Euroracked

Nov 06 2010

One of my projects this past spring and summer was to assemble an analog modular synthesizer system. Those who recall my Groupshow post from last spring may remember my experience visiting Schneider’s Buro in Berlin. While that visit got me to think seriously about a system of my own, visits to the Analog Haven booth at the Winter NAMM show over the years planted the seed.

Okay, so why in 2010 would anyone consider getting an analog modular synthesizer? Many systems are essentially monophonic, there’s no memory for loading and saving patches –unless you go for the uber-expensive Buchla system– and they’re usually housed in large, bulky boxes that make them hard to travel with. For me, there were two issues: the sound and sound design possibilities, and the tactile way of working. Over the last ten years, the audio quality of software instruments has improved enormously, and better DA converters have made a big difference in what we hear when working with them. At least my ear was convinced they sounded good. In April of this year I had the opportunity to see synthesist Richard Lainhart perform in New York using his analog Buchla rig and a Haken controller. The sound was as exotic, fresh, and challenging as anything I’ve become accustomed to using software, but there was an added richness and texture that made the sound seductive. The laptop performers who followed were excellent, and their sound design was interesting and inventive, yet the quality of sound lacked the appeal of what I heard earlier. Lainhart was a tough act to follow.

One of my goals this year was to work more with controllers, to gain some sense of performing with sound. There was a certain sense of physicality that I was beginning to miss working with a computer. In doing so, I spent a lot of time programming a Lemur touchscreen controller and working out with a Monome, in addition to an assortment of physical sliders and buttons. From this, I began to get more of a sense that there was some tactile connection between myself and software like Ableton Live and Reaktor. Still, I felt somewhat removed from the actual process of creating the sound, I wanted it to feel "handmade."

Starting in the spring I did quite a bit of research on current systems, and it didn’t take long to settle on the Eurorack format. While some manufacturers like Buchla and Wiard build closed systems, where only modules they manufacture can be used, Eurorack is an open format with many smaller developers getting into the game. The system itself originated as Dieter Doepher’s A-100 system, which has become very popular with a wide range of artists because of its the cost, quality, and wide range of available modules. With a large user base, smaller independent manufacturers can justify designing and building modules for the Eurorack format. The result is that there are some very innovative implementations of traditional analog designs available.

I owe a huge debt of gratitude to Matthew Davidson, aka Stretta, for his wisdom and help in getting started. The system I ended up with is what I consider a starter system, with a combination of classic modules such as envelope generators, LFOs, and sample and hold making up the control signal path, and modules from Livewire, TipTop Audio, Maleko, Harvestman, and Cwejman making up the oscillators and filters in the audio signal path. Following advice from Stretta, I invested in a high-quality Cwejman VCA as the final output from the system, a kind of main mix bus. Rounding things out are two modules from a company called Make Noise, that take their inspiration from classic Buchla modules. The QMMG and Maths will provide some unusual twists to both the audio and control signal paths.

My work with the system is in it’s early stages, but I’ve already been using it in rehearsals to develop new ideas and sounds for pieces I’m working on with Birdsongs of the Mesozoic. I’m using Ableton Live as the centerpiece of the system, with a MIDI to control voltage converter to tempo sync the modular with Live. With the modular’s audio routed through Live, I’m able to record any ideas I come up with, making the best of both analog and digital worlds.

Here’s a list of what’s in my current system:

Doepfer A-114 Ring Modulator
Doepfer A-118 Noise/Random Generator
Doepfer A-132-3 Dual linear/exponential VCA
Doepfer A-143-2 Quad ADSR 
Doepfer A-147 LFO
Doepfer A-148 Dual S&H
Doepfer A-154 Sequencer Controller
Doepfer A-155 Sequencer
Doepfer A-156 Dual Quantizer
Doepfer A-170 Dual Slew Limiter
Doepfer A-180 Multiples 1

Make Noise QMMG
Make Noise Maths
Cwejman VCA-4mx
Bubblesound uLFO
4MS Rotating Clock Divider

Cwejman MMF1
Wiard Borg 2 FILTER
Tip Top Audio Z-2040 LP-VCF
Flight of Harmony Plague Bearer

Live Wire AFG
Tip Top Audio Z3000 mk2
Cwejman VCO-6
Harvestman Piston Honda

Kenton Pro Solo MkII MIDI to CV converter
MonoRocket Gemini 4-shelf case

One of the things I learned about Germans while in Berlin is that they love their hardware. While two of the most important music software companies on the planet, Ableton and Native Instruments, make their home in Berlin, just about everyone I met on my trip there earlier this year had at least one piece of gear that was a source of great pride. Laptop jams came into vogue around 2000 when seeing someone on stage with one was a novelty, so at this point, performing with software is taken for granted. So what gets an audience’s attention these days? Cool hardware, and not just a couple of hot-rodded speak and spells, but lots of it, piles of it.

