Mar 162012
 

When I added the cube to the studio I was originally thinking that it would be just a handy practice amp for Chaos. He was starting to take his electric guitar work seriously and needed an amp he could occasionally drag to class.

Then the day came that one of our guitar friends showed up to record a session for ALT-230 and had forgotten their amp. So, instead of letting the time slot go to waste we decided to give the little cube a try. We figured that if what we got wasn’t usable we would re-amp the work later or run it through Guitar Rig on the DAW.

We were very pleasantly surprised! The tracks were so good they survived all the way through post production. Ever since then we’ve been hooked. We’ve been using the Cube regularly now any time we want to do some relatively clean electric guitar work and we’ve been getting consistently good results.

The normal setup for this involves a R0DE NT2-a paired with a Shure SM57, both set about 30 degrees off axis, about half a meter away, close together and in phase (diaphragms abeam). Some times we give them a little separation from each other  if we want more “space” in the stereo image. Anything from 5 to 20 cm usually works ok.

Then for good measure we’ll run the guitar through a direct box on it’s way in just in case we want to re-amp it later. This too has become a fairly standard procedure no matter what amp we’re using.

Usually when I’m setting up like this I will put the two mics on separate channels through the Furman monitor rig so I can hear them in the headphones separately and summed on demand. That makes it easy to move things around to fine tune mic positioning and any other tweaking that might be needed.

Today we had yet another successful session with the rugged, versatile little cube; and right after that Chaos plugged in to practice his guitar lessons. I couldn’t help but grin at being reminded how far this little practice amp had come. If you don’t have one yet you probably need it and don’t know it!

Nov 212010
 

Often church sound folk are looking for the cheapest possible solution for recording their services. In this case, they want to use a low-end voice recorder and record directly from the mixing board.

There are a number of challenges with this. For one, the voice recorder has no Line input – it only has a Mic-input. Another challenge is the AGC on the recorder which has a tendency to crank the gain way up when nobody is speaking and then crank it way down when they do speak.

On the first day they presented this “challenge” they simply walked up (at the last minute) and said: “Hey, plug this into the board. The guys at Radio Shack said this is the right cable for it…”

The “right cable” in this case was an typical VCR A/V cable with RCA connectors on both ends. On one end there was a dongle to go from the RCA to the 1/8th inch stereo plug. The video part of the cable was not used. The idea was to connect the audio RCA connectors to the tape-out on the mixer and plug the 1/8th inch end of things into the Mic input on the voice recorder.

This by itself was not going to work because the line level output from the mixer would completely overwhelm the voice recorder’s mic input– but being unwilling to just give up, I found a pair of RCA-1/4 inch adapters and plugged the RCA end of the cable into a pair of SUB channels on the mixer (in this case 3 & 4). Then I used the sub channel faders to drop the line signal down to something that wouldn’t overwhelm the voice recorder. After a minute or two of experimenting (all the time I had really) we settled on a setting of about -50db. That’s just about all the way off.

This worked, sort of, but there were a couple of problems with it.

For one, the signal to noise ratio was just plain awful! When the AGC (Automatic Gain Control) in the voice recorder cranks up during quiet passages it records all of the noise from the board plus anything else it can get it’s hands on from the room (even past the gates and expanders!).

The second problem was that the fader control down at -50 was very touchy. Just a tiny nudge was enough to send the signal over the top and completely overload the little voice recorder again. A nudge the other way and all you could get was noise from the board!

(Side note: I want to point out that this is a relatively new Mackie board and that it does not have a noise problem! In fact the noise floor on the board is very good. However the voice recorder thinks it’s trying to pick up whispers from a quiet room and so it maxes out it’s gain in the process. During silent passages there is no signal to record, so all we can give to the little voice recorder is noise floor — it takes that and adds about 30db to it (I’m guessing) and that’s what goes onto it’s recording.)

While this was reportedly a _HUGE_ improvement over what they had been doing, I wasn’t happy with it at all. So, true to form, I set about fixing it.

The problem boils down to matching the pro line level output from the mixer to the consumer mic input of the voice recorder.

The line out of the mixer is expecting to see a high input impedance while providing a fairly high voltage signal. The output stage of the mixer itself has a fairly low impedance. This is common with today’s equipment — matching a low impedance (relatively high power) output to one (or more) high impedance (low power, or “bridging”) input(s). This methodology provides the ability to “plug anything into anything” without really worrying too much about it. The Hi-z inputs are almost completely un-noticed by the Low-z outputs so everything stays pretty well isolated and the noise floor stays nice and low… but I digress…

On the other end we have the consumer grade mic input. Most likely it’s biased a bit to provide some power for a condenser mic, and it’s probably expecting something like a 500-2500 ohm impedance. It’s also expecting a very low level signal – that’s why connecting the line level Tape-Out from the mixer directly into the Mic-Input completely overwhelmed the little voice recorder.

