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Topic: Octave band analysis (Read 4394 times) previous topic - next topic
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Octave band analysis

So I have this problem, I have my Ifuzen Amp for my headphones which allowes my headphones to play louder since they dont play loud enough off my iphone. But it changes the sound signature, so I had this idea of first using a sound level meter to make sure my headphones where playing at the exact same volume off my amp and off my iphone. Then measuring the difference the amp creates and adjusting the eq as such. However off of crappy computer speakers its obviously rather inaccurate. Im able to make sure the sound levels are the same by making sure the "max" is the same on the meter (Theres to values max and peak, I dont know which one to look at so I just chose max). But obviously each time the octave band analysis is totally different. Should I look at the "Peak" values of the individual bars instead of the "max" (I dont know what the difference is). Is there some more accurate special equipment I could buy?

Yes I realize the obvious answer is doing it by ear, but I don't think i'll be able to do that since if some random frequency is different it will seem "off" yet I won't be able to pinpoint exactly what it is. What do I do?

Octave band analysis

Reply #1
Can you feed the two sources into opposite sides of headphones? If the levels are balanced then the image should be centered in your head.

Octave band analysis

Reply #2
Can you feed the two sources into opposite sides of headphones? If the levels are balanced then the image should be centered in your head.


I don't understand what you mean.

This is one complicated and rather unclear question i'm sorry. So perhaps you misunderstood, or perhaps this is the solution but I simply don't understand, could you explain what you mean a bit more?

Octave band analysis

Reply #3
Can you feed the two sources into opposite sides of headphones? If the levels are balanced then the image should be centered in your head.

I see what you mean now, no, there's only one place you can put the plug into the headphone.

What do I do?

Octave band analysis

Reply #4
If you are using music with the SPL meter, that's not going to work.

If you make some test-tones (one for each EQ band) you should be able to get consistant, repeatable, readings.  For example, if you have a 10-band equalizer, make 10 test-tones and make 10 measurements without the amp and 10 with the amp.  Start in the middle (around 1kHz) and adjust the volume to match before messing with the EQ.  Then, by adjusting the EQ, you should be able to make the 10 readings match. 

Don't expect "flat" response, but you should be able to get the same response with, and without, the amp...  Headphones & speakers are never perfectly flat, and because of how headphones interact with the ear, they are hard to measure accurately.    And, your meter may not be flat.    You may have some trouble with the highest & lowest fequencies.  If you dont feel you are getting good measurements at very-high and very-low frequencies, make those adjustments (if needed) by ear.  It will also help if you clamp down the meter & headphones, or tape them together or something so that nothing changes/moves. 

Audacity (a FREE audio editor) can generate tones (Generate -> Tone -> Sine -> Frequency).

Don't make the test-tones too loud.  There is about 10 times as much power in a constant tone compared to music with the same peak, so there is a slight chance of damaging your headphones.    (If a 1kHz tone hurts your ears, it's probably too loud.)

Quote
Should I look at the "Peak" values of the individual bars instead of the "max" (I dont know what the difference is).
I don't know either...  Peak & Max seem like the same thing to me.  With constant test-tones, it might not make any difference.  What does the owner's manual say?    Maybe, "Max" is the long-term peak, held 'till you reset?  If there's an "Average" setting, use that with the test tones and you'll probably get more consistant readings

Quote
So I have this problem, I have my Ifuzen Amp for my headphones which allowes my headphones to play louder since they dont play loud enough off my iphone. But it changes the sound signature...
That really shouldn't happen.  Is there a difference when listening at the same volume?  The ear's frequency response is not "flat", but it changes and gets more-flat with increased loudness.    When you turn-up the volume, the bass sounds like it's turned-up more  (Equal Loudness Curves).

If there is a difference, usually it's the "non-amplified" device that has a problem...  If the souce impedance is too high, it can interact with the impedance of the headphone (which is not constant over the frequency range) to alter the frequency response.  Sometimes the response change is "desirable" (such a s a boost in mid-bass), but it's not "right".    However, it's my understanding that the iPhone & iPod don't have that problem.

