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#231935 - 24/10/2004 18:50 Re: Experiences with Auto EQ [Re: genixia]
SE_Sport_Driver
carpal tunnel

Registered: 05/01/2001
Posts: 4903
Loc: Detroit, MI USA
Quote:
Q is defined as Fc/Fh-Fl. Fh and Fl are defined as -3dB points. As soon as you boost beyone +3dB you're boosting outside of that range.


I know you didn't come up with this definition of parametric EQ, but this image seems to support the view that increasing gain does not increase the range of frequencies being amplified.



Image is from here .
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Brad B.

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#231936 - 24/10/2004 18:53 Re: Experiences with Auto EQ [Re: SE_Sport_Driver]
wfaulk
carpal tunnel

Registered: 25/12/2000
Posts: 16706
Loc: Raleigh, NC US
That device also doesn't seem to have a Q adjustment, so they may have just elided that sort of info.
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Bitt Faulk

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#231937 - 24/10/2004 21:19 Re: Experiences with Auto EQ [Re: wfaulk]
wfaulk
carpal tunnel

Registered: 25/12/2000
Posts: 16706
Loc: Raleigh, NC US
FWIW, Wikipedia defines Q. It supports the 3dB thing and specifically calls out another bandwidth theory about it as incorrect.
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#231938 - 24/10/2004 21:53 Re: Experiences with Auto EQ [Re: wfaulk]
SE_Sport_Driver
carpal tunnel

Registered: 05/01/2001
Posts: 4903
Loc: Detroit, MI USA
Well, the evidence is stacking up against the cute Flash animation I saw that was probably designed by some graphics dude who doesn't even own a car, muchless a car stereo.

Assuming that's the case... where do we go from here? If applying large negative or possitive gains on any band will result in those bands overlapping, we should try to apply moderate gain (both possitive and negative) centering around the 0dB point. Yet, this inevidably causes us to apply possitive gain to our EQ which in turn, can result in clipping of the digital signal. What are we to do?

The only solution I can think of from the top of my head is to set your input gain (on the amp) with your Volume set to -10dB. Then, any adjustments made to the EQ, even if you add upto 10dB to any band, will not clip the signal before it is sent to the proc-amp. Am I getting this right?

That solution seems like it "would work" but we won't be getting the best signal to noise ratio (yet I doubt we'd notice). My main problem with it is that we'd have to remember that -10dB would be the highest we could set the volume without clipping. That's just ugly. Yet, if the input gain was properly set, I suppose we'd never have to raise the volume past -10dB without the music being too loud anyway...
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#231939 - 24/10/2004 22:13 Re: Experiences with Auto EQ [Re: SE_Sport_Driver]
wfaulk
carpal tunnel

Registered: 25/12/2000
Posts: 16706
Loc: Raleigh, NC US
Someone should design an app where you can plug in your measured results and have it graph them and then either provide you with an EQ where you could see the results as you twiddle with them or have it suggest settings. Of course, this is more graphics programming, more analog signal understanding, and more mathematics knowledge than I have.
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#231940 - 24/10/2004 22:42 Re: Experiences with Auto EQ [Re: wfaulk]
SE_Sport_Driver
carpal tunnel

Registered: 05/01/2001
Posts: 4903
Loc: Detroit, MI USA
Agreed. We might be getting worked up about nothing here. Depending on the Q setting, these other frequencies might not even be effected. Maybe running the 1/3 octave tests a few times would show if there were any peaks generated by excessive +/- gain.

We still haven't decided on which 8 frequencies to use if we want to use Treble/Bass adjustments. Could we use the EQ tutorial to get a "flat" response then bump up bands 2 and 9 for Bass/Treble? It's sad we can't access the DSP's built in Treble/Bass.
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#231941 - 25/10/2004 01:32 Re: Experiences with Auto EQ [Re: wfaulk]
SE_Sport_Driver
carpal tunnel

Registered: 05/01/2001
Posts: 4903
Loc: Detroit, MI USA
I finally found that link... JL Audio
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#231942 - 25/10/2004 07:02 Re: Experiences with Auto EQ [Re: SE_Sport_Driver]
mtempsch
pooh-bah

Registered: 02/06/2000
Posts: 1996
Loc: Gothenburg, Sweden
And looking at the text regarding Q, they're contradicting what's shown in the graph and agreeing with what's been said here:

Quote:
"As the level of boost increases, you are not just boosting frequencies within the defined bandwidth. There will still be considerate boost outside the defined bandwidth, especially with lower "Q" settings."


But then they also add a sentence that says that the Q value doesn't remain constant while you fiddle with the boost knob on their amps - so the graph still makes sense for their implementation of the circuitry:

Quote:
"Please note that the "Q" setting marked on the amplifier is referenced to maximum boost. "Q" will drop in value as boost" [text is cut off there, I assume it should say "level is decreased." or something similar]
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#231943 - 25/10/2004 09:54 Re: Experiences with Auto EQ [Re: mtempsch]
SE_Sport_Driver
carpal tunnel

Registered: 05/01/2001
Posts: 4903
Loc: Detroit, MI USA
Ah... now that's making sense..
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#231944 - 25/10/2004 10:46 Re: Experiences with Auto EQ [Re: wfaulk]
peter
carpal tunnel

Registered: 13/07/2000
Posts: 4148
Loc: Cambridge, England
Quote:
FWIW, Wikipedia defines Q

Note that the "cutoff frequency" definition linked from there has a typo: -3dB is 10^-0.3 or 50.1%, not 70.1%.

IANAJ(*) but as I understand it, the "-3dB" refers to 50.1% of the size of the effect at the centre frequency, not 50.1% of the output response. So if your gain on a particular EQ channel is +2dB of the output response, the "-3dB points" of that channel are where the effect on the output response is 50.1%, or half that: in other words, the frequencies where the effect on the output response is +1dB.

This means that any adjustment has some effect beyond the -3dB points. Indeed, any adjustment theoretically affects the entire audio spectrum, though the effects become negligible at any great frequency distance from the centre. Quite how rapidly they fall off (for instance, where the -6dB points are) depends on the exact shape of the filter.

As a concrete example, if you have an EQ band centred on 100Hz, with gain of 4dB and Q of two octaves, the boost would be +4dB at 100Hz, +2dB at 50Hz, and also +2dB at 200Hz. Frequencies just below 50Hz would be boosted by just less than 2dB, as would frequencies just above 200Hz.

Interpreting the "-3dB points" to mean "the places where 3db less difference is made to the output response" would make Q meaningless for EQ bands whose centre gain was smaller than 3dB.

Peter

(*) I Am Not A John, or, put differently, I'm not one of Empeg's two EQ gurus.

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#231945 - 25/10/2004 12:09 Re: Experiences with Auto EQ [Re: peter]
wfaulk
carpal tunnel

Registered: 25/12/2000
Posts: 16706
Loc: Raleigh, NC US
Quote:
Note that the "cutoff frequency" definition linked from there has a typo

So fix it!
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#231946 - 25/10/2004 12:22 Re: Experiences with Auto EQ [Re: wfaulk]
peter
carpal tunnel

Registered: 13/07/2000
Posts: 4148
Loc: Cambridge, England
Quote:
So fix it!

Oh, is that how it works? Right-ho then.

Peter

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#231947 - 25/10/2004 12:32 Re: Experiences with Auto EQ [Re: wfaulk]
genixia
Carpal Tunnel

Registered: 08/02/2002
Posts: 3411
Yeah, fix it so that it says the correct 70.7% please.
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#231948 - 25/10/2004 12:37 Re: Experiences with Auto EQ [Re: genixia]
peter
carpal tunnel

Registered: 13/07/2000
Posts: 4148
Loc: Cambridge, England
Quote:
Yeah, fix it so that it says the correct 70.7% please.

10dB corresponds to multiplying by 10. So -10dB corresponds to multiplying by 10^-1 or 0.1. So -3dB corresponds to multiplying by 10^-0.3 or about 50.1%.

Peter

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#231949 - 25/10/2004 13:36 Re: Experiences with Auto EQ [Re: peter]
genixia
Carpal Tunnel

Registered: 08/02/2002
Posts: 3411
No...

Quote:
Decibels (dB). A logarithmic representation of amplitude ratio, defined as 20 times the base ten logarithm of the ratio of the measured amplitude to a reference.


dB = 20 log (Vx/Vref). In this instance, Vref = 1, dB = -3
-3/20 = log Vx
Vx= 10^(-0.15) = 0.70795

Bizarrely, I think that I've often seen that rounded to 70.7%, even though it should be 70.8%. Maybe it's because it's so close to root 2.

For reference, this is when talking about voltage or current. When talking about power the equation changes and becomes 10 log (Vx/Vref) as you expected.

Let's say that you have an amplifier driving a speaker. The power from the speaker is given as V^2/R. So let's look at our power at that -3dB point relative to the peak;

Now at this -3dB voltage point, the power generated in the speaker is (0.708^2)/R = 0.501/R, ie half that generated at the peak. That is why the -3dB voltage point is also known as the half power point.

If we now look at the power equation:

dB(p) = 10 log ( Px / Pref )
dB(p) = 10 log ( 0.501 )
dB(p) = -3

So the -3dB point is -3dB regardless of whether we are talking about voltage or power, even though one is a function of the other squared. It also holds for current equations too, dB(I) = 20 log (Ix/Iref), as Power = I^2R.

