10 Jun
2010
10 Jun
'10
12:10 a.m.
On Wed, Jun 09, 2010 at 02:34:04PM -0700, Niels Mayer wrote:
Turning down the source by a dB or two should cure that.
I actually checked that peak at 116hz and figured it
couldn't be the
rectified result of the US-grid 60hz AC. That means we'd be running at
58Hz. ?? Since that's unlikely, what's the likelyhood of a 2hz
frequency error in jaaa??
Zero. By design. It's not 'calibrated', it's just maths.
Anyway you can test this quite easily. Connect a cable
to a line input, and touch the 'tip' of the other end
with your finger. This produces more than enough mains
to show up in JAAA.
Of course what JAAA shows depends on the accuracy of
the sample frequency.
'Canonical' settings for this chip are 0x7F (127) for input and
output. The range 128-163 is used by some cards to control additional
input gain.
127 causes clipping. How old is too old for a decoupling electrolytic??
Impossible to tell, there's too much spread in quality.
Some are defective from the start :-)
How much bandwidth does the op-amp have, and how much
negative
feedback is being applied?
Small-signal bandwidth and SR are not necessarily related
in simple ways.
But a wide-bandwidth op-amp is going to be
intrinsically noisier.... and a quiet op-amp is going to be
intrinsically slower,
No, there's no such simple relation.
But IIRC, the SR of the opamps you mentioned isn't really
exemplary, something in the 1-2 V/us range.
However in this case, my hypothesis is simple. No
handwaving,
hermeneutics or mysticism is needed. Coupling capacitors induce a low
frequency phase shift that is usually ignored because "engineers"
incorrectly care only about real-plane/power information; it is
misguided to think that humans cannot perceive phase information and
"imaginary plane" information.
The caps remain the first suspects, I agree. OTOH, for 'simple
circuits' such as an RC filter consisting of an electrolytic
and an input impedance, the amplitude and phase responses are
not independent. If there is really a problem with this then
it should show up in both.
More simply put, in reproducing a picked electric
bass, you expect the
the "pick noise" (high frequency) to arrive at the exact same time as
the the onset of the low-frequency fundamental of the note. The
coupling capacitors delay this onset.
Yes, but again a 'simple circuit' can't do this without at the
same time affecting the amplitude responses.
What is much more likely with defective caps is some 'delayed'
response which would actually make it non-linear as well, so
it will show distortion as well.
More interestingly, since I'd rather get away from
the subjective and
back towards the measurable, what kind of tests would be an
appropriate predictor for the "bass punch" of a soundcard? Certainly
not the frequency response or noise characteristics.
Well, if a circuit is linear (i.e. it doesn't produce distortion),
and time-invariant (it doesn't change its response over time,
except maybe *very* slowly), then either the impulse response
or the *complex* (including phase) frequency response will tell
you all there is to know. If you dispute this you have to talk
to the mathematians :-)
A 'magnitude only' frequency response, which is what you usually
get and also what JAAA provides, throws away half of the available
information. OTOH, in 'simple' circuits the phase response will be
related to the magnitude response.
Ciao,
--
FA
O tu, che porte, correndo si ?
E guerra e morte !