Flashback #8: The H969 Harmonizer - Eventide Audio

Flashback #8: The H969 Harmonizer

With the success of the H949 Harmonizer’s de-glitched pitch change in 1979, our focus largely shifted towards all of the other possibilities for digital audio with a particular emphasis on reverberation, leading to the development of the world’s first general-purpose digital audio processor, the SP2016. When it came time to design the next-generation Harmonizer, we turned to engineer Jeff Sasmor to develop it.

The H969 ProPitch Harmonizer, released in 1984—five years after the H949 and nearly a decade after the H910—offered the “cleanest, highest quality pitch change ever,” as stated by the user manual. A complex device with a simple-to-use interface, the manual even came complete with an innovative Experiments section; there were 5 “experiments” users could perform to help them navigate the H969’s new features, including extended flange, repeat, reverse, and a brand new Doppler effect. The H969 also improved the accuracy and range (a whole octave wider) of the pitch change, allowing users to set precise, musical intervals of pitch shifting with the push of a button:

Engineer Chuck Zwicky recalls Prince adding the H969 to his arsenal at Paisley Park as soon as it became available. Steve Vai was also an early adopter.

“I remember that Steve Vai came to Paisley Park to meet Prince and Steve was seated in the back corner of the room, right under a little 4 space insert in the wall which housed a Quantec QRS and our H969. At one point Steve mentioned that he also had one and that he liked it for its “musical” aspects (pre-set pitch interval keys) and I said that I liked its extreme range of pitch shift.”

In fact, the H969 was one of the first pro audio products to feature “PRESETS” by including a set of 5 buttons that users could program to specific values of delay, making it easier to save and recall favorite delay settings:


To delve deeper into the development of the H969, we asked Jeff Sasmor to share his recollection of designing this device. Here’s Jeff’s Tale.


When Tony asked me to write about the H969, I only had to peer at the framed printed circuit board artwork for one of its “plug-in” modules to refresh my memory.

Internally, there was a rigid motherboard and several plug-in modules. At the time, the idea was to allow upgrading; but that never actually occurred. What did happen though, is that this architecture enabled different designers to work on different parts of the project. The H969 was one of the few Eventide products from that era that was designed by more than one person; Tony Agnello, Richard Factor, and me.

I started at Eventide as a technician in 1974, repairing DDLs, Phasers, Flangers, Omnipressors®, and of course Harmonizer® special effects units. I’d done a few designs too: the JJ-193 delay line (the letters were my dogs’ initials and 193 was my home’s street address), the phaser plug-in card for the Instant Flanger (BPC-101: Bozo Phaser Card) and, later, the BD-980 broadcast delay.

Here’s a photo of Jeff holding a framed photo of his JJ193 schematic:

Why was it framed? Because it was unlike any other hand-drawn schematic. It evoked a certain R. Crumb vibe. Take a closer look…

Now back to Jeff’s recollection…

The H969 was a complex design, and it came together based, in large part, on Tony and Richard’s ideas about how to make a better Harmonizer coupled with new processor technology that we could use to our advantage.

The most important parts of the design were de-glitching using autocorrelation to determine the best splice points and the use of two DACs to improve performance at low frequencies. A microcontroller was used to interpret the front panel switches and drive the multicolor display. A custom 2901 bit-slice processor engine, similar to that in the H949, was used for audio processing. This was in the day when a 10- or 20 MHz processor was a big deal, and there were as yet no DSP chips that could do the work.

Richard designed a clock generator using a new technique revealed in the Hewlett-Packard Journal called phase-addition synthesis. It was used to set the pitch-change ratio with even more precise control than the single-sideband arrangement in the H949. Tony designed the de-glitch circuit and the bit-slice processor. I designed the audio A/D and D/A components, integrated the system with additional logic boards, and wrote the microcontroller code and some of the 2901 firmware.

Here’s the H969’s main circuit board:

The 2901 firmware can only be compared to the internal instruction decoder of a modern-day CPU. There was no compiler or assembler: the ‘code’ was bit patterns burned into read-only memory (PROMs) and each group of bits controlled some aspect of the engine. Every minor software change during development meant programming new PROMs and throwing out the old ones. We didn’t use “lines of code,” but rather tables of code and garbage cans for errors. Talk about low-level programming!

16-bit linear A/D conversion used a new chip from Sony, the CX-20018. Tricky to use and implement, but with excellent performance for this ancient technology, it allowed us to get rid of the DBX modules that we’d been using to create virtual 16-bit performance from our home-brewed 11 bit ADCs.

In the days before ubiquitous presets, the H969 featured hard-wired buttons for delay and pitch presets. Other function buttons could be used to select flanging, delay, or pitch change. It was a great product in its day and represented the apex of digital audio technology at the time.

— Jeff Sasmor


*The H969 story would be incomplete without a Joe Shapiro asterisk. The H969 was indeed better than the H949, but, as it turned out, had about the same cost to manufacture. And the H949 remained very popular even as we introduced this new product. How could we sell the H969 without cannibalizing the H949 sales? “Simple” said Joe, at the time and for many years before and after our marketing guru, “Charge more for it! Better product, more money.” Joe is no longer with us in every sense of the word. We miss him. Here are a few words about Joe Shapiro written by Eventide founder, Richard Factor.

Thanks, Jeff! Up next, flashback #9 on the Broadcast Delay Line!

In case you missed our first flashbacks: