Meeting Topic: Analog Tape Machine Calibration and the CLASP System
Speaker Name: Coleman Rogers & Chris Estes
Meeting Location: Mad Oak Studio, Allston MA
Boston AES Meeting
Nov. 2011
On Tues. Nov. 8th the Boston Section of the Audio Engineering Society held a dual presentation at Mad Oak Studio with Coleman Rogers and Chris Estes. Coleman Rogers began with an overview of Analog Tape Machine Calibration. He described the differences between brands/formulations of analog tape that were used over the years and how these different formulations affect the calibrated operating level.
The first item that he checked was the level, making sure the calibration signal which was fed into the track is the same as that coming out. The calibration tape is used for two playback adjustments; level and high frequency EQ. Most tape decks have a low frequency EQ adjustment for the playback head but since the alignment tape is a single track wide, each track will pick up more low-end information and may not be an accurate representation for individual tracks, which is called "fringing". The playback of low frequencies can be done later in the record process.
Azimuth is how square the head is with respect to the tape (ideally perpendicular to keep all tracks in phase). This is checked by comparing the two outer tracks and see how they line up on an oscilloscope. The process is virtually identical for both Sync and Playback heads.
The next step is to adjust the amplitude of the bias signal. Bias calibration involves is a high frequency tone that is mixed with the audio signal as it is being printed onto the tape. This is used to excite the magnetic particles in order to print to tape as strong as possible. The goal is to set the Record sensitivity and bias signal for optimum level and minimal distortion. After setting the bias, the record level is adjusted using a 1 kHz tone and subsequently a high frequency 10 kHz tone. The last step is to check the low frequency levels. Coleman recommended running the deck at 15ips (inches per second) for optimal low-end response.
CLASP is a way of utilizing an analog tape machine in a transparent way to ideally obtain the benefits of tape but none of the downside of logging takes and rewinding the tape to get back to the beginning of the take. The CLASP system integrates multi-track tape machines with Pro Tools, Cubase or Nuendo, giving users the editing and functionality of a DAW combined with analogue tape. The CLASP unit interfaces via a 24 I/O on D-Type connectors that plug in via a DAW. Users record to tape as they ordinarily would, but it the signal is monitored through Pro Tools with zero latency. The actual audio signal is delayed from the Record head to the Repro head and then recorded back into Pro Tools and time stamped so that it is realigned back in sync upon playback. All tape controls and transport controls are manipulated on the DAW via the CLASP system, which can handle up to 24 channels at a time — up to three CLASP units can be chained for 72 channels of simultaneous recording. CLASP even offers the ability to jump between tape speeds on-the-fly to audition and then print, even mixing speeds in the same project, something that's impossible in an all-analogue production.
Chris asked those in attendance to share their Pros and Cons of working with analog tape, which he listed on a whiteboard. He then eliminated the Cons one by one describing how the CLASP System worked, incorporating most of the favorable features of working with analog tape without the having to put up with the downside (Cons). He outlined the signal path of using CLASP and how a DAW needed to be set up to work with the CLASP System. After describing how CLASP works, it was put into action with the help of Ashley Shephard who ran a recording session using the CLASP and demonstrated the operational process using CLASP and the sonic differences when using the system.
Christopher Estes is the founder of Endless Analog in Nashville, TN. Estes invented the hardware and software solution, which is aimed at artists who have a purist analogue approach to recording and desire the chance to work with tape again.
Coleman Rogers moved to the Boston area in 1984 after graduating from Brown University. In 1986, he landed the Chief Engineer position at Bay Farm Sound Studios in Kingston, MA. During these years, he learned a great deal more about studio wiring and electronic repair, by working alongside many of the technicians in the area. In 1990, his career split as he became a freelance recording engineer, he began to teach music recording and production at UMASS Lowell and he also worked as a broadcast engineer for American Radio Systems. During this time, his freelance engineering took him from New York to Portland ME. He worked in some of the best studios and also developed the craft of remote recording in non-studio environments. In 1998, he took a full time repair technician position at Alactronics, specializing in analog tape machine repair, setup and alignment. He worked on the Alesis ADAT, the Tascam DA-88 and many other types of recording equipment and processing gear. In 2002, he took a job with Professional Audio Design, working on analog tape machines and analog processing, while developing audio upgrades, modifications and a taste for equipment design. In 2006, he began to work at Analog Devices Inc as an Applications Engineer in the Digital Audio Group, while still maintaining many studios around the Boston and New York City areas. He is a member of the Boston Section of the AES and serves on the Executive Committee.
Written By: Tony Schultz