Groupshow is a Berlin-based electronic performance collective trio that is known for extended improvisations using tables full of vintage electronic gadgets and gizmos. For CTM 2010, Groupshow put on an extended performance accompanying Andy Warhol’s film Empire. Or perhaps the film accompanied Groupshow since Empire is eight hours long and consists of a single shot of New York’s Empire State building made from 6 hours and 36 minutes of 24 fps footage slowed down to play at 16 fps. Both the film and Groupshow’s extended performance consider the issue of art as process, and as such, it was an ideal event to drop in on, not necessarily to sit through. That said, the members of Groupshow were able to coax a lot of interesting sound from their collection, and the result was something that just couldn’t possibly come from software.

 

AES New York

Nov 01 2009

The Audio Engineering Society held it’s annual convention in New York City the weekend of October 9. The event has a number of components from work group meetings that discuss proposals for various audio standards, to technical papers and workshops, as well as the mother of all professional audio trade shows. This year’s show was noticeably smaller, as the economy forced many to cut back from their usual presence. Nowhere was this more evident than the eerie absence of Digidesign. While Pro Tools 8 captured this year’s TEC award for DAW Technology, the company spent the year downsizing, losing many key engineering and management positions. Prior to the show, Digi announced Eleven, a new product for guitarists, leaving many in the pro audio community wondering if the company was shifting its attention to the potentially more lucrative mass market. While Pro Tools remains a kind of industrial standard, one wonders what might happen if an industry standard goes out of business…

While the industry as a whole is having a hard time, there’s a common thread that runs through all the players who are weathering the storm and made it to AES, they all have a real love for high quality audio, and regardless of shifting trends and economic conditions, they’re in it for the long haul. Nowhere was this more evident then at API, who manufacture high end analog mixing consoles and modules. This year theuy celebrated they’re 40th year in business with a party and concert featuring guitarist Sonny Landreth with guest Bob Weir of Grateful Dead fame. Their slogan, "celebrating 40 years of ups and downs" says it all. With the rise of DAW systems and "mixing in the box" many thought the end was near for many of these manufacturers. API was quick to realize that the analog technologies they developed for high end consoles could be repurposed for the digital age. Their "lunchbox" series of preamps, EQs and compressors provides a flexible and cost effective way to assemble a high quality, analog signal path for a variety of recording and mixing scenarios.

Sonny Landreth and Bob Weir of Grateful Dead

Although AES is primarily a pro audio show, a number of musical instrument manufacturers make an appearance. Korg has a stake in both camps with their revolutionary MR series of digital recorders, a decidedly pro audio product on one hand, and their line of keyboards a dominant player in the instrument arena. This year they rolled out the SV-1, a new modeled stage keyboard that’s designed from the ground up to be a players instrument. To emphasize this, they’re promoting it with video presentations from respected players such as Neil Evans from the group Soul Live. Korg also rolled out a new version of the fabled Korg Wavedrum. The original was an innovative product that was really ahead of it’s time, and while it was a kind of secret weapon for innovative percussionists, it never really took off in the mass market. The drum itself is not a pad, but uses a drum head to provide the feel of an acoustic instrument. The drumhead serves to provide input to a physical modeling engine capable of sounds that range from organic to electronic. Korg updated the design and dropped the price, and with a renewed interest in electronic performance, this will be an important addition to just about any performer’s arsenal.

