Rx/Tx equalization band selection

[Mike Scott-7]

After plotting filter response on my 2.7 KHz filter
I have been thinking about the Rx/Tx eq settings.

The current equalization scheme is 7 octave bands at: 50 Hz, 100 Hz, 200 Hz,
400 Hz, 800 Hz, 1600 Hz, and 3200 Hz plus an interloper non-octave band at
2400 Hz. I can guess why these bands, they match a popular external
microphone equalizer product.

My filter is down 20 dB at approximately 100 Hz (from zero beat.) This
number is from graphical construction where I only took data points every
100 Hz and plotted the results.

It would appear that the bottom equalizer band is beyond useful. Even with
maximum equalization gain the 50 Hz spectrum is still way down. This tells
me that we don't really have an 8-band equalizer as only 7 bands have
utility. The 100 Hz band is questionable but barely within the zone.

Perhaps Wayne is going to open the lower end some more and then my issue
could become moot and everybody would have to go buy a woofer. However
whenever I try to equalize waterfall speckling I wish I had more granularity
in the useful part of the audio spectrum.

If we wanted to start at 100 Hz and split the band between 100 Hz and 3200
Hz into 7 equal fractional octave bands then sub octave processing would do
that with band centers of 100, 178, 317, 566, 1008, 1796, 3200; then keeping
with the theme, throw in an interloper band around 2400 or someplace useful
to make an 8-band processor. The octave band centers above are 100 Hz
multiples of the 6th root of 32 (3200/100.) The current scheme is 50 Hz
multiples of the 6th root of (3200/50) which is the magical 2 factor.

Starting at 150 Hz instead of 100 (my favorite) may also make sense leading
to band centers of: 150, 250, 416, 693, 1154, 1921 and 3200 with an extra
one at 2500. Since these are broad anyway, why not call them 150, 250, 400,
700, 1200, 1900, 2500 and 3200 and give people the option of maintaining the
current scheme or shifting to one of these? I kind of like having one of the
filters centered on 700 Hz anyway.

My 2 cents


Mike Scott - AE6WA
Tarzana, CA (DM04 / near LA)
K3-100 #508/ KX1  #1311


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[Don Wilhelm-4]

Mike,

All that effort may be an exercise in futility.
If I read your report correctly, you measured the roofing filter only.
The full story is with both the roofing filter and the DSP filter
engaged.  That will tell the story about what you hear, not just what
the input to the DSP looks like.

73,
Don W3FPR

Mike Scott wrote:

> After plotting filter response on my 2.7 KHz filter
> I have been thinking about the Rx/Tx eq settings.
>
> The current equalization scheme is 7 octave bands at: 50 Hz, 100 Hz, 200 Hz,
> 400 Hz, 800 Hz, 1600 Hz, and 3200 Hz plus an interloper non-octave band at
> 2400 Hz. I can guess why these bands, they match a popular external
> microphone equalizer product.
>
> My filter is down 20 dB at approximately 100 Hz (from zero beat.) This
> number is from graphical construction where I only took data points every
> 100 Hz and plotted the results.
>
> It would appear that the bottom equalizer band is beyond useful. Even with
> maximum equalization gain the 50 Hz spectrum is still way down. This tells
> me that we don't really have an 8-band equalizer as only 7 bands have
> utility. The 100 Hz band is questionable but barely within the zone.
>
> Perhaps Wayne is going to open the lower end some more and then my issue
> could become moot and everybody would have to go buy a woofer. However
> whenever I try to equalize waterfall speckling I wish I had more granularity
> in the useful part of the audio spectrum.
>
> If we wanted to start at 100 Hz and split the band between 100 Hz and 3200
> Hz into 7 equal fractional octave bands then sub octave processing would do
> that with band centers of 100, 178, 317, 566, 1008, 1796, 3200; then keeping
> with the theme, throw in an interloper band around 2400 or someplace useful
> to make an 8-band processor. The octave band centers above are 100 Hz
> multiples of the 6th root of 32 (3200/100.) The current scheme is 50 Hz
> multiples of the 6th root of (3200/50) which is the magical 2 factor.
>
> Starting at 150 Hz instead of 100 (my favorite) may also make sense leading
> to band centers of: 150, 250, 416, 693, 1154, 1921 and 3200 with an extra
> one at 2500. Since these are broad anyway, why not call them 150, 250, 400,
> 700, 1200, 1900, 2500 and 3200 and give people the option of maintaining the
> current scheme or shifting to one of these? I kind of like having one of the
> filters centered on 700 Hz anyway.
>
> My 2 cents
>
>
> Mike Scott - AE6WA
> Tarzana, CA (DM04 / near LA)
> K3-100 #508/ KX1  #1311

