Archive of the Ask Eddie Category
Wow! Winter break simultaneously went by all too fast and yet, it seems like forever ago that I was teaching analog recording, doing a Zed Lep cover for our penultimate class. On the final class, everyone was so burnt out by final exams that we played vinyl for THREE HOURS! (Gentle Giant’s KNOTS, Frank Zappa’s MOVIN’ TO MONTANA, The Robins’ SMOKEY JOE’s CAFE, Sinatra, Gene Vincent, Johnny Guitar Watson, Les Paul – it was quite the journey.)
That said, my brain is flying with zillions of ideas that must be well focused in time for my students’ first electronic experience – I don’t want to scare anyone off. To soften the landing, hands-on is heavily emphasized – starting with the familiar 9-volt battery to the tongue and then…
Learn how to use a Multi-meter, a piece of Test Equipment that, as the name implies, does multiple things – measure volts, current (in amps) and resistance (in ohms)…
After proving the 9-volt battery is worthy, it’s time to get hip to the solder-less breadboard. With a little experience, it can used to demo a simple stomp box circuit and just about any idea you can throw at and fit on it!
I said ‘hands-on,’ right? Seeing the images, touching all the parts, getting familiar enough to make the breadboard do your bidding is key. Students connect a battery, a Light Emitting Diode (LED) and a Resistor. When the LED lights up, it’s time to take a union cig break and pat yourself on the back..
With just this little bit of familiarity under our belts it’s time to delve into the schematic symbol codex – the visual language of electronic circuits…
We see the circuit as a physical entity, learn the schematic symbol for each component and then whip out the multimeter and take some measurements.
I’m off to do it for real, so L8R!
With the help of Chris Juried, whose father took this and many other pictures of New York City studios…
To visit this work in progress, click on the link below.
I have identified some of the equipment, but feel free to comment, especially if you can identify the mystery gear – console, white boxes over Pultecs (which Pultecs??), name of that style patch bay, pix of dual-pronged patch plugs, etc.
MiraSound NYC mid-to-late sixities
I teach, therefore I am constantly experimenting, so when students ask “How long have you been doing this or that,’ sometimes my reply is “I just tried it for the first time.”
Of course, we ALL rotate through the ‘known’ tricks until satisfied. Last week, a student walked in with TWO B&O ribbon mics and we immediately put them to good use. (The mics were borrowed from another instructor, Tom Garneau, the B&O design inspired Speiden and then Royer.)
For our control room rehearsal session we set up three mics about 5 feet from the drum kit. About 1 1/2 feet off the floor were the B&O ribbons on a Cascade T bar. Four feet directly above was an EV-664A hyper-cardioid to catch the top side of the kit.
You can hear the tracks in isolation at the link immediately below. Spoiler alert – the tracks were essentially solo’d from the mix so they have EQ and Compression.
0:00 – 0:42 = B&O
0:43 – 1:06 = EV 664a
1:07 – 1:29 = Live chamber + all three mics
1:30 – 2:08 = Bass DI (left) + Bass amp (right)
2:09 – end = other instruments added.
I have been favoring dynamic and ribbon mics as they tend to have less top end, better rejection and work well in ensemble sessions where rejection is useful.
If you want more space and no proximity effect the EV635A is great – on acoustic guitars, drums and even those guttural metal vocals. It’s still manufactured and @$119 street, is affordable.
NO FEAR OF REJECTION!
A pair of ribbon mics on a singing acoustic acoustic guitarist can deliver remarkable isolation, presence and warmth. I’ve had access to several ribbon mics, including the Royer, Reslo, RCA 44A and 74 Junior, Coles 4038 and Cascade. All are unique but only the Cascade models are within a student’s budget. I have a pair of Fatheads and a Vin Jet (RCA 44 ribbon style) in my classroom mic cabinet.
The cascade Fat Head (short ribbon) is $175 and is great on guitar amps – about 2 feet from the cab works pretty well. The VinJet (long ribbon) is a bit like the RCA 44. like all ribbons, they do not exaggerate the amplifier grit that brighter mics do.
This past week, my class used a stereo pair of Fatheads on the drums – as described above – along with the EV-664A (plus a Sennheiser shotgun to catch the room bounce). Here’s a mix of the session, mostly live, with fatheads on the lead and tremelo guitar ODs.
Student ‘Zed Lep’ Session Recording
Students should keep in mind that ribbons should not be ‘eaten’ by humans or drums (avoid extreme close-ups) because the ribbon is delicate. They also have low output, but you can get an external preamp / booster. One version is called the Cloud Lifter – available in mono and stereo versions.
CLOUD Ribbon Mic Helper
Another vintage fave is the EV-664 another ‘isolationist’ mic that’s good on vocals, kick and toms.
The bass amp on both of these recordings is an SWR LA-8 practice amp with either an EV RE-11 or a Shure SM-58 directly on the cab. The DI is via a JFET preamp with an optical limiter of my own design.
When capturing bass amp tone, I rely on proximity effect to do the heavy low-end lifting, tweaking the amp EQ a little bass shy so that the mic gets what I want. That plus getting the amp off the floor a helps alot with ‘de-stimulating’ the room and reducing leakage.
If you’re new to recording, please let me know if you find these tips helpful and feel free to share your own.
PS: My thanks to James Andrew Meadows (Drums), Dillon Marchus (Bass), Zach Johnson and Shaun Ortman (Guitars and Eng), Peter Vel and Jake Goodroad (Eng and Tape Op), Michael Freeman rogers (Vocals – although not featured in these mixes), John Kargol (Tech Support) and Stan Coutant for his awesome microphone site!
I teach an Analog Recording Class four times a year – five weeks of editing, flanging and 4-track plus five weeks of 24-track. While not trying to ‘sell’ the various analog tape formats – I embraced in-the-box mixing last century – I do ask my students to take a step back from the one-instrument-at-a time, pitch correction, beat detection, plug-in mania and consider recording a live rhythm track – no click, no headphones, just musicians listening to each other and ‘mixing themselves’ on the fly.
The goal is to transfer what was learned in the process back to the Digital Lo Mein. If they decide to buy a used tape machine, well, that’s icing on the cake! There is nothing like an emotion-modulated soaring flange rather than the oscillator driven version – hardware or plug-in – or rolling your own live chamber. And let’s face it, in this economy, for students trying to find their way, the minimalist approach works economically and emotionally – perhaps the ‘discerning listener’ will feel more connected and not quite understand why…
People Will Come, Ray!
We start with four track half-inch tape and a handful of preamps. I give them a little breathing room in that the target is one instrument / one microphone per track, UNLESS we take advantage of a two-input, one-output mixer-limiter (the Altec 1612) to combine Bass And Drums (one mic each) to one track of tape.
But first I show them this video – one cheap omni condenser mic on a drum kit – no EQ or dynamics processing. Just a good drummer, a decent sounding kit and an untreated space. My students call this the “Crotch Mic Technique!” Oh, and this microphone is working extra hard by driving six pre-amps at once.
BASS AMP ONLY
I once was a Bass DI + amp guy until one day when recording a rehearsal, I stumbled upon a trick that has worked ever since. David Trampe is the student bassist on this track. (For this session, we simultaneously recorded to analog and digital formats. This is the digital version.) David played my UNIVOX P-Bass copy through his SWR LA-10 amplifier. I chose what was available – an Shure SM-58. You can pretty much use anything, but I recommend the following.
- Bass cab off the floor to minimize boom-in-the-room
- 8-inch to 10-inch small-speaker cabs for a tight, controlled tone
- Start by EQ-ing the bass amp for a clear, tone (minimize the mud), less bassy than bassists would normally choose (this also applies to live)
- Use any directional mic as close to the speaker as possible to take advantage of proximity effect – this restores the warmth lost by the previous step, it also reduced mud and leakage in the performance area
- Almost any mic preamp and limiter (the latter gently kissing the peaks as needed)
- Once you get this far, tweak the amp EQ as necessary to get as close to the desired tone as possible.
FOUR TRACK FUN
Here are two songs we did in class. Four Rhythm tracks bounced to one leaving three tracks for overdubs.
PICTURES OF MATCHSTICK MEN
ME AND BOBBY McGEE
Live vocal, acoustic and lead guitar overdubbed.
EIGHT OF of 24-TRACKS
FIVE AGAIN (live)
24 TRACKS LIVE (no waiting)
IF YOU WANT ME TO STAY (live)
Many entry level converters only have two microphone inputs, which is fine when you’re working at home or doing live stereo recordings. But with ‘the right bit of clever’ you can convert line inputs to mic inputs with a simple adapter. Several years ago I did this with DigiDesign’s 002 (it has four mic and four line inputs). I currently own an M-Audio 1814 (2 mic inputs).
Inside the adapter shown is a Low Impedance (balanced) to High Impedance (unbalanced) matching transformer- nothing fancy – and likely to saturate with high-level sources – sometimes that’s the ‘color’ you want. Parts Express also has in-line adapters for polarity reverse and attenuators (pads) which are handy beyond this application. Every ‘audio emergency kit’ should have a few.
If you wanna pimp your converter, check out the ‘shiny transformer’ links. (PS: Requires, fine motor skills like metal shop, wire stripping and soldering.)
Shiny High-Performance Transformers
A BOX TO PUT IT IN
I’ve always enjoyed your writing! I’m not really that much of a tech, but I have a lot of old stuff (I mean vintage), and your MIX column gives me faith that I will be able to find someone who can repair my prized gear.
Today I wanted to repair a Pro Jr. input jack, and I am certain that once upon a time you had an article in Mix detailing your repair of one of these. I can’t find it on the web. I hope this isn’t too annoying, but, do you have that article stored anywhere?
Sorry to bug you, and thanks!
I have a Pro Junior that I’ve done some mods to, but I don’t recall anything about the jack. That said, this link below should help! Antique Electronic Supply is very tube amp friendly.
I was off on vacation for a week so there’s some catching up to do. For starters, I am going to post some links and, over time, come back and explain in more depth how these links can help you…
As mentioned, upgrading opamps in the audio path can a bit of a mine field. But not ALL opamps are in the signal path – the side-chain of vintage dbx compressor-limiters, for example, have opamps that do all sorts of fun stuff. So, when an opamp’s functionality is circuit-critical, check the manufacturer’s website first, because sometimes you can get lucky and find a compatible replacement.
As the link shows, the LM308 has been DISCONTINUED, but to the right is a link to the LM308 DATASHEET as well as it’s replacement – in the ALSO RECOMMENDED box – the LM8261. You’ll want to download the datasheet for both parts…
Power Supplies are often the weak link in many products, not necessarily by circuit design so much as the lack of consideration of how heat shortens life over long periods of time. In general, electronics components should not be so hot as to burn, but ‘too hot to fail’ happens all too often, especially when you consider how often rack gear is mounted with no space in between. Over time, parts just burn themselves out.
RECTIFIERS Convert AC to DC and there are many types, from Half Wave to Full Wave, Single Voltage to Bipolar as well as Voltage Doubler.
Can You NAME THAT RECTIFIER?
Once AC is converted to DC it needs to be regulated – it must tolerate variations at the power outlet – it can’t sag when the Air Conditioner or Heater comes on and must be there if the device being powered demands more juice.
Theses days, pretty much every solution comes as a single Integrated Circuit or IC, with a minimal amount of support parts. But if you work on vintage Gear, you’ll see many Variations on the Regulation Theme.
If you ever wanted to know more about regulated power supplies, National Semiconductor published this useful FUNDAMENTALS pdf.
Back in the vacuum tube daze, capacitors were big enough to tell you alot about themselves. Then, large and small value caps relied on color code. Now reading and translating much small conventional (axial or radial) capacitors can be confusing, because limited space forces manufacturers to abbreviate. It’s even crazier with surface mount (SMT) parts. I’ll be posting a chart soon, but in the meantime, here’s a cool link that explains alot about what some of the abbreviations mean. Note that some of these abbreviations might be on the schematic as well.
more to come…
Q: Why don’t PC mics don’t work on a standard console?
This remarkably common question most recently came from Andreas Polydoros from Athens, Greece.
A: Because there is a big difference between a conventional phantom-powered studio mic and the Electret microphones typically found in computers, cell phones, cameras and portable recording devices. The Electret condenser mic does require power (for its built-in amplifier) but in a totally different way from the Phantom-powered studio condenser mics that have been part of our audio-centric world since the sixties.
My first ‘phantom’ article originally appeared in the July 1999 issue of EQ.