Moldover in Brooklyn

One of the real highlights of the weekend was a trip to Brooklyn’s Williamsburg district for a late Saturday night performance by Moldover, who I featured in one of my early blog posts. He’s now a resident of San Francisco, but he was on an East Coast tour supporting a new CD release Circuit Board Instrument. While Ableton Live was the engine for the show, his laptop was off to the side, out of the spot light. As a key proponent of "controllerism," Moldover believes that electronic music performance should be an entertaining visual experience for the audience, and this show was a tour de force of that aesthetic. After years hacking and customizing existing controllers, he’s now using a custom-built unit. It faces the audience and his nimble manipulation of the controls provides a clear visual connection to the sound that’s being produced. Combine this with good writing, guitar playing, and clever use of effects processing, and you get a thoroughly engaging performance.

OK, it’s time to make good on at least one of my New Year’s resolutions, and that is to keep up with my Berkleemusic blog…

That said, I wanted to reflect a bit on some trends and developments from 2008, as a kind of year-end round up. I’ll be heading to the 2009 NAMM show next week and some of these thoughts will come into clearer focus. But, for the time being, here are some of the things that caught my eye in 2008.

New Software Instruments: Circle and Alchemy

I reviewed Circle in a bog entry last July, and I’ve been very impressed with both its sound and design. While there are lot’s of powerful instruments available, Circle has really set the bar for the next generation of intuitive softsynth interfaces.

Alchemy, from Camel Audio, came in just under the wire for 2008 with it’s official December 18 release. I’m a big fan of Camel Audio products Cameleon 5000, CamelPhat and CamelSpace. They all provide unique sound design opportunities. Alchemy combines and expands on all of these products, offering the additive synthesis capabilities that Cameleon 5000 is know for, as well as granular and spectral re-synthesis capabilities. What this means is that you can import any audio file into Alchemy, analyze it for its spectral content and manipulate the individual sine wave components, as well as apply sophisticated time stretching and pitch-shifting functions. Alchemy merits it’s own review which you can look for in a future blog post. For the time being, you can check out the excellent introduction and tutorial videos on the Camel Audio site.

 
Alchemy Overview

Buzz of the year: iPhone Apps

The next big thing in music technology is mobile computing, and that can include anything from a cell phone to a laptop. The iPhone is really the first truly mobile device to provide a reliable platform for software development and distribution. Like the original Mac, developers are coming out of the woodwork with everything from card games to wedding planners. While I looked at some iPhone drum machines in an earlier blog post, there are a number of other powerful and useful apps available for the electronic musician. While the value of some are not immediately apparent, we’ve only just begun to think about how these will effect our lives as musicians.

Last October, I was in a dressing room, getting ready for a concert when I found that the battery in my tuner was dead. I prepared to head out in search of a battery an hour before the show when when one of my band mates pointed out that there was probably an iPhone app that I could use. A few minutes later I downloaded Power Tuner for about the cost of a Duracell at 7-Eleven and I was back in business.

On My iPhone:

- Beatmaker
- Bloom
- iDrum
- IR-909
- miniSynth
- Mrmr OSC controller (iTunes Store)
- Noise.io Pro
- Power Tuner (iTunes Store)
- SonicLife
- Touch the Wave
- TouchOSC


chromedecay studio look: TouchOSC with Ableton Live and BigSeq from chromedecay on Vimeo

Top Free Stuff

Native Instruments KORE Player which I reviewed earlier is still the best deal going. While the sounds included in the original player release are more general purpose, those included in the free KORE Soundpack Compilation offer a number of the more unique and interesting sounds NI is famous for. This is an absolutely must have addition for anyone producing music on a budget.

Surprise of the Year: Korg DS-10

Where did the Korg DS-10 come from? OK, game audio is a big buzz right now, but who would think of the ubiquitous Nintendo DS game device as a cutting-edge, live electronic instrument. Apparently someone at Korg Japan came up with the bright idea of developing a software version of the company’s legendary MS-10, adding a drum machine, a powerful step sequencer, and porting the whole thing to a Nintendo DS game cartridge, complete with cheat codes, BTW. Initially, this was going to be a niche item for the Japanese market, but once word of this got out, the demand became global.



The Korg DS-10 in action.
 

New Instrument: Yamaha Tenori-On

Yamaha’s Tenori-On is the coolest most revolutionary product they’ve come out with since the DX7. While that instrument introduced a completely new way to synthesize sound, the Tenori-On explores a new way for performers to interact with electronic instruments. Regardless of the myriad of possibilities posed in the early days of electronic instruments, the traditional keyboard is still the de-facto interface for playing a synthesizer. Designer Toshio Iwai wanted to create a completely new way for musicians, at all levels, to play electronic music. The result is a very sophisticated handheld system that features a 16 by 16 grid of LED buttons. These control the on-board sample-based synthesis engine as well as a 16-part step sequencer.