P.S.
Be very careful if you test a regular speakers with test-tones!!!!
  The tweeter in a 100 Watt speaker might burn-out with a 10 Watt high-frequency test-tone, and it might not sound that loud to you, or you may not hear it at all!

P.P.S.
Here's another experiment you can try if you have a headphone Y-Adapter (for two headphones) and a 2nd set of headphones (or earbuds, etc.) -
- Connect the Y-Adapter to the iPhone, so that you can connect your headphones and the amp at the same time.
- Connect the 2nd set of headphones/earbuds to the amp and listen to them.
- Listen for a change in character (or "signature") from the amplifier when the (unused) headphones are plugged in-and-out of the iPhone.  If the sound changes, it's an impedance issue and the headphones are changing the signal coming out of the iPhone.

Octave band analysis

Reply #5
there's only one place you can put the plug into the headphone.

What do I do?

Plug this into your iPhone:

Connect one of the female jacks to your headphone amp input using this cable:

You will need two of these, one connected to the output of your headphone amp and one connected to the available female jack from the cable above:

Choose one channel (left or right; I will assume left for the rest of this post).
Connect the white female RCA connector from each of these to the the male RCA connectors of this cable (the red female connecters will remain disconnected):

Finally plug in your headphones and you're ready to go.

Caveat:
If your hearing isn't the same in each ear then this won't work very well.

Octave band analysis

Reply #6
[@DVDDoug:] Thank you very much! How should I go about getting the volume to match so that I can play the test tones then adjust the EQ to account for the difference between AMP and IPHONE? Because I need to see what the difference in sound is between the amp and iphone and adjust the EQ as such, but I can't make the tones the same volume because obviously i'm trying to find the difference in sound between the smp and iphone.

As for the person above me, those split cables are a good idea! But I don't understand how they will help with my problem, is the idea that I put one into the amp and one into the iphone and it should have the sound signature I like (the sound of the headphones plugged into the iphone, rather then the amp sound which changes the sound signature.) How does that work?

Octave band analysis

Reply #7
Quote
Thank you very much! How should I go about getting the volume to match so that I can play the test tones then adjust the EQ to account for the difference between AMP and IPHONE?
With the volume control.

For example -
- Play the 1kHz tone* without the amp and adjust for a good SPL reading, and note the reading.
- Play all of the other tones and note the readings

- Connect the amplifier.
- Play the 1kHz tone and adjust the volume down to match without the amp.
- Don't touch the 1kHz EQ slider.
- Play the other tones & adjust the associated EQ sliders to match the non-amplified readings.

Now...    Using that EQ adjustment when you use the amp, you have the same frequency response with and without the amp!


Quote
As for the person above me, those split cables are a good idea! But I don't understand how they will help with my problem,
The idea is to split the left & right signals (where they have separate connections at the red & white RCA connectors) so that one channel runs through the amp and the other does not.  ...I'd have to draw a picture fo figure-out the details.

Again, you'd have to match the volume (by ear).  If the amp has it's own volume control you can use that, otherwise you'd have to use the balance control.

Then adjust the EQ of the amplified channel (by ear) for matching signature/character in both ears.

This assumes you can adjust the EQ of the left & right channels separately (I don't know, I don't have an iPhone).   

It would be best to use a mono file so that both channels are getting the same sound.  You may not have any mono files, so unless the iPhone has a mono setting (again, I don't know,), you can convert files to mono with an audio editor (Audacity, etc.).


* I am assuming your EQ has a slider for 1kHz.  If not, choose a reference frequency that matches an EQ slider somewhere near the middle of the audio range.

Octave band analysis

Reply #8
I get it now. Thank you so much its very smart! I suppose I would have to make a file out of the tones and save it on the iphone for playback, right?

 

Octave band analysis

Reply #9
I suppose I would have to make a file out of the tones and save it on the iphone for playback, right?
Yes.  And, the process would be easier if you make a seperate file for each tone.