser; it's a matter of taste, but as saratoga pointed out, you generally want to either *lower* certain frequencies, or set the precut (overall volume reduction) to be at least as big as the highest boost amount, to avoid distortion and clipping.

The hardware tone controls (the bass/treble settings) automatically precut the volume as needed, but I'm not sure if this precut actually works on line-out. If you can get the audio effect you want using only those, then it's more efficient to leave the equaliser disabled, since the tone controls are "free" whereas the EQ uses CPU time.
Title: Re: Hardware EQ for Ipod 5th gen.
Post by: h.finn on July 26, 2010, 09:49:10 AM
Allright,
.........so basically you suggest I stick to the bass/treble settings (by the way, the bass precut works through the LOD dock) and leave the graphical  eq "untouched" (i.e. the way it is when first installing RB)?

Thanks
P.S.: could you tell me how to know the "current" eq settings, the ones using at any given time?
P.P.S.: just found this:
http://www.rockbox.org/tracker/10768
"Details
I'm reporting a bug which we tracked down in the german rockbox forum.
Rockbox plays a loud distortion (without music) if you have bass and equalizer both turned on. Any bass setting above 0 shows this behavior.
Tested with a current build after reseting the settings. (r23566-091108)

steps to reproduce:
01. download current build
02. reset settings
03. apply bass
(no distortion this far when resuming playback via menu)
04. apply EQ, > distortion when resuming playback after stop
05. turn off bass > no distortion"
Title: Re: Hardware EQ for Ipod 5th gen.
Post by: torne on July 26, 2010, 11:22:55 AM
I suggest you use whichever settings make the audio sound pleasing to your ear; that's what they're for. I told you which was more efficient, but that's not a suggestion :)

The bug you linked there sounds like perhaps the tone controls and equaliser interfere when it's deciding whether to precut the audio and by how much...
Title: Re: Hardware EQ for Ipod 5th gen.
Post by: h.finn on July 26, 2010, 11:31:05 AM
ok
I'll experiment
 :)
Title: Re: Hardware EQ for Ipod 5th gen.
Post by: saratoga on July 26, 2010, 02:19:27 PM
Ok,
Here's my setup:

Graph. Eq:
2.5   60         6.4
5.5   450       6.0
1.5   4000     2.1
2.5   15530   2.2

Bass:   +8
Treble: +12
Volume:-76dB


The bass preset also includes a precut to avoid distortion.  Did you remove the precut? 
Title: Re: Hardware EQ for Ipod 5th gen.
Post by: h.finn on July 27, 2010, 05:18:24 AM
" Did you remove the precut?"
You mean the cutoff?
The cutoff is at 1
Title: Re: Hardware EQ for Ipod 5th gen.
Post by: Chronon on July 27, 2010, 06:58:44 PM
Settings > Sound Settings > Equalizer > Precut

It only takes non-positive gain settings (mine is -3.0 dB, for example).
Title: Re: Hardware EQ for Ipod 5th gen.
Post by: soap on July 27, 2010, 07:05:30 PM
Are you using pre-cut equal to the amount of software EQ being applied?
Title: Re: Hardware EQ for Ipod 5th gen.
Post by: h.finn on July 28, 2010, 03:23:31 AM
OOOOOOOOPPPPPPPPPSS
Sorry, I didn't understand
 :-[ :-[
I actually have precut at 0
!!
Could that be part of the problem?
Because yesterday evening I switched off the equalizer all together and moved the bass to 0 value and (the bass) was still distorted.
...
P.S. i noticed that on the RB instructions, when the graphical eq is shown, there is always, at bottom of the screen, the text: "Edit mode: Gain".
As in:
http://download.rockbox.org/daily/manual/rockbox-iriverh300/configure_rockbox/images/ss-equalizer-220x176x16.png
..........
Well: I actually don't have that little footnote!
??
Title: Re: Hardware EQ for Ipod 5th gen.
Post by: soap on July 28, 2010, 06:38:54 AM
If you don't apply precut any software EQ gain is likely to exceed the headroom in your audio files and clip (distort.)

Modern mastering techniques leave almost no headroom, and older-style mastering techniques never, in my experience, left the (at least) 12 dB of headroom you need to prevent your EQ settings from clipping.


*I said (at least) because I didn't study the Q values of your software EQ settings and for all I know your bands are overlapping, meaning that some frequencies may be boosted more that the highest gain value (12 dB) I saw.

So, in summary.

1 - negative pre gain in the software EQ equal to the maximum applied EQ gain.
2 - "Sane" volume level set to prevent Rockbox from applying any volume control in the digital domain.
3 - Line-out or volume set to 0 and then use headphone out as a line-out.
4 - Distortion still?
 
Title: Re: Hardware EQ for Ipod 5th gen.
Post by: h.finn on July 28, 2010, 06:42:12 AM
Hi Soap,
I'm taking notice of your suggestions.
And will try them out tonight!
But: "use headphone out as a line-out"
??
The sound quality is inferior to the dock!
Isn't it?

H.
Title: Re: Hardware EQ for Ipod 5th gen.
Post by: torne on July 28, 2010, 07:07:47 AM
Why should it be? Line out and headphone out are the same thing, except the latter has a volume control on it. They're both driven by the same DAC. If you set the volume to 0dB then headphone out will be at the exact same level as line out.
Title: Re: Hardware EQ for Ipod 5th gen.
Post by: h.finn on July 28, 2010, 08:53:40 AM
Rrrightt!
That's a kind of revelation to me
 ::) ::)
'cause I thought that the audio going through the headphone output undergoes an additional step of amplification, potentially coloring the sound or adding noise.
I read somewhere:
"The line out is a line level signal, meaning it doesn't go through the iPods headphone amp circuitry.
If you are going to another source you will get better results with the line level"
????
Also I found this NOT to be true:
"...you basically have control over the volume of a headphone plug, but a line out is at a constant volume" : well, how come I can change the volume in line out?
Title: Re: Hardware EQ for Ipod 5th gen.
Post by: torne on July 28, 2010, 09:12:57 AM
If you don't know what precut is then you probably shouldn't be worrying about the impact of an amplifier on the sound.. ;)

soap suggested you use line out, or headphone output at 0dB; you are already using line out, so that's fine. The difference between the two is not something you will notice.

I already explained to you what Rockbox does with the volume control: in order to support playing audio very quietly (quieter than the lowest setting the hardware supports, but not actually muted) Rockbox scales the digital audio's amplitude down in software if you decrease the volume extremely far. Since this is done in the digital domain it also affects line out, but if you were using the headphone output you would find the volume at those levels is already so quiet as to be basically inaudible ;)
Title: Re: Hardware EQ for Ipod 5th gen.
Post by: h.finn on July 28, 2010, 09:28:02 AM
ok
point taken
 ;)
 :'(
I'll study all the info a bit
 :)

H.
P.S.: just a little point: having a "good ear" for music, doesn't necessarily mean knowing the technical details, right?
 ;)
H.
Title: Re: Hardware EQ for Ipod 5th gen.
Post by: torne on July 28, 2010, 10:45:54 AM
No, but the sound quality differences between minor variations in the analogue path, on a portable MP3 player, are something that generally only "audiophiles" would care about; they're not something that people actually *hear* unless the hardware is crappy. There's a difference between having a good ear for sound and being concerned about entirely hypothetical differences ;)