Topic: V3 HPF Internal Jumpers

[nedstruzz]

Anyone ever run the 12db per octave Active slope?  Any thoughts?

I've heard of the Thompson Butterworth method but it was a long time ago, any insight before I hit Google?

[DSatz]

I always use the V3 with 12 dB/octave low cut filtering either at 50 or 100 Hz. A 6 dB/octave rolloff is just "turning down the bass," not filtering noise out.

[nedstruzz]

Interesting, I tried to do a bit of research via Google and not much came up.  I appreciate the response. 

[Lil Kim Jong-Il]

I always use the V3 with 12 dB/octave low cut filtering either at 50 or 100 Hz. A 6 dB/octave rolloff is just "turning down the bass," not filtering noise out.

When you mention using HPF to cut noise, I think of handling noise or wind.  If someone is interested in just attenuating bass during an ambient recording on a fixed stand, would 6db down be a good balance between full on thumping bass and elimination of the lowend?

[DSatz]

> When you mention using HPF to cut noise, I think of handling noise or wind.

Well, using a low-cut filter for wind noise is often a devil's choice--the noise tends to be so broadband that you often have to cut the whole low end just to keep the wind noise down to an acceptable level. You really need to prevent wind noise (i.e. at the microphone), rather than recording it and trying to fix it later. It's not a minor problem in sound recording; it's a fundamental one, and calls for a fundamental solution, not a cosmetic one.


> If someone is interested in just attenuating bass during an ambient recording on a fixed stand, would 6db down be a good balance between full on thumping bass and elimination of the lowend?

Potentially, yes--but it would be far better to make this type of decision afterward in post production. You only have a small number of available choices built in to the preamp; you can't be fiddling with the jumpers during a live recording and guessing which setting to use based on headphone monitoring.

[nedstruzz]

I think I would be most interested to see what the slope looks like on a graph above 50hz at -6db per octave vs. 50hz at -12db per octave.

I am not so worried about what happens below 50hz as I am conerned with what happens above 50hz.

[JasonSobel]

I think I would be most interested to see what the slope looks like on a graph above 50hz at -6db per octave vs. 50hz at -12db per octave.

I am not so worried about what happens below 50hz as I am conerned with what happens above 50hz.

how far down at 50Hz depends not only on the slope of the HPF, but also the starting point.
in addition to internal jumpers for 6dB/octave vs 12 dB/octave, there are also internal jumpers that let you choose the starting points.  The two choices for the front HPF switch can be set to 100Hz and 50Hz or the two choices can be set for 125Hz or 75Hz.  so take that into account when figuring out what HPF looks like above 50Hz

[nedstruzz]

Yes, I am thinking that I would rather have -12db per octave at 50hz rather than -6db at 75hz but it would be really nice to see both on a graph.  I'll call Grace later today to see what they say. 

My reasoning is that rarely do I see a need to have anything below 50hz.  I typically roll it off in post anyway.  If having a better slope allows me to get better sound/level to tape then that is my ultimate goal. 

[DSatz]

> how far down at 50Hz depends not only on the slope of the HPF, but also the starting point.

No, actually when someone says that a filter is "at" 50 Hz, you know (if they're telling the truth and they know what they're talking about) that the response is down 3 dB at 50 Hz. That is true regardless of the filter's slope.

[JasonSobel]

DSatz - very good info, I wasn't aware of that.

even so, the starting point should definitely be taken into consideration. how much attenuation at 50Hz would be different if the filter is "at" 75Hz or if the filter is "at" 100Hz.  So that's one more variable in addition to the slope of the curve to be considered.

[NOLAfishwater]

I always use the V3 with 12 dB/octave low cut filtering either at 50 or 100 Hz. A 6 dB/octave rolloff is just "turning down the bass," not filtering noise out.

Thanks DSatz gonna open mine up tonight and try those settings out. I wonder how it is set when it comes from Grace. also, what is the difference for the A/D jumper that says PRO or CONS. Is that its frequency response?

http://www.gracedesign.com/support/v3_manual_RevE_online.pdf

[Todd R]

I always use the V3 with 12 dB/octave low cut filtering either at 50 or 100 Hz. A 6 dB/octave rolloff is just "turning down the bass," not filtering noise out.

Thanks DSatz gonna open mine up tonight and try those settings out. I wonder how it is set when it comes from Grace. also, what is the difference for the A/D jumper that says PRO or CONS. Is that its frequency response?

http://www.gracedesign.com/support/v3_manual_RevE_online.pdf

The PRO vs CONS jumper is for setting up the particulars of the AES digital out data stream (on only one of the AES outputs, I forget which).  It changes the data stream to one that fits the consumer (spdif) standard or professional AES standard.  The other AES output always provides the actual AES standard data stream, and the coax/spdif out always provides the consumer (spdif) standard data stream.  Somewhat important to know that even if you set the jumper to CONS, it provides only the consumer data stream, it does not affect the electrical signal, so the electrical signal still follows the AES standard (something like 10v for a digital "1" vs 0.5v under the spdif standard?  really can't remember the exact voltages).

On the HPF settings, the cutoff frequency is as DSatz mentions a knee point at -3db.  The slope is x db per octave, theoretically a linear slope.  So 50hz/12db is -3db at 50hz, -15db at 25Hz (-27db at 12.5Hz).  75Hz/6db is -3db at 75Hz, -9db at 37.5Hz, -21db at ~19Hz. 100Hz/6db would be -3db at 100hz, -9db at 50Hz, -16db at 25Hz. Etc, etc.