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July 31, 2020

Vance Powell desk VS Converter output




Back in the analog days, people mixed from their multitrack tape recorders into their consoles (aka “desks”), from where they routed the stereo output of the mix to a 2-track recorder. In this free excerpt from Start to Finish: Vance Powell - Episode 12 - Mixing Part 3, you’ll see Vance doing basically the same thing, except that his multitrack machine is Pro Tools, and he’s sending the output of the 2-track tape machine back into Pro Tools, in real-time. What’s cool is that at the end of the excerpt, there’s an A/B comparison that lets you clearly hear the effect of the tape machine on the sound.

Let it Flow

Vance starts by explaining the signal flow. The mix of Illiterate Light’s song “Sweat Beast,” comes out of one of the buffered output pairs on his console and is sent to an Ampex ATR-102 2-track recorder. In case you’re wondering, the signal from a buffered output first goes through a buffer amp, which matches the impedance and reduces any noise from the console circuitry.

Vance’s Ampex ATR-102, configured for 1/2” tape.

The ATR-102 will be rolling when he prints the mix, and it will be recording the signal to tape, but that’s not the final destination. The signal he’s sending to Pro Tools comes out of the repro (aka “playback”) head of the ATR-102, which is after the record head in the tape path and is reproducing the sound coming off the tape. Rather than using the Ampex ATR-102 as a destination, Vance uses it as a tape effect.

From the output of the tape machine, Vance patches the signal into a Universal Audio 2192, an A/D and D/A converter unit, which digitizes it again on the way to its final destination, a stereo track in the Pro Tools session. 

Taking Stock

Before running the mix, Vance walks over to the area of the tape machine. First, he cleans the tape heads, a task that’s normally done by his assistant. Head cleaning is advisable before every session. It involves rubbing a cotton swab dipped in a head-cleaning solution (typically 99.9 percent isopropyl alcohol) over the tape heads. The idea is to remove any oxide, dirt or other contaminants that have adhered to the heads either from the tape itself or the environment.

One of the problems Vance and others using tape these days have to deal with is that there isn’t a lot of good tape available anymore. Because it’s so rarely used anymore, only one company in the U.S. still makes reel-to-reel tape, ATR Magnetics. The company’s founder Mike Spitz passed away tragically at age 59 in 2013. Before founding ATR, Spitz was a longtime engineer at Ampex, and Vance says a lot of Ampex knowledge was lost when he died.

Vance uses a UAD 2192 for A/D and D/A conversion.

Vance says the tape he prefers to use is “new old stock” 3M 250, which was manufactured in the 1980s. As long as it’s sealed in plastic to keep it free from moisture, he says, it will be fresh when he opens it, even though it’s between 30 and 40 years old. Because there’s only a finite supply, he reuses it—although not “to death.” For this session, he’s using a reel of 250 that was still on the Ampex ATR-102 from a previous session.

Because he’s already used the tape, he says there’s a chance that running the mix through the ATR-102 could “fail spectacularly,” or could sound great.

Vance next goes to the patch bay and connects the output of the ATR-102 into the input of the 2192, and he’s ready to roll. He puts the tape machine into record, walks to the console and hits play in Pro Tools to start running the mix.

Crunchy Transients

As the mix plays, he switches between the converter output (which is fed by the tape machine) and the console output (the signal before it gets to the tape machine), and you can hear a difference. If you listen to the transients on the version coming from tape, particularly the snare drum hits, you’ll hear they’re rounded off a little, not as sharp and clean as they are coming out of the console.

Vance explains that the delay that you hear happens because the repro head is after the record head in the tape path, and those few inches of space delay the sound slightly. The delay caused by head spacing is what engineers used in the 1950s to create slapback delay effects. But that’s for another article.

Decisions, Decisions

In a fully analog project, you had to deal with at least two tape machines, the multitrack and the stereo mixdown deck. The ATR-102 was the latter, which is how Vance used it in the excerpt.

The UAD Ampex ATR-102 plug-in.

Among the variables of tape machines was the speed at which they operated. Professional machines generally featured tape speeds of 30 or 15 inches per second (ips), although some also ran at 7.5ips and 3.75ips.

As a general rule, the faster the tape moved, the more high-end reproduction and the higher the sound quality. Track width, which was related to the physical width of the tape, also had an impact on the sound. Standard tape widths included 1/4” or 1/2” tape for stereo decks and 1” or 2” tape for multitrack machines.

And then there were differences in tape formulations. Each tape had a slightly different sound and you had to calibrate the tape machine for it, to get the best-sounding results

Better Emulate Than Never

Today’s tape plug-ins offer realistic emulations of the audio characteristics of analog tape. The following examples feature the UAD Ampex ATR-102 on the mix bus (except for Ex 1a, where it’s bypassed). The plug-in is a faithful digital model of the original unit. You’ll hear the same mix excerpt in each example, so you can compare a few of the different tape settings, which emulate different tape speeds, widths and formulations. You’ll notice a pretty wide variety of sonic possibilities, and these are only some of what you can do with this plug-in.

Example 1a: Tape emulation bypassed

Example 1b: 30ips, 1” tape with GP9 formulation.

Example 1c: 15ips 1” with 468 formulation.

Example 1d: 3.75 1/4” with 111 formulation.

From left to right, the settings for Examples 1b, 1c, and 1d.