 
Jordan Rudess on the Tenori-On

That’s it for now. I look forward to any comments you may have. Is there anything I missed?

Modular Mood

Apr 12 2008

One of the high points of the Spring 2008 semester in the Music Technology Division at Berklee was a week-long visit from electronic musician Alessandro Cortini, best known for his work as the keyboard player for NIN. A visiting artist always presents a great opportunity for both students and teachers to get a better idea of exactly how people are working in the field. As with most visitors, I didn’t really know what to expect. I saw Allesandro play with NIN when the came through Boston in June 2006, and I did a bit of research, finding he was also part of a production/performance team called modwheelmood, but you don’t really know what someone’s going to do until they’re on campus.

Alessandro Cortini

I knew that Allesandro was doing a lot of work with modular synthesizers so I was keen on having him discuss strategies for integrating said devices into the composition/production process. On Monday afternoon he arrived to my composition seminar with his Buchla 200e modular synthesizer. What followed was a master class in the architecture, aesthetics and compositional strategies behind working with this wonderful instrument.

Alessandro Cortini’s Buchla 200e Modular Synth

There are two schools of thought regarding electronic instruments. These stem from the thinking and designs of two pioneers of early commercial synthesizers form the 1960s: Bob Moog and Don Buchla. Moog, working on the East Coast in upstate New York, felt that electronic instruments should be played by musicians, and his designs focused on the keyboard as the main connection between the player and machine. Buchla, on the other hand, was in a more free-thinking environment that was San Francisco, and he felt that the synthesizer should encourage a completely new way of developing and exploring musical ideas. (You’ll notice that Allesandro’s 200e has no keyboard controller.) From these two schools of thought came two early examples of commercially released synthesizer music. Just about everyone has heard of Wendy Carlos’ Switched On Bach that used the Moog Modular, and remains to this day, one of the best selling classical music albums of all time. Around the same time, Bay-area composer Morton Subotnick released an album called Silver Apples of the Moon, which was a showcase for the Buchla and the kind of music-making it encouraged.

Needless to say, in the mass market, the standard keyboard controller is the dominant interface for electronic music making. However, there are always those who are looking for new, unexplored or under-appreciated ways of manipulating electronic sound. Fast forward to 2008 and we find Cortini, who’s original calling was as a guitarist, touring and collaborating with Trent Reznor and NIN. Although he covers classic keyboard, bass and guitar parts on the road with NIN, his real passion is creating unique sound textures and rhythmic patterns that are used throughout the show.
While modular synthesizers are designed for studio use and are generally don’t stand up well to life on the road, Allesandro had a system built specifically for touring by EAR–Electro Acoustic Research. Onstage, there’s a Pro Tools system running backing tracks used in the show, and the EAR modular system gets it’s timing from it, so the rhythmic patterns it generates will always be in tempo. While this might seem like an obscure technical concept, Allesandro easily demonstrated how this was done in my Advanced MIDI Production class where he clocked his Buchla 200e to Logic.

During his week at Berklee, Alessandro talked a lot about using a modular synthesizer to generate musical ideas. The heart and soul of this comes from the different ways that a modular system controls musical timing. In general, this comes from a combination voltage-controlled step sequencers, and LFOs (low frequency oscillators), where the LFOs control tempo, rates, and rhythmic divisions, and the step sequencer produces control for pitch and other levels. Both of these sources are used to trigger envelopes that shape the sound. While this might sound simple, the routings and possibilities available in a modular system staggering. Check out this clip from YouTube of Allesandro tweaking his Buchla 200e. NIN fans might hear some vaguely familiar patterns and sounds.

In future posts I’ll be referring back to Allesandro Cortini’s Berklee visit. You can hear his work on both modular synthesizer and guitar on the new NIN release Ghosts I-IV. There are some cool studio shots of the sessions up on Flickr.