Basically it all boils down to log a^b = b log a. The equations are different to give the same answer despite the square relationship between voltage/current and power.
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#231950 - 25/10/2004 14:10 Re: Experiences with Auto EQ [Re: genixia]
peter
carpal tunnel

Registered: 13/07/2000
Posts: 4148
Loc: Cambridge, England
Oh, OK. So the page should say something like "-3dB is 50.1% of 100% power, 70.8% of 100% amplitude"? That makes sense.

The bandwidth in octaves quoted for the car-player hardware EQ -- assuming it's the same as the Karma software EQ -- is between the points where the gain in dB is half that at centre. So the example I gave upthread is still right AFAICT.

Peter

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#231951 - 25/10/2004 21:44 Re: Experiences with Auto EQ [Re: peter]
SE_Sport_Driver
carpal tunnel

Registered: 05/01/2001
Posts: 4903
Loc: Detroit, MI USA
All of this is sorta over my head... but how does it all translate to getting proper EQ settings?
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#231952 - 25/10/2004 23:12 Re: Experiences with Auto EQ [Re: SE_Sport_Driver]
woops
journeyman

Registered: 24/04/2002
Posts: 78
i did autoeq using a computer mic (omnidirectional supposedly) and i must say the sound is SO MUCH better (i turned down the first two (bass) and the last (treble) bands just slightly) Thanks, SE_Sport_Driver, for the gift of making me aware, this really does make the empeg so sweet.

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#231953 - 25/10/2004 23:32 Re: Experiences with Auto EQ [Re: woops]
SE_Sport_Driver
carpal tunnel

Registered: 05/01/2001
Posts: 4903
Loc: Detroit, MI USA
As you can see, I havea lot of people to thank too!

The funny thing is that I started the page because my buddy moved away to Colorado recently. A few days before he left, we finally installed his empeg into his WRX. We never got a chance to tweak the sound on it.... next thing I know, I'm making a whole tutorial. I thought 20 or so people would be into it, but I'm surprised at all the views that thread has gotten!

As long as people are interested, I'll keep working on it.
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Brad B.

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#231954 - 05/03/2005 17:23 Re: Experiences with Auto EQ [Re: schofiel]
Jemmi
member

Registered: 03/05/2003
Posts: 131
Thanks so much for these instructions... I finally got around to doing this today. I'm amazed at the overall clarity even at high volumes. I added a 9db loudness boost and that is all and even music that my system sometimes had issues with (folk, bluegrass, some country - sparse instrumentation and bass mixed high) sounded perfect even when loud... and it was all so clear. I love it!

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#231955 - 13/03/2006 18:25 Re: Experiences with Auto EQ [Re: schofiel]
mcomb
pooh-bah

Registered: 31/08/1999
Posts: 1649
Loc: San Carlos, CA
Is anyone able to recommend a mic for this that is readily available in the US and matches the specs needed? I see that Brad linked a Radio Shack module that was said to work, but the link no longer works and he didn't give a part number. Also, can someone provide a link for the needed sound files?

Thanks,
-Mike
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#231956 - 13/03/2006 19:06 Re: Experiences with Auto EQ [Re: mcomb]
matthew_k
pooh-bah

Registered: 12/02/2002
Posts: 2296
Loc: Berkeley, California
Files.

Matthew

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#231957 - 13/03/2006 19:58 Re: Experiences with Auto EQ [Re: mcomb]
SE_Sport_Driver
carpal tunnel

Registered: 05/01/2001
Posts: 4903
Loc: Detroit, MI USA
Model 33-3013 Hands-Free Tie-Clip Omnidirectional Electret

The model number is "33-3013" and the cord is 3.3333 feet long. coincidence??

A write up may be coming on this soon... I'm using my 10gb player with 3.0alpha on it WAY more than my 160gb empeg these days so I'm itching to try it.

Basically though, turn off all sound modifications, (bass, eq, volume adjustments, etc, etc) and take the player out of shuffle. Clip the microphone to yourself, as close to your ears as possible. There is no point in making the EQ sound good for someone sitting in the dead middle of the car unless you plan on sitting there!
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Brad B.

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#231958 - 14/03/2006 00:12 Re: Experiences with Auto EQ [Re: SE_Sport_Driver]
mcomb
pooh-bah

Registered: 31/08/1999
Posts: 1649
Loc: San Carlos, CA
Thanks guys! I'll probably swing by Radio Shack on the way home and see if I can get this going.

