Tech News: Additional info about DRT's attitude and custom equipment.
- Core FAQ covers analog and digital mastering, DRT's custom gear, sample tracks and pricing.
- Background FAQ and Letters offer tips for making better mixes: compression, EQ, CDR issues.
- Custom Service is a quick summary for people who target the Major-label market.
- Tech News expands on selected technical topics.
- One-Minute Tour is where most people start.
Other items here include the Halo de-esser, EQs, Balanced Power, Halo dynamics and Console design
Why build CD mastering equipment? (when decent gear is available for less than $20K)
Welcome to the lunatic fringe of high performance audio!
This is about the more technical side of enhancing music. Note: I've made more improvements, but just haven't had time to write about them. Stay tuned...
24-Bit Converters
After using a series of stock converters over 15 years, I wanted to use a new 24-bit chipset from Crystal Semi, a name found under the hood of many top units. Crystal also makes lower-spec parts for multitrack equipment where cost is a primary factor.
Since there are fine stereo converters available in the $few-thousand price range, there are really only three reasons to build versus buy: First, you don't have to wait for manufacturers to build the latest chipset you need into their product line. You get higher performance in a shorter time, with the features you want. Second, you are not locked into extra circuitry that production units contain - buffers and signal conditioners used to deal with potentially strange sources and loads. Third, and most important, you can make design and component choices that would not be practical for a commercial unit.
For example, the 24-bit A/D is now built in as the last stage of the Halo processor. The circuit can be driven differentially, with direct coupling. This means fewer components, shorter signal path, cleaner conversion. Noise and distortion is well below 16 bit spec. When the DVD folks stop arguing and 24-bit discs become standard, the converter is ready.
On the D/A side, 24-bit 128x oversampling is excessive for the 16-bit submasters that many studios produce, but the new unit is a subtle improvement over previous ones I've tested. Another benefit is that I can customize the filter that follows the modulator. Tube or solid state, its handy to pick the circuit that suits the music.
Halo De-esser
Some projects need a lot of sparkle on the top end, without turning tweeters into aluminum confetti. In response to some challenging HipHop projects that came in during 1998, I modified the Halo processor to implement a two-stage de-esser. Stage one modifies the transfer function of the sibilance in real time, taking care of attack, and as much of the body as desired. A second VCA-based control allows for shaping the body of the excess high frequency content, without running the signal through an extra processing stage. I keep a traditional parametric de-esser for special cases, but now handle probably 90% of de-essing situations with the new circuit.
Custom EQs
The reasons I decided to build an EQ system using traditional passive components came down to flexibility, simplicity and a unique sound. In the '50s and early '60s, a few key designers - working for a literal handful of companies such as Altec and Langevin, (not the company that now owns the name) - developed EQs based on constant impedance design principles. They used parts which are unavailable today, and produced a sound that is unique. These units quickly went out of production, since they were very labor-intensive to build. Demand was not high, since recording and EQ techniques in general were still pretty basic.
Solid-state designers worked to create similar performance using fewer, lower precision components and negative feedback. Parametrics, based primarily on state-variable circuits, became common within ten years. The specs were good, the units sounded clean, and the older designs, never produced in large quantities, mostly disappeared. Many younger engineers have never heard or seen a full-blown passive EQ setup, which can include components ranging from ultra-broad shelving curves down to extremely narrowband components.
The advantage of such a system is that you can construct an EQ curve of much greater flexibility than that available via parametric circuits. The entire design can be implemented with only one line amplifier if desired, tube or solid state. Filters that are not in use literally disappear from the circuit, so the signal path can be exceptionally transparent. About the only downside is the time you can spend tweaking in just the right curve.
Balanced AC Power
Balanced AC power has had coverage in the trade press in the last few years. Equitek Co. makes excellent units, and can provide a lot of background info if you have an interest. I had Toroid Corporation of Maryland custom build the bifilar-wound transformer I needed. You can email them at sales@toroid.com for info.
Balancing your AC may not lower the noise floor of your system if you have done everything right already, but it definitely can't hurt. If you do have common-mode problems, noise of leaking bypass caps from the AC line to ground or similar annoyances, they will go away when you balance. If you interface outside gear to your setup, such as marginally-maintained guitar amps or synths, the noise floor improvement can be significant.
