The solution in the DX7 is to represent values as base-2 logarithms because adding logarithms is equivalent to multiplying the values.Д«y applying 2 x to the sum, the logarithmic value can be converted back to a linear value. In hardware, multiplication is much slower than addition, especially with 1980s-era technology. (This is a very brief overview of FM synthesis see my previous DX7 reverse-engineering article for more details.) Logarithms and exponentials The frequency modulation is implemented by operator circuitry, which allows oscillators to perturb other oscillators.

The DX7 has 96 oscillators, so it keeps track of 96 separate phase angles these are stored in the phase accumulators. The DX7 implements this with a sine-wave table in ROM,ДЄn increment value that controls the frequency, and an adder that adds the increment to the table index (i.e. The digital implementation of frequency modulation uses a lookup table that holds a digitized sine wave.Д«y stepping an index through the table at a specific rate, you can produce a sine wave of a fixed frequency.Д«y perturbing this index with another signal, you can produce a modulated sine wave. These signals are represented as digital values throughout the system a digital-to-analog converter (DAC) turns the digital representation intoДЄn analog voltage for the synthesizer's output. The modulating signal changes the phase (and thus the frequency) of the carrier, creating complex harmonic structures. The idea is that you start with a sine wave (the carrier signal) and perturb it with another signal (the modulating signal). Instead of the analog oscillators and filters of an analog synthesizer, the DX7 generates sounds digitally, using a technique called FM synthesis. The DX7 was the first commercially successful digital synthesizer. Click this photo (or any other) for a magnified version. I discussed the chip as a whole in my previous DX7 article now I will focus onДie photo of the DX7's YM21280 Operator chip. Underneath the metal, the polysilicon wiring layer appears reddish or greenish.ДЇinally, the underlying silicon is grayish. (Power and ground are the thick metal lines.) The chip has one layer of metal, visible as the whitish lines on top. I created the high-resolution die photo below by compositing over a hundred microscope photos.ДЄround the edges, you can see the 64 bond wires attached to pads these connect the silicon die to the chip's 64 pins. In this blog post, I examine this circuit-implemented by a ROM, shifter, and other circuitry-in detail and

Which it fed to the OPS 'operator' chip that generated the sound waveforms.ДЄ key part of the OPS chip is an exponential circuit, which is used for frequency calculation and envelope application. Used two custom digital chips: the EGS 'envelope' chip generated frequency and envelope data, The Yamaha DX7 digital synthesizer was released in 1983 and became extremely popular, defining the sound of 1980s pop music.Д«ecause microprocessors weren't fast enough in the early 1980s, the DX7

Most dx7 patches made from sine waves