Topic: Quick Bass Rolloff question...

[justink]

i did a search but didn't find anything to help me off hand.

it's been a while since i dusted off the gear...  what's a good bass rolloff setting for a solo instore performance?  more Hz means more roll off correct?

i had it set at 160Hz for OAR and Howie Day the last time i ran this gear, but there was a TON of bass on the tape.  i'd like to avoid that.

so, the higher i have the Hz set at, the less bass on the tape?

 i'm planning on rocking the [sp omni's -> battbox (195Hz) -> d7] for Robert Earl Keen tonight, instore performance, that is if they let me in w/ gear.

thanks!

-j

[Tim]

so, the higher i have the Hz set at, the less bass on the tape?

yes

[goose]

I'm not positive, but I don't think the rolloff will be effective going line in, only mic in.  If you ran line in previously, you may have nullified the rolloff setting. 

I'm sure someone can confirm or correct my thoughts.

[justink]

I'm not positive, but I don't think the rolloff will be effective going line in, only mic in.  If you ran line in previously, you may have nullified the rolloff setting. 

I'm sure someone can confirm or correct my thoughts.

i've always gone line in on the d7 even w/ the mc012 ->mixpad ->d7

how would line in nullify the rolloff?  i always thought line in meant a direct line from the batbox, the only thing the d7 did was convert A/D and record?

[fandelive]

I'm not positive, but I don't think the rolloff will be effective going line in, only mic in.  If you ran line in previously, you may have nullified the rolloff setting. 

I'm sure someone can confirm or correct my thoughts.

the roll-off is effective going line-in, but the only usefull preset in this case is the 888Hz. (at least for "boomy" rooms)
I'd recommend you to check out this thread for more information :
http://www.taperssection.com/index.php?topic=5534.0

[jeromejello]

those of us using a jb3, the impendance is 37kOhm.

the break out becomes:
16Hz > 4.3Hz
69Hz > 18.7Hz
95Hz > 25.7Hz
107Hz > 28.9Hz
160Hz > 43.2Hz
195Hz > 52.7Hz
888Hz > 240Hz

the last couple of shows i taped with the 69Hz setting (actually 18.7)  i think its ok, but not as effective as it could have been in the tabernacle.  i think i am going to set it to 95Hz (25.7) or even 107HZ (28.9) for tonights gig.

the way i look at it is this... while not as effective as i first was lead to believe, the roll off (while i am still using this battery box - until you sell me your oade mod ua-5) should allow me to cut the low, low end, allowing a higher gain on the recording without clipping.  i know nothing though.

[justink]

would that be the same for the d7 also? 

so, since i'm running omni's i should keep it on 888Hz or the next one down?

[Weazel]

d7 line in impedance is 47 kohm

[cgrooves]

Mic-in frequencies (based on the pcm-m1 Mic-In resistance of 4.7 kOhm) :
  (16Hz) >  32Hz    2,3,4   
  (69Hz) > 138Hz   1,4   
  (95Hz) > 190Hz   1,3   
(107Hz) > 214Hz   1,3,4   
(160Hz) > 320Hz   1,2   
(195Hz) > 390Hz   1,2,4   
(888Hz) > 1776Hz 1,2,3   

Line-in frequencies (based on the pcm-m1 Line-In resistance of 47 kOhm) :
(16Hz) > 3.2Hz    2,3,4   
(69Hz) > 13.8Hz  1,4   
(95Hz) > 19Hz  1,3   
(107Hz) > 21.4Hz  1,3,4   
(160Hz) > 32Hz  1,2   
(195Hz) > 39Hz  1,2,4   
(888Hz) > 177.6Hz  1,2,3

Also valid for the d7 (or any other unit with a line-in resistance of 47 kOhm)

[inside source]

Ok, so when I see that the recording was made using:
"SP-CMC-8 > SP-SPSB-6 (rolloff @ 107 Hz) > PCM-M1 (line-in)"
does it mean that the bass rolloff was in fact not effective?! Considering that 107Hz/4.7=22.8Hz and frequency response for CMC-8 starts at 30Hz. And I might add that I see rolloff setting @107Hz into line-in quite often...

