To Amp or Not to Amp: Apple i-device Sound Quality Tests
--------------------------------------------------------

Today I performed some experiments using the iPod
Touch, iPhone4, and desktop computer running iTunes,
to determine sound quality differences with and without
various EQ's enabled. When using iTunes on the desktop
and the Shure 1840 headphone, I settled on the "Bass
Booster" setting of iTunes, which raises the curve
by one db at 500 hz and 5 db at 32 hz, with a smooth
gradient between those points. Switching the equalizer
On and Off while music is playing makes for a subtle
difference with most tracks, taking into account the
delay while iTunes buffers the data it's going to be
dithering. Interestingly, the overall volume doesn't
seem to change when EQ is turned On and Off.

When using the built-in music player on the iPod/iPhone
and the same Shure 1840 headphone, I also selected the
"Bass Booster" setting, but in this case the volume
changes quite a bit, requiring fast fingers to adjust
it back up when EQ is turned On, and back down when
EQ is turned Off. But whereas the signature change
is subtle (and correct) on the desktop iTunes, it's
dramatic with the iPod/iPhone, and probably at least
double what the desktop EQ screen indicates. I'd guess
that Apple expects their little pocket-size iPod/iPhone
players to be used in noisy environments, and so they
probably make the EQ adjustments larger to compensate
for the noise.

When using the iPod/iPhone with various analog headphone
amps via the LOD dock connector, the EQ settings work
the same way as when using the headphone from the iPod/
iPhone headphone jack, and the changes to the sound are
about the same, taking into account the relatively small
changes that the headphone amps contribute themselves.
One fact becomes clear in doing these tests, and that
concerns the arguments about dramatic differences in
sound when switching from the iPod/iPhone alone to a
headphone amp, or using headphone amps that are said
to be a better match for a given headphone than other
competing amps. Here are a few of my observations:

1) The differences in sound between various high-quality
headphones are far greater than the differences between
headphone amps, for amps that are performing properly
with the headphone being used. There are good and useful
definitions of "high fidelity" in the industry now, but
these often-dramatic differences between headphones are
not due to a failure of convergence around high fidelity
standards, or "personal preference". Most often they're
the result of deliberately planned distortions to pander
(i.e. market) to "modern" tastes. If you happen to like
the sound of today's Top 40, you're in luck.

2) The overwhelming majority of headphone listening is
done these days in "distracted" mode - gaming, watching
movies, cruising the Internet etc. This begets an aspect
of the Fletcher-Munson (equal loudness) effect, where
low-volume listening makes bass and treble (especially
bass) seem weaker than at normal volumes. I've observed
this effect in my own music listening.

3) Playing music for several minutes with a good quality
amp and then switching to the iPod/iPhone alone, you'll
hear the loss of quality - of "air" especially, and it
may seem dramatic. But going the other direction, the
difference always sounds subtle to me, so I doubt that
the difference per the first example is actually more
than subtle. The iPod/iPhone, while limited in volume
and dynamics for inefficient headphones like the Shure
1840, nevertheless provides a similar tonality, sound
signature, and freedom from distortions as any of the
good headphone amps, albeit differences in soundstage**,
"air", bass tightness, and other characteristics may be
audible.

**Soundstage, like some other sound characteristics,
may be enhanced or diminished with different amps,
not because of some inherent audio superiority in
that amp, but because other things can change that
affect users' impressions of soundstage. Channel
separation in some unbalanced systems, power supply
interference, and various other factors are just some
of the places to look. And this isn't about "amping"
per se, it's about quality and attention to detail.
It's no coincindence that the iPod/iPhone sounds as
clean and stable as it does, and the fact that it runs
off of a good quality battery rather than an AC mains.

4) The iPod/iPhone doesn't have nearly the performance
capability of an average desktop or laptop computer,
and I expect that opinions of its vast inferiority
compared to desktop players are prejudiced on that
fact. But if you look at what Dirac accomplished with
their very advanced DSP's for earbuds, earpods and now
several different IEM's, I think you can appreciate
just how much excess capability the iPod/iPhone has
that isn't being used in normal playback with 320 kbps
MP3's, given the maximum volume limitation of course.

5) Listening conditions are a much larger factor in the
perception of sound quality than amping. Listening out
of doors where noise levels are high will mask a lot of
detail, and even when listening indoors, such as late at
night compared to daytime listening, the ambient noise
level can be as much as 20 db lower, exposing much more
detail in the sound. Using closed headphones may reduce
the deleterious effects of daytime noise levels, but
most closed headphones introduce their own less-than-
desirable effects, so that's not an ideal solution.

6) "We all hear differently" is often cited as a reason
why headphones sound so different from each other, and
why users are spending big money on amps, hoping that
those amps will make their headphone colorations more
musical somehow. When we sit together at a live music
event, we hear the same thing. If we hear it differently
in our individual sets of ears, and assuming we don't
have any significant hearing damage, then there should
not be a need for large differences on playback systems
when the only adjustment for live music is to move away
from the sound or use earplugs.