Jump to content

New from Rycote: Looks interesting


Eric Toline

Recommended Posts

The aural sensitivity curve tells us that our ears are very insensitive at LF (and totally so in the infrasonic range). No matter how good the monitoring is - and most speakers and headphones cannot handle <50Hz with any fidelity, we rarely hear much of the wind and handling noise spectrum (which is real bottom-end stuff) unless the levels are close peak.

Many of the "rumble" problems that one gets turn out to be short term overloads, where the amplifier chain has been pushed into momentary limiting. That's a wideband effect, since a saturated amp can't respond to any frequencies, even though it is caused by (inaudible) edge-of-band signals.

Modern transformerless-coupled microphones are often capable of generating staggering voltage outputs at extreme LF - no wonder that many amp chains grunt under the impact.

Chris Woolf

Link to comment
Share on other sites

  • Replies 80
  • Created
  • Last Reply

Top Posters In This Topic

I need to figure out where to put this in my wireless boom setup. We *mostly* use a Loon boom with their excellent 90degree connector. That low profile connector is really helpful indoors for ceiling issues.

8040 - LoonBoom - coiled XLR - MM1

Maybe: boom pole -> coiled XLR -> Tac!T -> MM1

I think the sooner I cut out the garbage, the better (meaning before my MM-1 and Lectro transmitter).

Link to comment
Share on other sites

Introduced noise (22Hz -22kHz) - 1.5dB

This interested me. I know that all electronics introduce noise to some degree, but hadn't really thought about how much. I tried searching on this for other low-cut filters but couldn't find anything. Is this a typical value? Also, just to clarify, does it mean that it has a noise floor of 1,5dB (therefore practically unnoticable compared to the self-noise of the mic), or that it adds 1,5dB to the existing noise floor?

Front-end filters on mixers are usually 6 or 12dB/octave, and these give a greater loss of wanted higher frequencies for a given cut of infrasonic or extreme LF noise.

What does this mean? That many low-cuts on mixers affect higher frequencies that they shouldn't, or that the knee might start a bit too high?

Also, does it introduce any noticable delay or otherwise affect the phase?

Link to comment
Share on other sites

"....does it mean that it has a noise floor of 1,5dB (therefore practically unnoticable compared to the self-noise of the mic), or that it adds 1,5dB to the existing noise floor?"

The 1.5dB is introduced noise - additional to what was there without it. Since the circuitry of the filter is active that is pretty well inevitable. I doubt that it would be apparent under the practical conditions that would require the use of the Tac!T.

[Front-end filters on mixers are usually 6 or 12dB/octave...] "What does this mean? That many low-cuts on mixers affect higher frequencies that they shouldn't, or that the knee might start a bit too high?"

Either of those statements could be true. What you are aiming to do with an HPF is to suppress the extreme LF and infrasonic by 30-40dB but retain as much of the interesting bass as possible. A shallow 6dB or 12dB slope from 60Hz will only give 12 or 24dB suppression at 15Hz (in theoretical terms), so you must either live with less LF suppression, or lift the knee frequency higher to give good suppression but accept greater loss of wanted frequencies.

Passive filters at the front of a mixer can only be first or second order. Active ones are needed for a steeper slope. Many LF filters on microphones are intended for proximity effect compensation and have a 6dB/oct slope for that.

Chris Woolf

Link to comment
Share on other sites

The 1.5dB is introduced noise - additional to what was there without it. Since the circuitry of the filter is active that is pretty well inevitable. I doubt that it would be apparent under the practical conditions that would require the use of the Tac!T.

I thought so. As you say it's not likely to be noticable, but it's good to know.

Thanks for the clarifications!

Link to comment
Share on other sites

  • 2 months later...
  • 3 months later...

Hello,

I 've used the Tac!T for 2 month now but for me, there is a major problem : cellphone interferences!!! I'm a doco sound mixer so I don't work in controlled environments. I can't ask to switch off all the phones. This happened when the phone is searching for cellular network.It happens maybe 10 times in 2 month but I don't like to work with the stress of this sort of problem happens during an important take. So for the moment, I remove it from my kit. Except that problem, it is a fantastic tool. Very efficient. I have contacted Rycote via my local dealer. I'm waiting for a good solution. Maybe, why not, using Neutrik EMC XLR. Or putting the circuitry in a small shielded box. Not so smart than in the XLR but if it could help.

Link to comment
Share on other sites

Hello,

I 've used the Tac!T for 2 month now but for me, there is a major problem : cellphone interferences!!! I'm a doco sound mixer so I don't work in controlled environments. I can't ask to switch off all the phones. This happened when the phone is searching for cellular network.It happens maybe 10 times in 2 month but I don't like to work with the stress of this sort of problem happens during an important take. So for the moment, I remove it from my kit. Except that problem, it is a fantastic tool. Very efficient. I have contacted Rycote via my local dealer. I'm waiting for a good solution. Maybe, why not, using Neutrik EMC XLR. Or putting the circuitry in a small shielded box. Not so smart than in the XLR but if it could help.