[cgrooves]

You've got it.  My chart is based off of a 10 kOhm resistance designed battery box translated to a 50 kOhm resistance line-in recorder. The m1's line in resistance is 47 kOhm, so the figures shown above are a little off. 

If you use the 195Hz setting, the roll-off is actually 41.5Hz Line-In on the m1. (Probably not enough roll-off for many situations)
If you use the 888Hz setting, the roll-off is actually 188.9Hz Line-In on the m1. (Too much roll-off for practically any situation)

Best thing to do with these mics is to go phantom, IMO, especially if using a Sony dat recorder. Phantom power will let you use these mics to their fullest range of SPL's.  Another option would be to alter your battery box so that the settings will be more useful to your recorder. You would think that they would offer this as an option on their battery boxes, rather than just building them based on a generic line-in resistance of 10 kOhm.

[inside source]

Thanks!

I compiled a quick table to see what are actual bass rolloff settings for various recorders.
Looks like this original bass rolloff option in SP battery box is in fact not useful for JB3 and DAT line-in, though people often use certain rolloff setting thinking it makes an effect, when actually it doesn't. For minidisc recorders it looks ok if the settings are doubled (see 160 Hz and 195 Hz option). I assumed that MD has 20 kOhm line input impedance, please correct me if I'm wrong. Is it correct for the new Hi-MD recorders? I didn't find it in the manual.

I borrowed the jumper settings from cgrooves post.

Table. Bass rolloff settings for line-in.
The values are rounded to the nearest number.

batt. box setting       MD          JB3         DAT
(based on 10kOhm)    (20 kOhm)   (37 kOhm)   (47 kOhm)

  16 Hz  -  2,3,4       8 Hz        4 Hz        3 Hz
  69 Hz  -  1,4        35 Hz       19 Hz       15 Hz   
  95 Hz  -  1,3        48 Hz       26 Hz       20 Hz
 107 Hz  -  1,3,4      54 Hz       29 Hz       23 Hz
 160 Hz  -  1,2        80 Hz       43 Hz       34 Hz
 195 Hz  -  1,2,4      98 Hz       53 Hz       42 Hz
 888 Hz  -  1,2,3     444 Hz      240 Hz      189 Hz

[dklein]

hey - nice chart.  Just for a reality check it might be worth checking the cap values that are being actually used (if you can see/read them)

[inside source]

Why my ticket was withdrawn?
Is this table wrong, or did I post something wrong in the other thread?
Just wondering about this ticket system which I don't understand yet..

[F.O.Bean]

its silly, they go up and down constantly, dont worry about the tickets

more info on them can be found in the archive section of ts.com

[inside source]

alright, thanks, sorry about this silly question.. 

[Genghis Cougar Mellen Khan]

I assumed that MD has 20 kOhm line input impedance, please correct me if I'm wrong. Is it correct for the new Hi-MD recorders? I didn't find it in the manual.

Why would you assume that?  I'd guess that it's 47k Ohm like previous recorders.  Does anyone know for fact what the line/mic impedence for the new Sony Hi-MD recorders is?

[audBall]

Mic-in frequencies (based on the pcm-m1 Mic-In resistance of 4.7 kOhm) :
  (16Hz) >  32Hz    2,3,4   
  (69Hz) > 138Hz   1,4   
  (95Hz) > 190Hz   1,3   
(107Hz) > 214Hz   1,3,4   
(160Hz) > 320Hz   1,2   
(195Hz) > 390Hz   1,2,4   
(888Hz) > 1776Hz 1,2,3   

Line-in frequencies (based on the pcm-m1 Line-In resistance of 47 kOhm) :
(16Hz) > 3.2Hz    2,3,4   
(69Hz) > 13.8Hz  1,4   
(95Hz) > 19Hz  1,3   
(107Hz) > 21.4Hz  1,3,4   
(160Hz) > 32Hz  1,2   
(195Hz) > 39Hz  1,2,4   
(888Hz) > 177.6Hz  1,2,3

Also valid for the d7 (or any other unit with a line-in resistance of 47 kOhm)

Could I make this same assumption with the JB3 (that going Mic-In would be a 10-fold increase in bass roll-off at the default db setting that mic-in provides??...i can't remember what that is right now). 