In mic evolution, moving coil and ribbon mics deliver a balanced / differential signal by design and required no power. Initially, studio condenser microphones required power to polarize the capsule as well as the internal vacuum tube. When transistors were good enough to be low-noise amplifiers, condenser mics could then be powered by batteries either externally (like the sony C38) or internally (like the earliest version of the Neumann U-87).
VIVA LA DIFFERENCE!
In the pre-phantom audio world, mic- and line-level SIGNALS travel on a twisted pair of wires in a balanced, differential form. This can be seen on the left side of the image as a pair of AC (alternating current) sine waves of opposite polarity. In contrast, a Common Mode signal appears as a pair of identical polarity (in-phase) sine waves (in RED).
This type of SIGNAL distribution offers the best noise immunity because balanced / differential audio INPUTS recognize the desired differential waves as SIGNAL and the pair of in-phase waves as ‘common-mode’ NOISE. The ratio of signal-to-noise is called the Common Mode Rejection Ratio or CMRR. Surprisingly, Phantom power is injected as a common mode DC signal, the beauty of which is that no modification to the existing signal distribution system was required.
ELECTRET is the electrostatic version of a magnet – holding an electrical rather than magnetic charge. When the Electret material is combined with a diaphragm, the result is an ELECTRET MICROPHONE, which, unlike a conventional studio condenser microphone, does not require a polarizing voltage for the diaphragm, but does require power for its built-in FET amplifier.
From the schematic image, there are two connections to the Electret Capsule Assembly, which contains an internal Field Effect Transistor (FET) Amplifier. External to the capsule is the FET’s ‘load’ resistor – where the audio signal will appear – the opposite side of the resistor being connected to the power source. So, that’s two of three connections, the third being ground. The signal output is unbalanced.
To visualize what is expected at the typical 1/8-inch (3.5mm) TRS Electret microphone connector, we must first consider whether the source is a mono or stereo mic. For a mono computer mic input, Creative Labs publishes the follow spec for their sound blaster card:
Input Type: Unbalanced Low Impedance
Input Sensitivity: Approx. -20dBV (100mV or 0.1Volt)
Input Impedance: 600 to 1500. (Ohms)
Input Connector: 3.5mm Miniplug (Stereo Jack)
Input Wiring: Audio on Tip, Ground on Sleeve, 5Volts DC Bias on Ring
The spec above implies that the load resistor is most likely located at the microphone. But for cameras that have a stereo mic input, also on a TRS connector, a pair of resistors will be located near the TRS input connector where the left capsule’s output will be TRS-Tip, the right capsule’s output will be TRS-Ring and ground is on TRS sleeve.
Conversations with an Australian reader helped me zoom in on the problem: audio / music store salespeople are selling Electret mics – which we know require power – as being phantom-powered! Dang! You can just imagine what happens to microphone electronics expecting 1.5 to 5.6-volts when 48-volts shows up to the party!
Well, here’s a solution I’d love to have a box of and hopefully will review in the near future…
AMBIENT Electret Mic Adapters
On Day-2 of my new blog David Prentice made this comment about LEVELS and this is coincidentally followed by a reader question…
Setting up a ‘direct line’ for questions sounds like a wonderful idea!
These days engineers are often application wise and audio signal path ignorant. Old dog concepts like gain-staging, level-matching and finding the control pot’s sweet-spot were essential to negotiating the limited dynamic range between noise-floor and distortion. Young engineers need “mentors,” more experienced engineers that can explain how things work and show how a little Knowledge can make things sound better.
Good luck on the new enterprise. (DP)
What a great setup for today’s question (ec).
I have a decent home studio setup and would like to get the most from it. I have a Tascam DM-4800 mixer that interfaces to PC via an RME 9652. (The self-rolled PC is running Cubase 4.5.2 on XP64, with plans to upgrade to cubase 6 and win7.)
The RME has 24 channels (3 ports) of lightpipe but the DM-4800 only comes with 8 channels (1 port) of adat stock. You can get more but you have to buy adat expansion cards for it. To overcome this limitation I use another audio interface, the EMU 1820m, as a converter to get 8 more channels out of the RME/Cubase rig to the DM so that I am able to mix 16 channels from the DAW – basically 8 stems. Everything is slaved to the RME clock. I have a UA LA-610 mkII for vocals and guitars, a UAD-2 and various other plug-ins as well.