So, we need a high impedance on one one end to take a high level line signal and a low impedance on the other end to provide a low level (looks like a mic) signal.

We need an L-Pad !

As it turns out, this is a simple thing to make. Essentially an L-Pad is a simple voltage divider network made of a couple of resistors. The input goes to the top of the network where it sees both resistors in series and a very high impedance. The output is taken from the second resistor which is relatively small and so it represents a low impedance. Along the way, the voltage drops significantly so that the output is much lower than the input.

Another nifty thing we get from this setup is that any low-level noise that’s generated at the mixer is also attenuated in the L-Pad… so much so that whatever is left of it is essentially “shorted out” by the low impedance end of the L-Pad. That will leave the little voice recorder with a clean signal to process. Any noise that shows up when it cranks up it’s AGC will be noise it makes itself.

(Side note: Consider that the noise floor on the mixer output is probably at least 60 db down from a nominal signal (at 0 db). Subtract another 52 db from that and the noise floor from that source should be -112 db! If the voice recorder manages to scrape noise out of that then most of it will come from it’s own preamp etc…)

We made a quick trip to Radio Shack to see what we could get.

To start with we picked up an RCA to 1/8th inch cable. The idea was to cut the cable in the middle and add the L-Pad in line. This allows us to be clear about the direction of signal flow– the mixer goes on the RCA end and the voice recorder goes on the 1/8th inch end. An L-Pad is directional! We must have the input on the one side and the output on the other side. Reverse it and things get worse, not better.

After that we picked up a few resisters. A good way to make a 50db L-Pad is with a 33K Ω resistor for the input and a 100 Ω resistor for the output. These parts are readily available, but I opted to go a slightly different route and use a 220K Ω resistor for the input and a 560 Ω resistor for the output.

There are a couple of reasons for this:

Firstly, a 33K Ω impedance is ok, but not great as far as a “bridging” input goes so to optimize isolation I wanted something higher.

Secondly, the voice recorder is battery powered and tiny. If it’s trying to bias a 100 Ω load to provide power it’s going to use up it’s battery much faster than it will if the input impedance is 560 Ω. Also 560 Ω is very likely right on the low end of the impedance of the voice recorder’s input so it should be a good match. It’s also still low enough to “short out” most of the noise that might show up on that end of things for all intents and purposes.

Ultimately I had to pick from the parts they had in the bin so my choices were limited.

Finally I picked up some heat-shrink tubing so that I could build all of this in-line and avoid any chunky boxes or other craziness.

Here’s how we put it all together:

1. Heat up the old soldering iron and wet the sponge. I mean old too! I’ve had this soldering iron (and sponge) for close to 30 years now! Amazing how long these things last if you take care of them. The trick seems to be – keep your tip clean. A tiny sponge & a saucer of water are all it takes.

2. Cut the cable near the RCA end after pulling it apart a bit to provide room to work. Set the RCA ends aside for now and work with the 1/8th in ends. Add some short lengths of appropriately colored heat-shrink tubing and strip a few cm of outer insulation off of each cable. These cables are CHEAP, so very carefully use a razor knife to nick the insulation. Then bend it open and work your way through it so that you don’t nick the shield braid inside. This takes a bit of finesse so don’t be upset if you have to start over once or twice to get the hang of it. (Be sure to start with enough cable length!)

3. Twist the shield braid into a stranded wire and strip about 1 cm of insulation away from the inner conductor.

4. Place a 560 Ω resistor along side of the inner conductor. Twist the inner conductor around one lead of the resistor, then twist the shield braid around the other end of the resistor. Then solder these connections in place. Use caution — the insulation in these cables is very sensitive to heat. Apply the tip of your soldering iron to the joint as far away from the cable as possible and then sweat the solder toward the cable from there. This allows you to get a good joint without melting the insulation. Do this for both leads.

5. The 560 Ω resistors are now across the output side of our L-Pad cable. Now we will add the 220K Ω series resistors. In order to do this in-line and make a strong joint we’re going to use an old “western-union” technique. This is the way they used to join telegraph cables back in the day – but we’re going to adapt it to the small scale for this project. To start, cross the two resistor’s leads so that they touch about 4mm from the body of each resistor.

6. Holding the crossing point, 220K Ω resistor, and 560 Ω lead in your right hand, wind the 220K Ω lead tightly around the 560 Ω lead toward the body of the resistor and over top of the soldered connection.