[dklein]

no, you'd have to measure it...but it doesn't really matter because the mic-in severely rolls off the high frequencies, rendering it useless for music recording.

[audBall]

no, you'd have to measure it...but it doesn't really matter because the mic-in severely rolls off the high frequencies, rendering it useless for music recording.

Thanks for the note...now I can definitely see why the roll-off option on the batt box is pointless for the JB3.  Looks like my switches won't get used now 

Although, could it be useful in conjunction w/ the AD20 (rolling off bass and increasing gain) effectively?  I'm planning on catching a hiphop show(Digable Planets) this weekend and would like to get somewhat of an idea of how to do this with the most desirable results.  Also, Kottke/Gordon is a couple days after.  Any suggestions?  I do have the phantom option, but I do not want to stealth with it.  Both shows are at the same venue and I don't think I could get the phantom in anyways (they pat you down, make you lift your belt area, etc...BS)

[inside source]

I assumed that MD has 20 kOhm line input impedance, please correct me if I'm wrong. Is it correct for the new Hi-MD recorders? I didn't find it in the manual.

Why would you assume that?  I'd guess that it's 47k Ohm like previous recorders.  Does anyone know for fact what the line/mic impedence for the new Sony Hi-MD recorders is?

As I stated I'm not sure. My assumption is based on what I found at minidisc.org forums - 20 kOhm impedance for line-in for both MD and Hi-MD models. I've seen 47 kOhm was also mentioned somewhere else in the internet. It would be great if someone could measure it and give us a definite answer. Unfortunately this characteristic is not listed in the minidisc manuals under specifications.


Also on this subject, below is a quote from someone at minidisc.org forums posted a while ago. It is contrary to all the posts here and I had asked for further clarification, but didn't get the answer. So what do you guys think?

- - -
Input impedance does not have any effect on the actual cut-off frequency of a filter. Fact is, only the filter itself is based on an impedance that bears an effect on the frequency being fed through it.

In the case of the input impedance of the recording device, the last thing we want is for the input to function as a filter as well and so by design, the impedance does not have an effect on the unit's intended frequency response hence the reason why mismatched impedances do not affect frequency response directly.

In theory, the input of an operational amplifier has infinite impedance to prevent loading of the output device feeding it the input signal whilst the output is of zero impedance to ensure maximum power is fed out of it. So it is this operational amplifier and its resistors which contribute to its overall input impedance - not a network of caps and inductors (as caps would be used for DC blocking purposes but nothing more).

What does affect mismatched impedances, however, is the maximum power transfer which affects the entire frequency spectrum as we're now talking about an amplitude related phenomenon.

So irrespective of what the bass roll-off filter's characteristics, whatever properly designed input it is plugged into, the characteristics of the filter remain the same leaving only its overall output power transfer affected.
- - -

[cgrooves]

Interesting quote to say the least.  As you stated, it is contrary to what has been stated here.  My knowledge is limited, however, I have discussed this issue with 2 different individuals that build battery boxes.  Both of these individuals informed me that their boxes were designed 'based on a generic impedance of 10 KOhms'.  Both of these individuals also stated that I would need to correlate the actual roll-off values, as based on the input impedence of the recording device used.

Most of our recording devices (if not all) do not utilize the 'generic impedance of 10 KOhms'. 
Like I stated above, this is only what I have been told by people I believed to be knowledgable about the subject. 

