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Waldorf M

Wavetable Synthesizer By Rory Dow
Published April 2022

Waldorf M

Waldorf return to their roots with a modern take on the classic Microwave.

Wavetable synthesis was a revolution when it first arrived in 1978. Pioneered by Wolfgang Palm, the PPG Wavecomputer 360 was the first synthesizer to use this new technology. It had a few shortcomings, chiefly a lack of filters, that stopped it from becoming a big seller but its successor, the PPG Wave, was a hit.

The PPG Wave was the perfect marriage of digital oscillators and analogue filters, and the PPG Wave series sold well. Digital technology moves fast, however, and by the mid‑1980s, synths like the Yamaha DX7, Korg DW‑8000, and Sequential Prophet VS were offering the tempting delights of digital without the hefty price tag. PPG closed their doors in 1987.

At the same time, Waldorf Electronics GmbH, a new company created by PPG’s former German distributor, was forming. Wolfgang Palm worked with Waldorf to develop the integrated circuit chips for their first product, based on the PPG Wave. And so, in 1989, the Waldorf Microwave was released. Wavetable synthesis became Waldorf’s signature sound. The Microwave, Microwave II, Microwave XT, Wave, Blofeld, Largo, Nave, Quantum and Iridium all use wavetable synthesis, not to mention the various Eurorack modules Waldorf have released. Ask any synth fan to name a manufacturer of wavetable synths, and, more often than not, Waldorf will be the answer.

On a purely personal note, the Waldorf Microwave XT, a later version of the original Microwave, is one of my desert‑island synths. Even after 20 years of ownership, it still surprises me with sounds I could never imagine. It was with great excitement then that I received the Waldorf M for review.

What Is M?

The M is a modern recreation of the first Microwave, which has become a cult classic thanks to its combination of crunchy 8‑bit digital oscillators and smooth analogue filters. Subsequent revisions — the Microwave II and Microwave XT — moved to digital filters. Many felt they lacked the warmth of the OG. However, they did enhance sound design possibilities with a proper modulation matrix, lots of digital filter options, and enhancements to the synth engine like oscillator sync, ring modulation, FM and effects.

For better or worse, most of the Microwave II/XT improvements have not made it into the M. There are a couple of exceptions. Oscillators can work in Microwave I or Microwave II mode (more on that shortly), and sync and ring modulation are available (although only in the Microwave II oscillator mode). There is no FM, modulation matrix, or effects.

Like the Microwave, the M is an eight‑voice synthesizer. An optional voice expansion card will double the count to 16. It has two wavetable oscillators, a 24dB/oct filter (an SSI 2144 ladder design replaces the original Curtis SEM chip), analogue VCAs (stereo), four envelopes, and two LFOs. The M is also four‑part multitimbral (the OG was eight‑part, but with only eight voices; perhaps that was considered overkill).

You don’t have to look far to confirm that the M is more than just a reboot. The Microwave’s single‑knob 2U rackmount design wasn’t particularly fun to use, but the M’s spacious 440 x 305mm front panel offers plenty of hands‑on control. There’s a 3‑inch colour display and plenty of buttons to speed up navigation. Wavetable import, patch backup, and OS updates are all done via SD card. And along with the traditional MIDI DIN in, out, and thru ports, there’s a USB Type B port (for MIDI only, no audio).

The OG wavetables are all present and will sound pleasingly familiar to anyone who has ever owned a Wave, Microwave I, II or XT.

One welcome improvement is that each oscillator can now load a different wavetable instead of sharing one. Wavetables contain 64 waveforms, and there are 96 factory wavetables, plus an extra 32 slots for importing your own. The OG wavetables are all present and will sound pleasingly familiar to anyone who has ever owned a Wave, Microwave I, II or XT.

As I mentioned earlier, wavetables can work in one of two modes: MWI or MWII. These emulate the digital compression of either the Microwave I (8‑bit, 240kHz, no anti‑aliasing) or Microwave II (16‑bit, 40kHz, band‑limited). There was not as much difference in these modes as I had expected. High‑pitched sounds will exhibit different aliasing characteristics, and the 8‑bit mode does imbue some extra crunchiness on bass sounds, which is very welcome. But I doubt you would spot the difference when the synth is buried in a mix.

In MWI mode, you can even enable ‘ASIC bug mode’, which emulates a bug in the Microwave I that causes distortion if oscillator levels are above a certain threshold. This attention to detail is vital because the M is compatible with Microwave I SysEx files — great news for anyone with a sound library they want to migrate forward.


Getting around the M’s interface is simple. There are dedicated controls for key parameters, but to reach others, you tap one of the Mode buttons above the screen. For example, tap the LFO button, and you’ll see everything LFO related. Each screen combines helpful graphics (the LFO shape and frequency in this case), some information about the currently loaded patch, and labels for the four ‘soft controls’ underneath the screen. These four knobs give you access to further LFO‑related parameters. You’ll need to navigate further sub‑pages to access additional parameters.