That's a pain. I suggested to Rycote long ago that it would be good to put the tac!t circuitry inside a connbox. They said they would consider it. It would be easy/easier to shield it, too.

Link to comment
Share on other sites

Interesting, thanks for your report from the field Olphi.. I havnt got one of these yet but seems like its the perfect match to the sennheiser 8000 series.. I hope that Rycote will be able to improve shielding somehow and let us know.. I also do mostly doc work and dont like unexpected signals coming through the headphones when we cant cut and do things again

Link to comment
Share on other sites

would a metal XLR MF barrel (two neutrik connectors back to back with the tacit pcb inside) provide adequate EMI/RFI shielding? there is a metal threaded sleeve that connects both the Male and Female Neutrik connectors - this is the current config of the Tacit - i got one from Rycote just two weeks ago. Earlier the XLRs had a cable in between with the pcb inside the male XLR.

Link to comment
Share on other sites

EMC and interference on mic circuits is a very difficult problem to deal with and there is rarely a single "weak" element that can be cured. You have to consider the microphone output impedances, the cable and connector balance and screening, and the load preamp impedances. Note the plural - the input leg-to-leg impedance and the legs-to-ground impedances are both relevant. And these have to be considered not only at audio frequencies but also at RF if the equipment doesn't exclude RF adequately.

Generally speaking mic circuits rely on balance - identical impedance to ground from each leg - to exclude interference, together with a low source impedance. At radio frequncies balance is virtually impossible to achieve so mic circuits should dump any induced RF voltage to the cable or equipment shield. Shielding ~can~ be important too but this is sometimes confused in location work by the fact that most "butt plug" radio TXs actually use the cable screen as an antenna. As an example of just how tricky things can be Rycote had a report of one combination of TX, Connbox and mic that often suffered interference - but changing ~any~ of those items cured it.

The Tac!T uses circuitry that is inherently balanced - it is a truly symmetrical arrangement - and also has components on the input and output to dump RF to Pin 1. However these components inevitably form part of a potential divider network with the mic circuitry and also the load preamp - so they cannot be independent of the electronic performance of these.

XLR connectors and barrels are not always screened. There was a convention of connecting shells to Pin 1 but the AES now recommends that this is avoided - it can cause as much interference as it was believed to reduce. Concatenated cabling always risks some unscreened shells, but if the input circuitry excludes RF effectively this shouldn't be a problem. On early Tac!Ts the shell ~was~ connected to the shell but it may well be that this is actually creating an interference problem in particular instances - though in design and testing I never came across it.

There are undoubtedly some mixer and TX inputs that do not have respectable CMRR (the measure of balance) or the ability to effectively reject RF and connecting ~anything~ to them can result in interference which will be blamed on the external equipment when the fault actually lies elsewhere. Dealing with that is very hard!

Rycote knows of a few incidences of interference that occur with both passive devices such as the Connbox, and a very few with the Tac!T but these tend to be very specific to the mic and preamp combination. We are investigating them and it should be possible to work out eventually where the interference is being injected and where it can be dumped to.

The Neutrik EMC connector is a splendid device but I couldn't fit a Tac!T board inside it - there's no room. And if one did it might well not be any better. The EMC connector only has value for diverting RF in the cable shield towards the cable shell and equipment casing. It is a a fine piece of engineering but not a magic bullet. It also cannot be used directly with some TXs because the internal ferrite on pin 1 is likely to severely limit the range by reducing the antenna length.

I ~would~ like to know of specific instances of interference occuring with the Tac!T (or Connboxes), ideally with detials of mic, mixer/TX and, if possible, a picture of the rig so that the number of intermediate connectors, cable lengths etc can be seen. I know a few mic and radio TX manufacturers who would love to share that information too - it is a headache to all of us!

Chris Woolf (with a Rycote hat on)

Link to comment
Share on other sites

Hello Chris,

this is my actual setting. Schoeps CCM- 5 meters XLR to XLR canare starquad cable - Tac!T- Sounddevices 552 and now 664. When I remove the Tac!T, I don't have any problems .I work with the 552 since 3 years with the same set up (without the Tac!T) and I never have any problems. I have tried to loose the XLR body from the shield of the cable but without any good result. I some have problems when i put my cell phone searching a network close to the Tac!T (It also happened in a small room with no cell phone close to me but somewhere in the room). Once again, the Tac!T is really a great value for my work and I m very disappointed to not able to use it every day.

Best regards.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


×
×
  • Create New...