[dklein]

Poppycock!  First off, is this guy talking about passive filters?  It's not that the input impedance of the recording device is acting as a filter.  The DC blocking caps used in the battery box are effectively 'too small', which causes the desired rolloff.  The input impedance becomes the 'R' part of the RC circuit.  While an opamp has theoretical infinite input impedance, that's not what you get when you build a preamp circuit with it.

Clearly this person has some technical knowledge - perhaps they didn't understand the specific application.

Or maybe I don't know what I'm talking about...but then there's that real world experience...I've played with these circuits, different recorders, different cap values.  Maybe I'm not explaining it properly but it's not theoretical!  And this RC stuff is pretty basic electronics (not to say it's simple but you run into it everywhere if you're trying to learn the basics like I am).  Google it!

[inside source]

yeah, dklein, the application of this theary to this specific situation is exactly what I was questioning the original poster at minidisc.org.
Here is that thread: http://forums.minidisc.org/index.php?showtopic=9095  - the quoted post is #14.

Meanwhile, does "bass roll-off at 100 Hz" mean that the signal starts to decay at 100 Hz linearly and the signal amplitude is reduced by 6 dB at 50 Hz?

[inside source]

Both of these individuals informed me that their boxes were designed 'based on a generic impedance of 10 KOhms'.  Both of these individuals also stated that I would need to correlate the actual roll-off values, as based on the input impedence of the recording device used.

In this case the available bass roll-off settings on SP battery box make me wonder why they didn't include higher frequencies roll-off (between 195 and 888, so it could be used with DAT/HDD recorders which have up to 3-5 times higher input impedance. Or at least some kind of switch that would adjust for a higher input impedance.

Oh by the way I totally forgot about the formula for bass roll off calculation from the well-known Giant Squid FAQ from which I learned about the bass roll off in the first place. I think I should quote that one here as well for for completeness sake:

- - -

Q:  What is "bass roll off?"
 
A:  Bass Roll Off simply decreases the volume of the bass by using two capacitors within the circuitry.

Decreasing the bass can result in a better balance of highs and lows during playback if field recording is made in loud, big, boomy bass environments.

Bass roll off does not eliminate or cut off the low frequencies. 
 
Different input impediances of different models of recorders will give different roll off.
Here is a mathematical formula for figuring out what kind of roll you will get with different capacitors.

1/(6.28318 x Farad of the capacitor x Ohm of the recorder's input) = starting point of roll off.

The capacitors we use are .068 micorfarad.

Unlike some of our competitors we use the larger, higher quality Polypropylene Capacitors in our battery boxes that are designed for audio low frequency bypass.  As a result Giant Squid battery boxes delivers smoother roll off and low distortion.

- - -


ok, now finally using this formula I get 234 Hz as the starting point of roll off for 10 kOhm recorders's input, which is about 50 Hz for 47 kOhm. For Giant Squid battery box, of course.

[dklein]

Meanwhile, does "bass roll-off at 100 Hz" mean that the signal starts to decay at 100 Hz linearly and the signal amplitude is reduced by 6 dB at 50 Hz?

It's the -3dB point.  See the attached

[inside source]

Thanks a lot, dklein!
That were my doubts. So in fact it's -3 dB point and the decay starts much earlier. Looks like for "bass roll off at 100 Hz" we have about -1 dB at 200 Hz already.

[leegeddy]

Thanks a lot, dklein!
That were my doubts. So in fact it's -3 dB point and the decay starts much earlier. Looks like for "bass roll off at 100 Hz" we have about -1 dB at 200 Hz already.

.....but in practicality, can you REALLY distinguish a 1dB drop at 200hz in a recording given an already noisy environment?

to add to the discussion about rolloff filters, you could always design a higher order filter (say...12dB/octave or 18dB/octave) which will give you a sharper rolloff. that would involve using an RLC circuit.

marc

[inside source]

What about Edirol R-1? It has 100 kOhm line-in impedance. Is anyone using "bass roll-off at 888 Hz" (read 88.8 Hz) with it?