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[Jim Brown-10]

On Sat, 23 Aug 2008 16:03:40 -0700, Mike Scott wrote:

>band centers of: 150, 250, 416, 693, 1154, 1921 and 3200 wit

The centers of audio filters in octave, half-octave, one-third
octave, and one-sixth octave increments were standardized many
years ago by scientists and engineers working in audio and
acoustics. Unlike the communications standard for the audio
bandwidth of communications systems, these are excellent standards
that take into account how humans HEAR sound. We tamper with these
standards at our own risk.

>It would appear that the bottom equalizer band is beyond useful.
>Even with maximum equalization gain the 50 Hz spectrum is still
>way down. This tells me that we don't really have an 8-band
>equalizer as only 7 bands have utility. The 100 Hz band is
>questionable but barely within the zone.

50 Hz and 100 Hz octave bands are VERY important -- they allow
equalization to correct for proximity effect in directional
microphones, and to reduce the effects of breath pop. The octave
bands below 500 Hz contribute little to communications. If allowed
to modulate our transmitters, they waste transmitter power. The
best designers of sound systems for reverberant spaces know this
well -- we carefully roll off the low end of speech systems for
big churches beginning somewhere between 200 Hz and 300 Hz.

73,

Jim Brown K9YC




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[Barry N1EU]

Jim Brown-10 wrote

50 Hz and 100 Hz octave bands are VERY important

Why is 50hz important if it is completely outside the passband? +/-16dB at 50hz has zero effect on rx or tx in the K3.

73,
Barry N1EU

[Jim Brown-10]

On Sun, 24 Aug 2008 14:41:54 -0700 (PDT), Barry N1EU wrote:

>Why is 50hz important if it is completely outside the passband? +/-16dB at
>50hz has zero effect on rx or tx in the K3.

Don't be so sure that there's no effect. It's important that when this
undesired low frequency energy is produced by the mic, it is not carried
through AUDIO path where it can trigger limiting, create distortion, or even
cause overload. On the air, especially during contests, I hear lots of low
frequency trash on SSB signals, most of it room noise.  

In general, if the desired bandwidth of a system is limited, as ours is, the
modulating signal (in this case, microphone audio) should be bandwidth-
limited as early in the signal chain as practical. Many good mics have
built-in high pass filters or low-frequency roll-off filters. When I'm
mixing live program material, whether music or speech, I ALWAYS use a good
high pass filter on every microphone preamplifier. With most musical
instruments, it's set near 200 Hz. With instruments like a bass or bass
guitar, I'll move it down to 40 Hz or so.

73,

Jim Brown K9YC


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[Jim-168]

Low order distortion

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Jim Brown
Sent: Sunday, August 24, 2008 6:28 PM
To: Barry N1EU; [hidden email]
Subject: Re: [K3] [Elecraft] Rx/Tx equalization band selection

On Sun, 24 Aug 2008 14:41:54 -0700 (PDT), Barry N1EU wrote:

>Why is 50hz important if it is completely outside the passband? +/-16dB at
>50hz has zero effect on rx or tx in the K3.

Don't be so sure that there's no effect. It's important that when this
undesired low frequency energy is produced by the mic, it is not carried
through AUDIO path where it can trigger limiting, create distortion, or even

cause overload. On the air, especially during contests, I hear lots of low
frequency trash on SSB signals, most of it room noise.  

In general, if the desired bandwidth of a system is limited, as ours is, the

modulating signal (in this case, microphone audio) should be bandwidth-
limited as early in the signal chain as practical. Many good mics have
built-in high pass filters or low-frequency roll-off filters. When I'm
mixing live program material, whether music or speech, I ALWAYS use a good
high pass filter on every microphone preamplifier. With most musical
instruments, it's set near 200 Hz. With instruments like a bass or bass
guitar, I'll move it down to 40 Hz or so.

73,

Jim Brown K9YC


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