A lot of people report that music sounds better when the AC is balanced. Whether they can document the claim with before and after specs is another issue. My noise floor was already way down, due to the central power system that I use to distribute DC to the audio circuits, so I can't report miracle results. If anything, I gained a dB or two, depending on what kind of oddball outside gear I patched into the main signal path to test the improvement. But I'll take what I can get...
By the way, if you have a significant investment in gear, check out www.Transtector.com . They make power line spike protectors based on silicon avalanche diodes, rather than MOV's. They won't degrade over time, as MOV-based units do. You can seriously protect a full 20 amp circuit for less than $200.
Halo dynamics processing
Halo changes the transfer function of the signal path in a way that is different from conventional limiters. Probably the closest analog (no pun intended) among existing dynamics control circuits is the legendary Fairchild 670, and that comparison is not real close. Halo can bring up detail as far as 20 dB down from the main body of the signal, and manage transients faster than any variable-mu (tube or FET) limiter. It can be set to emulate the operation of devices ranging from classic radio processors like the Volumax or Gates units to more modern multiband units, and if you need it, slower attack broadband compressors.
Halo was designed initially to solve the sonic problems created by traditional designs in the top 10dB of dynamic range, where people are most sensitive. Soft/hard clippers, over-easy circuits, and VCAs or tubes changing gain create mud. Halo can emulate those gain control techniques, but reduces non-musically related harmonics and intermodulation sidebands by a factor between five and ten. While this is useful for any music style, its even more of a benefit for clients who want their disc clean but sounding loud when compared to others.
I'm deliberately vague because I'm still researching the possibilities. The Halo concept was one of those moments when a light bulb goes off in your head, and you say to yourself "Why isn't this in production somewhere?" So I had to build one. I've been asked to sell the design and/or finished units, but I'm not happy with everything yet. It's possible that Halo can be implemented in custom silicon, or be made available as a hybrid module. I need to satisfy myself that the solid state version maintains the performance of the tube device, without being cranky and time-consuming to calibrate, as the tube unit now is.
Console design
It is possible to string together some fine EQs and limiters, digital or analog, and master albums. When I first started mastering, that was my prototype setup. But when you approach the design of mastering electronics as a system, rather than a group of components, stringing it all together doesn't make sense. There are too many potential improvements to be made, especially if you are designing your own circuitry.
Some design techniques sound better, and are best implemented as a system. For example, if you need to drive a load that sinks 5 milliamps maximum, you better design the driver for an absolute minimum of 50 mils. Ten times that, or half an amp, is even better. This has implications: You will dissipate a lot of heat, consume a lot of power, your circuits can be ridiculously fast, and maybe you want to think about minimizing the number of these brutes that you really need to create your mastering chain.
No sane commercial company will build equipment to this spec, for many reasons. But if you start with a clean sheet of paper, you can forget all that. You can have central DC supplies capable of handling power amplifiers, much less line amps. You can regulate your ridiculously stable DC at the target circuit using big transistors and heat sinks. Power supply impedances in the low milliohm range are no problem. Class A circuits can idle monster currents, driving capacitive loads (which you design to be as low as possible) as if they don't exist. Everything can be DC servoed, and you know exactly what the sources and sinks look like. Frequency response from DC to RF is very attainable, if you wish. Need absurdly over-engineered capacitors or $300 switches? OK.... This is YOUR world... no compromises have to be made for ease of manufacturing, cosmetics, return on investment etc. Pure performance is the issue.
The console as it stands now is designed around a card mainframe, with signal bussing along a backplane. This is suitable for high speed digital and RF circuitry, so it works fine for audio also. As a matter of fact, its good to consider audio designs as RF ciruits that usually don't carry the bandwidth, but are designed to. Its easier to get a transparent top end.
There are other topics that will be covered here when I get a bit more time, but this gives a flavor. If you are familiar with the language of circuit design, you can write (build) things that haven't been heard before, and which make a positive contribution to people's music.
- Core FAQ covers analog and digital mastering, DRT's custom gear, sample tracks and pricing.
- Background FAQ and Letters offer tips for making better mixes: compression, EQ, CDR issues.
- Custom Service is a quick summary for people who target the Major-label market.
- Tech News expands on selected technical topics.
- One-Minute Tour is where most people start.