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Tips on how to search for the frequency playback curve of MP3 players?

post #1 of 5
Thread Starter 
I'm looking for a spare MP3 player and was looking at the Cowon X7, but I can't find it's "frequency playback curve?" I'm not exactly sure if that is its proper terminology, but when I'm looking at some players that catch my interest, it's sometimes hard to find what that curve is.
post #2 of 5
Thread Starter 
How do I search for reviews like this but of all players?

http://nwavguy.blogspot.ca/2011/02/sansa-clip-measured.html
post #3 of 5
You're looking for frequency response graphs, for the output. Technically you're just looking at the frequency response magnitude and not phase; it's more common to find the magnitude plots. Nobody shows phase but not magnitude. Magnitude is what really counts anyway, at least in realistic scenarios for most electronics.

Most people writing about players don't bother with such tests. There isn't much published information on most players out there, same for most audio devices. A lot of times it's not a matter of you not being able to search but the information not existing out there.


Actually, it's not necessarily even that simple. If you're plugging some headphones (IEMs) into the player, what's of interest is the frequency response seen across the terminals of the headphones, as that's the signal that's driving the headphones. For some players, the response may be significantly different depending on what headphones you're using. This happens if (1) the headphones have a weird impedance that varies a lot over frequency particularly if the low parts are at low impedances and the player has a high output impedance and (2) if the player has a DC blocking capacitor (hence "infinite" impedance at DC... it's a high-pass filter that's cutting out some bass and not just 0 Hz) and the headphones have relatively low impedance.

So depending, even if you do find FR graphs, it's often just somebody testing with no load, and without testing to see the output impedance and so on. This means that even if you do find data, it could be incomplete and not even representative of the response you'll get when you plug headphones into the thing. (not the case if you use an external amp)


edit: I don't know about the X7 in particular, but some other Cowons do use a DC blocking capacitor on the output, and thus roll off bass several dB by 30 Hz or so (which is honestly pretty low, not that common), with 16 impedance phones. The higher the impedance, the less the rolloff.
Edited by mikeaj - 3/27/13 at 8:02pm
post #4 of 5
Thread Starter 
Thanks a lot for the information. Is there any benefits to DC blocking or does it just help in amperage sensitive headphones? I use the SM3v2s on a Sony Z-1060 with a line-out to a Fiio E11; which is overkill for the headphones. I use to use some IM716s but one of the channels died. The SM3s already are a few dB higher in the mid to lower mid range anyways, might flatten them out a bit.
Edited by Domino - 3/28/13 at 11:50am
post #5 of 5
First off, if you're not using the player's headphone output to drive headphones, you can (outside of academic interest) ignore everything said with respect to output impedance, DC blocking, and things being different with different headphones. You'd instead be looking at the same factors with the output of the amp you're using, not the output of the player. The considerations are primarily whatever is driving the headphones and whatever is doing the digital/analog conversion—though there's not much to go that wrong for D/A except maybe some noise / hiss, for modern audio electronics that are built sensibly.

Line-out to E11 means you can forget this stuff. E11 has low output impedance including at 0 Hz (DC)—no problems there. More or less, the input of an amp behaves electrically as a large impedance so there are few effects and interactions with respect to the player's output.

A DC blocking capacitor is used in this context as kind of an engineering compromise or solution. Pretty much, you don't want to output DC voltage into headphones, especially small IEMs, or you'll burn them up. More than some low tens of milivolts is maybe bad. Depends. There are various other ways to prevent DC from being output to the headphones, different amplifier designs that could be used. Most of the alternate schemes may require additional complexity, more parts, higher power consumption. Putting a capacitor on the output of the device means that if you plug in headphones, any DC that would have gone into the headphones, instead goes across the capacitor. The drawback is that you need a capacitor, there will be some amount of bass rolloff (less with a larger capacitance value), some amount of distortion (less with certain capacitor types). Because of size and cost limitations, electrolytics are usually used, but even then, they're usually too small in capacitance to avoid some non-trivial bass rolloff with 16-32 ohms headphones.
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