-Mike
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#231959 - 14/03/2006 00:41 Re: Experiences with Auto EQ [Re: SE_Sport_Driver]
mlord
carpal tunnel

Registered: 29/08/2000
Posts: 13884
Loc: Canada
Quote:
All of this is sorta over my head... but how does it all translate to getting proper EQ settings?


All I can say is, Good Thing(tm) we had another (ex)Brit around to correct the (current)Brit! Us North Americans had no chance on this one.

Cheers

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#231960 - 14/03/2006 04:58 Re: Experiences with Auto EQ [Re: mcomb]
mcomb
pooh-bah

Registered: 31/08/1999
Posts: 1649
Loc: San Carlos, CA
Well, I tried to get this to work, but so far all I'm getting is silence. I believe I followed the directions exactly. I can play the noise files by hand, but as soon as I select AutoEQ it just sits there. No noise is played and it doesn't appear to be doing anything. The only thing I can think of is that I loaded the files with jEmplode (no windows box handy), is there any reason why that would matter? Any other suggestions?

Thanks,
-Mike
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#231961 - 14/03/2006 09:29 Re: Experiences with Auto EQ [Re: mcomb]
schofiel
carpal tunnel

Registered: 25/06/1999
Posts: 2992
Loc: Wareham, Dorset, UK
You have to select the files as a playlist before starting. Also, I found that the microphone connector was "jammed shut" - I couldn't insert the jack all the way in and I was scared of pushing it any harder without breaking. It did however suddenly "seat" properly and then started working. So I would suggest you:

- check the continuity of your microphone is OK
- unscrew the microphone socket on the harness and check the contacts are free to move
- that the contacts have continuity to the contacts on the harness connector in the sled.
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#231962 - 14/03/2006 12:43 Re: Experiences with Auto EQ [Re: mcomb]
SE_Sport_Driver
carpal tunnel

Registered: 05/01/2001
Posts: 4903
Loc: Detroit, MI USA
Quote:
Here's the story:

- downloaded the Auto EQ test audio files to a new playlist, and made sure they were ordered by using ALT-drag to set them sequentially in correct playback order
- synched
- went to the car and plugged in the mic, making sure it clicked home properly against the face of the socket on the harness (IMPORTANT!)
- positioned the mic next to my head over my shoulder
- turned on the ignition, turned off the ventilation and other noisy bits
- plugged in Erik the Empeg and waited to boot
- went into HiJack, turned off Bass and Treble adjust
- turned off Auto Level Adjust
- dropped out of HiJack
- using the rotary, turned off beeps, cross fade, loudness, and centred the fader and balance
- in the main menu, chose Playback and turned off Repeat, Shuffle, etc.
- went to the playlist with the auto EQ test files and selected them for play with the arrow (Play All) then hit pause.
- went to the equaliser
- selected an unused equaliser preset (#16 in my case)
- selected locks to be independent
- selected channels to be 2 (Stereo) (IMPORTANT!)
- set the volume to -30 dB
- held our breaths, and....
- selected Auto EQ and away we went!!!! (Rumble Rumble Whirr Whirr Wheee Wheee Hisss Hisss)


This is just part of the first post in this thread... I'd skim that post and the first few pages for anything that may have been missed (if any) when he first wrote that.
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#231963 - 14/03/2006 14:59 Re: Experiences with Auto EQ [Re: schofiel]
mcomb
pooh-bah

Registered: 31/08/1999
Posts: 1649
Loc: San Carlos, CA
Quote:
You have to select the files as a playlist before starting.

I did this.

Quote:
- check the continuity of your microphone is OK
- unscrew the microphone socket on the harness and check the contacts are free to move
- that the contacts have continuity to the contacts on the harness connector in the sled.


I did plug and unplug the microphone a couple times yesterday and it seemed to seat fine. Before I take my dash apart again to get to the mic jack doesn't the fact that microphone shows up as an audio source on the empeg imply that it is installed properly? Also, the empeg isn't even playing the tracks, why would this have anything to do with the mic?

Thanks for your help,
-Mike
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#231964 - 14/03/2006 15:03 Re: Experiences with Auto EQ [Re: SE_Sport_Driver]
mcomb
pooh-bah

Registered: 31/08/1999
Posts: 1649
Loc: San Carlos, CA
Quote:
This is just part of the first post in this thread... I'd skim that post and the first few pages for anything that may have been missed (if any) when he first wrote that.


I have read the entire thread. The only things that appears to have been mentioned later on are:

1. The empeg may be able to find the files on it's own without manually selecting the playlist. I tried this as well, didn't make any difference.

2. There are some additional audio adjustments that need to be turned off that Rob didn't mention.

It is certainly possible that my Rat Shack mic is dead, but wouldn't the empeg still play the files even without the mic?

-Mike
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