Q-1: how do I need to set gain structure based upon my signal chain? I’m starting to have some success with placements on the MTV networks for shows like “Real World/Road Rules,” “Married to Rock”, and several others and would like to make my music as professional sounding as possible.
Q-2: How hot would a seasoned engineer record the signal of a sound source using my setup? Should I be recording a synth part at -0.3 dbfs or more in the -12 to -16 dbfs range so that I have more room to use eq, compression and fx?
Q-3: How does recording at full scale affect the mixing process? What I notice, and what concerns me, is that if I have a synth going and then add rhythm guitar the mix bus clip indicators immediately go red on me. Is this the product of recording too hot? Thanks for the help and super-fast reply.
Prophet Speaks Music
A-1: The most important detail is that 0dBFS = full scale = max, it’s the maximum recordable level AND the level at which the analog converters clip. To test both the AD and the DA converters (both in the Tascam DM-4800), plug a test tone into a line input and confirm that the Tascam’s metering is in agreement with Cubase’s metering. (The RME 9652 is ‘just’ the digital interface between the Tascam and Cubase and can not be calibrated.) Record this tone at 0dBFS, then -6dBFS, the -12dBFS and -18dBFS. Then play back and see what happens on the other side. You can copy the recorded track to simulate a session and confirm signal flow and headroom.
A-2: One ‘concern’ is that analog gear can have a max output that exceeds the Tascam’s input capabilities. To test / confirm, you’d want to inject a test tone into the analog gear, get the level to zero VU (0VU) on the analog meter and then see what level that shows up as on the DM’s meters. I’d expect that level to be anywhere from -16dbFS to -20dBFS. This is called NOMINAL level, which on a VU meter / Analog gear is +4dBu.
A-3: Analog gear has a minimum of 14dB to 18dB of headroom above Nominal and often more. The last thing you want to do is overdrive the converters, but IF you wanted to drive the analog gear a little harder, you’d need to insert a pad between the analog gear and the front end of the DM-4800.
I think there are rules being developed for mixing TV commercial audio, and as I understand it, TV programs and Films use -20dBFS as their dialogue reference level – this reserves headroom for the ‘suprise’ of sound effects.
A-4: It sounds like you are recording very hot, ‘across the board’ considering that you say it’s so easy to overload the mix buss. Recording level is program dependent, so you might try recording drums at -6dBFS max and other instruments an additional 6dB lower at -12dBFS.
A-5: If you need more headroom, try looking for a level trim option. EQ plugs on Protools and Adobe Audition have an additional GAIN control that allows overall LEVEL to be reduced to compensate for drastic EQ boosting. Surely Cubase EQ plugs have such an option. PT also has a Level TRIM plug, which, if you have one, can be placed BEFORE the EQ plug. The LEVEL TRIM PLUG can also be used as a “Line Attenuator, or PAD,’ reducing the overall level as a way to keep the faders up in a range where they have more ‘physical’ resolution.
A-6: When mixing, you should avoid overloading the mix buss at all costs. Try this: allow at least 6dB of headroom for the drums – peaks that are no higher than -6dBFS – and 12dB of headroom for instruments and vocals. I submix drums, bass and drum verb / ambience in both the digital and the analog domain. Doing that with other groups – instruments, vocals, etc – allows more overall level control. Please know that pulling the master fader down will not solve an overloaded mix buss.
Let me know if this helps and feel free to provide screen shots.
PS: I wrote this article on AUDIO LEVELS many years ago – It’s due for a rewrite (hopefully soon).
Ellis and I wrote back and forth a few times to clarify details. That dialogue was integrated into this correspondence. Ellis’s first response was “Wow,” and ‘thanks for the quick and awesome response!’
For years, I have been helping people solve problems by remote control. When it’s stuff I don’t know intimately, my clients and I learn together. From there it seems a natural progression to bring this private interaction into the light of a public forum – a.k.a. this new blog, Ask Eddie – the essence of which will be distilled into my new monthly column of the same name.
Now it’s your turn to ask a question…
“What do you wanna know more about?” You provide links, schematics and images in advance and I’ll do my best to fill in the gaps by hunting, gathering, annotating and hopefully answering your question. When depth is required, a link to Geek-speak articles will be provided. Deal?
You can comment below the strawberry pic OR email firstname.lastname@example.org
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