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Old 11th June 2008, 09:17 PM   #21
sek is offline sek  Germany
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The above pictures have been image processed for quick readability even as a thumbnail. The test signal we see is a 1kHz sinus at 0dBFS. I've tried different (digital) dBFS levels and it appears the maximum level on the headphone out really is software limited.

Please correct me on any mishap with the calculations.

In order to do a quick test, generate a 50/60Hz or 100/120Hz sine wave signal, embedd it into iTunes as a WAV file and synchronize it to your iPod. Then connect a regular multimeter (frequency dial) with the help of an open mini plug or a special test cable. The reading should show an accurate figure of your iPod's maximum RMS output level (for sinusoidal signals) which you can then use to calculate dBu figures. You may of course also employ a true RMS meter.

Cheers,
Sebastian.
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Old 12th June 2008, 01:37 PM   #22
gain is offline gain  United States
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i don't know what all this Urms, VP, LP, etc means.

an ipod has a audio amp in it. all audio amps have peak voltages they are capable of delivering to the load. it is usually measured in +/- Volts RMS.

would think it would be clearly specked out? maybe not.

can anyone here answer what the max RMS voltage output of an ipod is or do i have to drive 45min to a lab with a scope and measure myself. from the experimenting/playing i've done so far i can be certain the ipod's output is much less than line level (maybe like 250mV - 500mV).

thanks.
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Old 12th June 2008, 01:40 PM   #23
gain is offline gain  United States
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just reminded me of a quote from an old teacher,

"the nice thing about standards is there is such a variety of them to choose from."
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Old 12th June 2008, 01:43 PM   #24
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by sek
In order to do a quick test, generate a 50/60Hz or 100/120Hz sine wave signal, embedd it into iTunes as a WAV file and synchronize it to your iPod. Then connect a regular multimeter (frequency dial) with the help of an open mini plug or a special test cable. The reading should show an accurate figure of your iPod's maximum RMS output level (for sinusoidal signals) which you can then use to calculate dBu figures.
Hi Gain,
Sek tells you how to do it without a scope.
50Hz to 120Hz can be measured with an analogue or digital multimeter.
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Old 12th June 2008, 02:51 PM   #25
gain is offline gain  United States
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i dont know what anything sek is saying. i don't even own a scope, let alone sophisticated computer measuring equip like he suggests using.

basically i want to make a attenuator/booster so i can convert the ipod voltage output level to line level RCA so i can connect it to a stereo. like cd, tv, vcrs, etc all put out about ~1VRMS. ipods put out something different than ~1VRMS. what does an ipod put out? from experiment in my basement i have found it to be about 1/2 - 2/3 the voltage signal output of a cd player.

does this clarify my question? its not that i dont want to take your advise, just dont have thousands of dollars to spend on computer equipment right now. can someone please just tell me "the analog output of an ipod through its 1/8 stereo female is XYZmV)

thanks.
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Old 12th June 2008, 03:13 PM   #26
AndrewT is offline AndrewT  Scotland
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Hi gain,
you're sitting at a computer, I'll bet it is already capable of creating that 0dBfs file that Sek talks about.
I suspect you have a DMM.
You only need to do some reading and ask the right questions if the literature is beyond comprehension.
He is not asking you to spend any money. Simply to use your brain.

Go Read.
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Old 12th June 2008, 03:18 PM   #27
gain is offline gain  United States
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i'll go measure, experiment and speak with other experts. i'll also give up hope of getting a straight answer on this thread.
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Old 12th June 2008, 03:21 PM   #28
sek is offline sek  Germany
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Quote:
Originally posted by AndrewT
Sek tells you how to do it without a scope.

He is not asking you to spend any money. Simply to use your brain.
Thanks for the heads up, Andrew.


Quote:
Originally posted by gain
i don't know what all this Urms, VP, LP, etc means.
The symbol U is derived from lat. urgere (to urge, push, press) and is the old fashioned way of designating a Voltage. The international SI unit is V, which some researchers critizise (due to it's ambiguity). That still leaves us with L, which stands for the level.

So all you are looking for is in the above posts. You know what the character '≈' means, right?


Quote:
would think it would be clearly specked out? maybe not.
Not with Apple.

iPods are consumer products. They rather not specify it at all than risk a comparison with the competition.


Quote:
i don't even own a scope, let alone sophisticated computer measuring equip like he suggests using.
Erm, hello?

I'm trying to explicitly telling you how to do it with a regular computer and without a scope here!

By signal generator I of course mean free software for you to download. Google is your friend.


Quote:
ipods put out something different than ~1VRMS. what does an ipod put out?
Let me repeat for you: ≈ 0.33Vrms But please keep in mind that this may not apply to all iPods.

Take a look at this Voltage and Level Converter in order to compare this to the other numbers I gave you.

No, wait. I'll do it for you!

1Vrms = 0dB(V).

0.33 Vrms ≈ -9.5dB(V).

So in order to elevate the iPod's output level to your desired input level you need a gain stage with a gain of a ≈ +3 or (in other words) a ≈ +9.5dB (without V ).

Why? Because 1Vrms ≈ 3 * 0.33Vrms. And also because 0dBV - (-9.5dBV) = +9.5dB (without V).

I leave it on you to repeat the calculation for the line level I measured.
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Old 12th June 2008, 03:29 PM   #29
gain is offline gain  United States
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Quote:
Originally posted by sek

Let me repeat for you: H0.8Vrms

thank you, sek. all i wanted to know.
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Old 12th June 2008, 03:35 PM   #30
sek is offline sek  Germany
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Aaaah! I corrected a wrong number while you've been reading!

It's 0.33Vrms, look again.

I had iPod and Dock output levels confused... Sorry!
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