7. Holding the 560 Ω resistor and cable, wind the 560 Ω resistor’s lead tightly around the 220K Ω resistor’s lead toward the body of the resistor.

8. Solder the joint being careful to avoid melting the insulation of the cable. Apply the tip of your soldering iron to the part of the joint that is farthest from the inner conductor and sweat the solder through the joint.

9. Clip of the excess resistor leads, then slide the heat-shrink tubing over the assembly toward the end.

10. Slide the inner tubing back over the assembly until the entire assembly is covered. The tubing should just cover 1-2 mm of the outer jacket of the cable and should just about cover the resistors. The resistor lead that is connected to the shield braid is a ground lead. Bend it at a right angle from the cable so that it makes a physical stop for the heat-shrink tubing to rest against. This will hold it in place while you shrink the tubing.

11. Grab your hair drier (or heat gun if you have one) and shrink the tubing. You should end up with a nice tight fit.

12. Grab the RCA end of the cable and lay it against the finished assembly. Red for red, and white for white. You will be stripping away the outer jacket approximately 1 cm out from the end of the heat-shrink tubing. This will give you a good amount of clean wire to work with without making the assembly too long.

13. After stripping away the outer jacket from the RCA side and prepping the shield braid as we did before, strip away all but about 5mm of the insulation from the inner conductor. Then slide a length of appropriately colored heat shrink tubing over each. Get a larger diameter piece of heat-shrink tubing and slide it over the 1/8 in plug end of the cable. Be sure to pick a piece with a large enough diameter to eventually fit over both resistor assemblies and seal the entire cable. (Leave a little more room than you think you need.)

14. Cross the inner conductor of the RCA side with the resistor lead of the 1/8th in side as close to the resistor and inner conductor insulation as possible. Then wind the inner conductor around the resistor lead tightly. Finaly, solder the joint in the usual way by applying the tip of your soldering iron as far from the cable as possible to avoid melting the insulation.

15. Bend the new solder joints down flat against the resister assemblies and clip off any excess resistor lead.

16. Slide the colored heat-shrink tubing down over the new joints so that it covers part of the resistor assembly and part of the outer jacket of the RCA cable ends. Bend the shield braid leads out at right angles as we did before to hold the heat-shrink tubing in place. Then go heat them up.

17. Now we’re going to connect the shield braids and build a shield for the entire assembly. This is important because these are unbalanced cables. Normally the shield braids provide a continuous electrical shield against interference. Since we’ve stripped that away and added components we need to replace it. We’ll start by making a good connection between the existing shield braids and then we’ll build a new shield to cover the whole assembly. Strip about 20 cm of insulation away from some stranded hookup wire and connect one end of it to the shield braid on one end of the L-Pad assembly. Lay the rest along the assembly for later.

18. Connect the remaining shield braids to the bare hookup wire by winding them tightly. Keep the connections as neat as possible and laid flat across the resistor assembly.

19. Solder the shield connections in place taking care not to melt the insulation as before.

20. Cut a strip of ordinary aluminum foil about half a meter long and about 4 cm wide. This will become our new shield. It will be connected to the shields in the cable by the bare hookup wire we’ve used to connect them together.

21. Starting at the end of the assembly away from the shield lead, wind a layer of foil around the assembly toward the shield lead. On each end of the assembly you want to cover about 5-10 mm of the existing cable so that the new shield overlaps the shield in the cable. When you reach that point on the end with the shield lead, fold the shield lead back over the assembly and the first layer of foil. Then, continue winding the foil around the assembly so that you make a second layer back toward where you started.

22. Continue winding the shield in this way back and forth until you run out of foil. Do this as neatly and tightly as possible so that the final assembly is compact and relatively smooth. You should end up with about 3-5 layers of foil with the shield lead between each layer. Finally, solder the shield lead to itself on each end of the shield and to the foil itself if possible.

23. Clip off any excess shield lead. Then push (DO NOT PULL) the large heat-shrink tubing over the assembly. This may take a little time and effort, especially if the heat-shrink tubing is a little narrow. It took me a few minutes of pushing and massaging, but I was able to get the final piece of heat-shrink tubing over the shield assembly. It should cover about an additional 1 cm of cable on each end. Heat it up with your hair drier (or heat gun if you have it) and you’re done!

24. If you really want to you can do a final check with an ohm meter to see that you haven’t shorted anything or pulled a connection apart. If your assembly process looked like my pictures then you should be in good shape.

RCA tip to RCA tip should measure about 441K Ω (I got 436K).

RCA sleve to RCA ring should measure 0 Ω. (Shields are common).

RCA tip to RCA ring (same cable) should measure 220.5KΩ (I got 218.2K).