This navigation system works well and is commonly used by other synth manufacturers. I do wish that, like many of the recent Sequential synths which use a similar approach, the screen would automatically move to the relevant page when you move a dedicated control. For example, move the filter frequency knob and automatically see the filter pages on screen. I find this speeds up sound design on the Sequential synths, and I think it would work well here too.

Presets & Wavetables

The M packs in a whopping 2048 presets, arranged in 16 banks of 128. Every preset slot can be overwritten. I can’t imagine needing that many presets for a wavetable synth, but it’s nice to have the space available. With such generous capacity, it’s a surprise that Waldorf didn’t choose to increase the number of wavetables beyond 128 (and only 32 of those are user writeable). I would have gladly traded half the preset slots for a doubling in wavetable slots.

Vladimir Salnikov, Waldorf’s DSP guru and the man behind much of the M’s operating system, gave me some information on the technical specs of its wavetable format. The first 65 wavetables are taken directly from Microwave I. In turn, the first 28 of those were taken from the PPG Wave. All wavetables are 16‑bit, but the Microwave wavetables are upsampled from 8‑bit, giving them an effective 8‑bit dynamic range for authenticity. Any new tables are true 16‑bit.

User‑imported wavetables must be 8‑bit (Vladimir tells me they hope to support 16‑bit user wavetables soon) and 256 samples per waveform. Although the M stores 64 waveforms per table, the import algorithm can cleverly handle wavetables of different lengths either by skipping periodic waves with longer wavetables or duplicating them for shorter ones. I successfully imported a few of my own. If you need to convert from another format, opening wavetables in Xfer Records’ Serum and saving them as 8‑bit .256 files works very nicely.

One peculiarity of the Microwave factory wavetable format is that the last three waveforms in every wavetable are reserved for sine, triangle and square waveforms. Both oscillators shared the same wavetable in the Microwave, so the user could use one oscillator as a true wavetable and the second for a simple ‘analogue’ waveform. With the M, I’m not sure it makes sense anymore as you can select different wavetables for each oscillator. The real problem with having these waveforms at the end of every wavetable is that if you use, say, an LFO to sweep the wavetable position, it is easy to end up with a glitch whenever the LFO pushes the position into the top three waveforms. The Microwave II/XT introduced an intelligent parameter called ‘Limit’, which stopped any modulation from selecting these three waveforms, resulting in guaranteed glitch‑free modulation. Although it wasn’t in the OS version I was sent to review, Waldorf tell me that this Limit function will be coming in a future update, which is excellent news.

The M measures 440 x 305 x 85mm and weighs in at a reassuringly weighty 5.7kg.The M measures 440 x 305 x 85mm and weighs in at a reassuringly weighty 5.7kg.

Dial M For Modulation

Modulation remains very similar to the original. There are two ADSR envelopes (for VCA and VCF), an eight‑point loopable Wave envelope (for wavetable position), a four‑point sustainable Free envelope, and two LFOs. Dedicated modulation slots are available in most sections of the synth. For example, in each oscillator, there are two slots for pitch modulation and two for wavetable position. The filter has two slots for frequency and one for resonance. Usually, where two slots are available, one of them can be multiplied by a second source, allowing you to, for example, control the LFO amount with a modulation wheel.

In practice, this system does offer plenty of modulation possibilities. But it does mean a lack of overview because the modulation is scattered over many sub‑pages. A modulation matrix would give a central place to see everything in a patch. Instead, we have to investigate each page and sub‑page of the synth to see what is assigned.

Modulation sources include the usual suspects: the envelopes and LFOs, and MIDI sources like mod wheel, velocity, key tracking, aftertouch and poly pressure. There’s a few fun ones, too: Inverse (a flip flop), CoinFlip (random 0 or 1), and Random (a new random value for each note).

The ADSR envelopes allow for modulation of all stages. The filter envelope has a delay option that can also be modulated. The more complex Wave and Free envelopes work using multiple pairs of level and time parameters, which string together to make multi‑point envelopes. The Wave envelope has adjustable loop points that can be placed at any of the eight points. There are also modulation slots to adjust all levels or times so it can double as a complex LFO. The Free envelope works similarly, with three time/level parameter pairs. It has sustain level after the three pairs and release time/level, and can even loop in two different places.

The LFOs offer plenty of tweakability too. Alongside the usual sine, triangle, pulse, random and S&waveforms are options to adjust delay, symmetry and humanise (randomising the frequency). The LFO speed ranges from 0.01Hz up to 62Hz via a switchable range parameter.

There is a Global LFO too, which mirrors the setting of LFO2 but doesn’t retrigger with every voice. This LFO (but curiously not the others) can sync to MIDI Clock, with an impressively wide frequency from 0.000065Hz (4 hours 15 minutes per cycle) to 160Hz (extending into audio range) depending on your bpm and clock division settings.