Some day in the past I've started to test different kinds of sound cards
and collect that information. It has been necessary personally for me to know
what a particular sound card is worth of, and so I've been able to make
suggestions of its use to certain people who appreciate my opinion. Therefore,
I've decided to get those figures and screen shots all together and turn them
into some order while adding new still. The last two ones have been tested in
January of 2005, and I have had frozen the project since.
(1-Jan-2007, update): All screen shots have used to be 960x720 32-colour
GIFs for a long time until they've got converted to PNGs to reduce their size
by approximately 40%.
All sound cards have been tested in the same environment, I mean inside
the same machine which I eventually happen to use for the last 5 years (since
1999) as a personal workstation, so results are fully comparable. The testing
suite is fairly simple: analogue loopback, i. e. the primary linear
output is connected directly to the primary linear input of a particular card,
some test tones are played and recorded, further processed with a FFT analyser
(SpectraLAB) using 16K FFT size to get some useful information. No hard
feelings or preconceived attitude, I've tried to benchmark every card to the
The tests include flat-weighted SNR (Signal to Noise Ratio),
THD (Total Harmonic Distortion), THD+N (Total Harmonic
Distortion + Noise) and IMD (InterModulation Distortion). For the first
three, a 1kHz sine waveform with -1dB amplitude has served as a source signal,
for the last one — a complex sine waveform of 250Hz -3dB and 8020Hz
-15dB. All waveforms are 44100Hz 16-bit stereo.
SNR (also known as S/N) is used often to demonstrate how
much noise a particular unit carries. To obtain, it's usually enough to set
volume controls to certain power level (for example, +4dBu), make sure there
is no signal applied (but all necessary equipment is connected and powered),
measure a noise level and divide one by another. Expressed in decibels. Should
be flat-weighted (in other words, without any noise shaping) on full 22kHz
range — 20kHz is considered to be the uppermost frequency recognised by
human ear, though some people cannot distinctly hear even beyond 16kHz; on the
other hand, some investigations have proved that tones beyond 20kHz are sensed
and used by subconscience for space orientation, like bats have but much
weaker; additional 2kHz are used mostly by low-pass filters to take effect
without attenuating frequencies close to 20kHz. Some manufacturers may prefer
A-weighting, i. e. noise shaping adaptive to human ear, but it's just a
trick to achieve higher figures for better sales without improving products
actually. Of course, higher results are better.
THD is a form of non-linear distortion. It takes into account
harmonics related to input signal as they appear in output spectrum. In other
words, if input signal contains a prominent frequency of X Hz, then
frequencies of 2*X Hz, 3*X Hz, 4*X Hz and so on are
checked and counted towards distortion. So, rms voltage of these harmonics is
divided by rms voltage of a prominent frequency and expressed in percent.
Lower results are better.
THD+N is very much like THD, but it checks for all harmonics that
appear in output spectrum, not only for related to input signal. Thus, it
takes into account other noise sources as well. Like THD, lower is better.
Note that flat-weighted SNR and THD+N are basically the same, with the only
difference that the first is expressed in decibels while the second is in
There are two distinct kinds of IMD, by SMPTE (Society of Motion
Picture and Television Engineers) and by ITU-R (International
Telecommunications Union, Radiocommunications division). The most commonly
used one is that of SMPTE, so let's follow it as well. It shows how one
frequency within signal given affects another within the same signal.
Frequencies are supposed to be clearly low and high, correlating as 4:1
(12dB). Though the frequencies may be any reasonable, SMPTE insists on 60Hz
low tone and 7kHz high tone, while DIN assumes 250Hz low and 8kHz high. I've
followed with the DIN frequencies. The output signal is checked for modulation
of the high frequency by the low one, i. e. an area centred at the high
tone is presented as consisting of multiple bands as wide as the low tone,
then rms levels of all bands except the central one are summed up, divided by
rms level of the high frequency and expressed in percent. Lower is better.
Having finished with theory, let's get to actual cards.