RCA sleve to 1/8th in sleve should measure 0 Ω.

RCA Red tip to 1/8th in tip should be about 220K Ω.

RCA Red tip to 1/8th in ring should be about 1K Ω more than that.

Mar 232010
 

The Direct Sound EX-29, extreme isolation headphones absolutely live up to the hype. Bleed is non-existent; they are comfortable; they are clear; and they are very quiet. I’ve been using these in the studio for a few days now and I don’t know how I ever lived without them. Really- they are that good!

I try to spend a good deal of time behind the kit if I can swing it – just for fun, but also working out drum tracks for new songs, and of course, recording new material. These headphones shine in all of these applications.

Just Jammin’:

When I’m just jammin’ and keeping my chops up these cans help me keep everything at a sane volume which means I can work longer without fatigue and without damaging my hearing. In the past I have used ear plugs of various types and they have all had a few critical drawbacks that the EX-29s don’t. Two that spring to mind are comfort and clarity.

[ What do you mean “clarity”… ear protection isn’t supposed to be clear anyway! ] I MEAN- ear plugs aren’t clear – ever! At least not in my experience. Nor are most other practical solutions.

If you’ve spent any serious time (multi-hour sessions) behind the kit with ear plugs you know what I’m talking about — You can’t hear what you’re doing and it really takes a toll on your subtlety. Most likely you got frustrated at some point and flicked the ear plugs across the room so you could hear again. (You did have them in at first didn’t you??!)

The EX-29s surprisingly don’t have this problem. One of the first things I noticed was how flat the attenuation was. After a few minutes in the relative quiet of the EX-29s I adapted and was able to hear everything – just at a lower level. This means I don’t lose crush rolls, ghost strokes, and cymbal shading for the sake of my hearing. Don’t get me wrong — it’s not perfect 🙂 but it is worlds better than any ear plugs I’ve ever used and the translation of subtlety has a big pay-off in that I don’t suffer any fatigue from trying too hard to hear what I’m doing.

Then there’s comfort. Of course phones of any kind are going to be more comfortable than plugs… but the EX-29s do better than that. They are truly comfortable even after more than a couple of hours. They don’t squeeze your head, and they lack that pillows-on-the-ears feeling that typically comes with good protection.

Writing:

When I’m working out new drum tracks I often spend hours trying things out. That means playing back scratch tracks, samples, and loops and playing along to find the right grooves and fills. I used to use my Sony MDR-V600s for this. I would try to keep things at a low level, or I might use a bit of cotton (if I thought of it)… but invariably things would eventually get out of control or I would get tired from fighting with it and would have to come back later.

The EX-29s have solved this problem for me. I don’t miss any of the clarity I get from my V600s AND I don’t need any cotton for the ears :-).

The first thing I noticed when I used the EX-29s was that I had to turn my Furman monitor system way down! (ok, 2-3 notches) Everything was still clear, and I could hear my playing along with the playback without struggling to adjust to unnatural muffling. Even better – I didn’t get frustrated with it and discard my protection!

Recording:

Recording sessions are where the EX-29s really come through. Once the mics are on and every sound matters there are several things that shine about the EX-29s. In no particular order:

The isolation is absolutely fantastic! I frequently play pieces that demand a lot of dynamic range (I’m an art-rock guy at heart). It’s surprising how sensitive the mics need to be when you want to capture the subtlety of such a loud instrument. Any bleed-through from the playback can destroy the subtlety of a quiet passage by forcing re-takes or necessitating the use of gating, expansion, and other trickery. It’s no wonder drums are so frequently sequenced these days– it boils down to time and effort (which means money).

The EX-29s truly solve the isolation problem in two ways. The attenuation of the shells is quite substantial but in addition to that the quality of the drivers is also fantastic! This combination means that you can achieve comfort and clarity at substantially reduced playback levels. Not only is your playback not likely to get into your mics, but it is also at a much lower level to begin with.

Do the math (I did) — you not only drop about 30db getting from the inside of the EX-29s to the outside; you also drop an additional 12-15db using lower levels in the first place. That’s 45db of effective isolation without struggling to adapt or building up fatigue trying to “hear it”. Compare that to what you’re doing now and chances are you’ll see a 20db advantage with the EX-29s – not to mention more comfortable and productive recording sessions.

I’ll admit it – When I first heard about the EX-29s I was more than a little skeptical. They just seemed too good to be true. When I finally broke down and ordered them it was with the attitude that I’d give them a shot and if (when) they didn’t quite cut it I would find some other use for them.

No longer – These EX-29s are the real deal. They have earned a permanent home in my studio. I’m glad I picked up the extra pair to hang on my book shelf so we won’t have to fight over who gets to use them 🙂

Feb 032010
 

Noise, Noise, Noise, Noise! grumbled the Grinch… and I feel his pain. One of the challenges of building a recording studio is noise. We live in a very noisy world.

One way we deal with noise is to put noisy things in a special room which can be isolated from the recording environment. Here at the Mad Lab we have a utility room where we keep our server farm, CD/DVD production robot, air-handler, and other noisy things. The trick is: How do we keep all that stuff quiet?

There are two things we want to do to this room: Reduce the noise inside the room as much as possible and then prevent whatever is left over from leaking out.

The first step to treating the room was to significantly increase the density of the walls. At the same time we wanted to increase the structural integrity of the paneling on the opposite side. What we did was to add a thick, dense layer of work-bench material to the outside of the wall directly behind the paneling (another story we’ll post later).

The next step was to add sound absorbing material to the inside of the room to absorb as much noise as possible (and convert it to heat). The thinking behind this is that the more sound we can absorb the less sound there is to bounce around the room and leak out.

In addition we decided to put physics to work for us and install this material so that it is suspended from the studs flush with the inside of the wall leaving an air gap between the insulation and the outer wall material. This accomplishes two things. The insulation on the inside surface  is mechanically isolated from the outer wall structure thus preventing any (most) mechanical sound transmission. Also the air gap represents an additional change in density so that any sound attempting to travel through the wall from the inside experiences at least three separate mediums (more on this in a moment).

We did some research and contacted our friends at Sweetwater to purchase some Auralex mineral fiber insulation. Then to make it easier to handle we had our friends at Silk Supply Company precision cut the material and manufacture fabric covered panels.

The custom made panels fit perfectly between the studs and leave a gap of about half an inch between them and the dense outside wall. When sound attempts to escape through the wall three things happen.

First a lot of the energy is absorbed into the mineral fibers — the fabric covering is acoustically transparent. This significantly reduces any echos inside the room and converts a good portion of the sound to heat. This effect is enhanced by the loose mechanical coupling of the installation. Since the panels are suspended from the front surface of the studs any mechanical energy that might be transmitted through the studs is first significantly attenuated as it travels through the mineral fibers to the edges.

Second, any sound that makes it through the  insulation escapes into the air gap where the change in density causes the sound to refract… well, sort of. The size of the gap is very small compared to the wavelength of most sounds so most of the effect is really a mechanical decoupling of the mineral fiber and the hard surface of the outer wall material.

Third, much of the sound in the air gap is reflected back toward the mineral fiber by the smooth, hard surface of the outer wall material. In addition the density of the material further attenuates whatever is not reflected.

Since one of my goals was to attenuate the noise inside the room (and for a number of other reasons) I didn’t want to go the more conventional route of adding thick layers of drywall.

In line with this, the fabric covering has a few additional benefits. To start with the installation is much easier to install and if need be it can be temporarily removed by pulling the staples and tugging the insulation out of it’s slot. This might be useful if I need to run any additional cabling, for example. In addition to that the fabric reinforces the mineral fiber and keeps it well contained so it doesn’t sluff off into the room over time.

As usual I enlisted Ian and Leo to perform the installation. They had a lot of fun exploring the change in acoustic properties by alternately talking in front of sections where they had installed the panels and sections where the panels were not yet installed.

Dec 172009
 
High-Def-Spelling

High-Def-Spelling

How does an 8 year old do his spelling homework when he has access to a high-definition digital studio?

By voice-over of course!

We hit upon this idea when it became clear to us that ordinary spelling homework is, well, ordinary. We can do better than this I thought — and off to the Mad Lab we went with spelling words in hand.

Now Ian not only gets his spelling right; he also gets to do something most people never experience… When is the last time you did a voice-over in a real recording studio?

Here’s how it works: First we set up a recording session with all the bells and whistles. Then Ian reads his spelling words as clearly as he can and leaves enough space in between each word so that he’ll have time to write the words down when we play it back. Then we play it back for him (hopefully without stopping) and he writes them down. This is much more exciting than having one of us read his words to him – and there are added benefits.

In addition to spelling he is learning about the way things work in a studio — especially the recording process. This covers a lot of additional skills and knowledge. There’s science (mic positioning, setting levels), planning and following a process, teamwork, communications skills (not just the voice-over itself, but the interaction between the engineer and the performer too), patience, etc. He also learns what every voice-over artist learns— there is no hiding from that microphone! The details matter and so as he progresses he’s learning to speak clearly, to avoid making unnecessary noises, and to pay attention to the details.

He’s also having a blast with it! And so am I.