[music-dsp] analogue warmth?

Olli Niemitalo oniemita at mail.student.oulu.fi
Mon Jan 15 18:21:54 EST 2001


On Mon, 15 Jan 2001, Jon Watte wrote:

> Also, passband ripple from these filters is suggested as one contributing 
> factor to the inadequacy of current 44 kHz based players.

Yes, i've heard that with my own ears, nasty aliasing noise.... Don't know
if it's a big factor in spectrum-filled music though. I don't think there
are other problems, such as phase problems - modern DACs have symmetric
impulse responses in the audio range, and attenuation under 20kHz is
minimal.

> The problem is that we very seldom enjoy recordings of static sine waves. 
> The transients, glissandos and other variations found in music (live music 
> especially) can easily put spectral components of that 15 kHz signal towards 
> the Nyquist limit.

My hearing stops at 17.5kHz. Therefore, i'm not able to hear transient
variation caused by frequency components above that.

(The following might be a bit simplified, but the point stays)

In the ear, we have sort of bandpass filters. The response peak of a
filter is at the frequency observed by that particular sensor. The sensor
sends information about the output of the filter towards our brains. The
filter is not a "peak in the spectrum", it falls off to both directions,
allowing time localization of bursts of frequency. In order for a
sensor to be able to pick up a sound, the sound HAS to have frequencies
within the filter's band. The hearing frequency threshold (20kHz) is
set by the upper band limit of the highest tuned filter. If the sound has
frequencies above that threshold, they have no way to affect any sensor,
hence they will not affect the hearing sensation.

> And, indeed, a static sine wave is not the single frequency spike you'd think; 
> if that's what you want, you'd need to listen to a sin(x)/x signal...

Hmm, i don't get it -- can you explain? sin(x)/x has a brickwall spectrum,
but you say a spike?

-olli


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