Here's a bit of an odd question. When headphones are measured for their frequency response, before the final graph is released, it is "corrected" based on the human hearing curve (since we don't hear everything at the same volume). Because of this, headphones are designed to be flat after this correction. Why would we correct a headphones measurement? An orchestra isn't going to compensate for your ear's frequency curve, why should a headphone designed to reproduce said orchestra do so?
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In a perfect world, if you measure a flat speaker in a anechoic chamber with a flat mic in place of your head you measure a flat frequency response. BUT if you measure at the eardrum inside a head with ears attached you will measure something that is not flat at all.
So some point in space, the sound source, produces sound -> your head-related transfer function (HRTF) "processes" the sound -> your brain interprets it.
Depending on the headphone, most of your HRTF may be bypassed* and the location of the sound source is fixed at +/- 90° (the drivers sit directly in front of you L/R ear). That needs to be corrected to achieve a frequency response at the ear drum that is similar to that from the perfect measurement above. Some of these correction curves are: free field, diffuse field, independent of direction, Olive/Welti ... equalization.
*) HRTF includes your shoulders, head, all the parts of your ear and changes with the position of the sound source
Edited by xnor - 11/5/13 at 2:40pm
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So essentially it's making up for the fact that the headphones are right next to your ears? That makes sense, thanks. One more question, though. I know the structure of the ear changes the way sound is perceived, are there different curves for IEMs as opposed to full-sized or on-ear headphones? Or is the difference the ear makes with a 90 degree point source minimal?
I recently stopped buying CD's. I mainly listen to music on the move and downloads make sense.
In fact I had long regarded CD as a rather poor medium. No one is going to get misty eyed about a CD cover.
I am nostalgic for the tactile nature of a vinyl collection but it would be very expensive and impractical at this stage.
In fact I have gone further and have a Spotify Premium account. I enjoy the fact that I have access to a phenomenal library of music and no physical media to clutter my life up.
I am aware of the problematic business model regarding the artist but that's another can of worms.
I am using my phone as a source. Portable amp and IEM's. All this is hardly high end audio but It fits in with how I listen to music these days.
I just wonder how good sound quality I can expect in this context.
All I can comment on is spotify:
Spotify uses 3 quality ratings for streaming, all in the Ogg Vorbis format.
- ~96 kbps
- Normal quality on mobile.
- ~160 kbps
- Desktop and web player standard quality.
- High quality on mobile.
- ~320 kbps (only available to Premium subscribers)
- Desktop high quality.
- Extreme quality on mobile.
160 kbps might have some audible artifacts with problematic tracks, but 320 kbps should be completely transparent.
I think Youtube's max audio bit rate is 192 kbps?
There are times it doesn't sound too different from a 320kbps, depending on the track. 320 should be more than sufficient.
No I meant like with downloads you don't even have a physical thing anymore, just a file. And with streaming it's just some bytes in volatile memory.
I guess so, if the video is HD. But it will go through at least one transcoding process, because youtube seems to transcode every video including (lossy!) audio.
I think my "problem" at the moment is simple. I don't like the sound of the iPhone 5S.
What I have taken from this exchange is that I will no longer think of digital as a poor relation to analogue quality wise. That's a big step forward for me I think. Thanks for all the info.