OK, it’s a month later and people are still asking me about the coolest stuff I saw at the Winter NAMM 2008. So I guess I’ll have to come clean with my top 5. For those of us looking for big music technology news, trade shows are more or less sleepers. These days, fewer manufacturers time their release cycles to trade shows. Even Apple, who tries to set their trajectory in January with Steve Jobs’ MacWorld keynote, is more about getting products out the door as soon as they’re ready. So, for most music technology companies, major releases and announcements have already hit the street by January. There are some exceptions…

Although I got scooped on this one by my friend and fellow Berkleemusic blogger, Dave Franz, at the top of my list is Spectrasonics, who know a little something about drama. They skipped NAMM altogether last year while working on "something really big." The fruits of that labor saw the light of day at NAMM this year when patron saint of sound design Eric Persing rolled out Omnisphere.

Spectrasonics has been quite successful at creating powerful and evocative sampled instruments such as Atmosphere, Trilogy, and Stylus RMX. These were based on the UVI sound engine which essentially is a platform for sample playback. With the next generation of instruments, the company wanted to develop their own sound engine that would expand on sample playback and get much deeper into synthesis techniques such as granular, waveshaping, and FM. They came up with something they call the "Steam" engine. While the synthesis and modulation functions here are deep, Spectrasonics has made them immediately and easily accessible to any musician. The sound library itself is massive, comprised of the greatest hits of all their previous libraries along with a collection of new and unique samples. They showed one such sampling session for their demo where an upright piano was set on fire and carefully recorded as it went up in smoke. The sound quality was fabulous and the design was ingenious with things like a Farfisa organ graincloud sounding at once unique and familiar. The only downside of their demo was the September 15 release date. With such a build-up I didn’t meet anyone who didn’t want to leave the show with a copy tucked under their arm.

One of the biggest buzzes at the show this year was the Euphonix MC line of hardware DAW controllers. While primarily known for their high end digital consoles, Euphonix is coming out with a more modest line of products that uses their Ethernet-based EuCon DAW control protocol.

These new surfaces, the MC Mix and MC Control, are aimed at the project studio user with 999.00 and 1495.00 price tags, respectively. Currently, their main competition will be the Mackie Control units. However, a sleek, compact design, well-designed functionality, as well as the responsiveness of their high-speed control will make these units serious contenders.

Next on my list is Access. While it took a couple of years to perfect the technology behind the Access TI (totally integrated) line of Virus synthesizers, these instruments have become one the must-haves in current electronic arsenals. This year Access introduced an entry-level, stand-alone module version of the Virus TI called the Snow. To top things off, Richard Devine spent the weekend holding court at their booth, evangelizing the Virus and the newly released Atomizer companion software.

The software works alongside the Virus OS to beat slice audio input coming into the Virus, map the slices across the keyboard and provide addition processing controlled by the mod wheel and pitch bend. In the capable hands of Richard Devine this became a powerful, real-time performance tool. It looks like Access is pushing the envelope of what we can expect from a hardware synthesizer to include functions that we’d normally associate with custom laptop performance software. Atomizer will be free to all Virus TI users.

Korg had one of the coolest gadgets I saw at the show, and the closest thing to what one might call a glitch instrument. The new Kaossilator Dynamic Phrase Synthesizer takes a small Kaos pad controller and adds 100 different sounds and phrases.

An internal sequencer allows the user to assemble simple melodic/rhythmic fragments and manipulate them with the pad. The device itself is pocket sized, and while it offers little in the way of connectivity or pro features, it’s really fun to play, and downright addictive.

Somehow NAMM brings out the guitar player in everyone, and this year, Mackie’s new HotWire guitar amp was what did it for me. Legendary designer Greg Mackie reputedly spent years on this design, and the result is a remarkable combination of high and low tech in a great sounding amp. At the heart of this is analog tube circuitry. Not just one circuit, but a number of them, so that in fact, when switching between the various amp modes, the actual circuit routing changes, along with the selection of tubes used. Think of it like having a collection of tube amps at your disposal, where you can easily switch between them. In addition, the amp comes with a collection of creature comforts from a tuner and metronome, to on-board digital effects. The amp sells for 1500.00 and is expected to be available in March.

Winter NAMM 2008 Top Five Roundup.

1. Spectrasonics Atmosphere
2. Euphonix MC Controllers
3. Access Virus Snow and Atomizer software
3. Korg Kaossilator
5. Mackie HotWire Guitar amp

OK, it’s a month later and people are still asking me about the coolest stuff I saw at the Winter NAMM 2008. So I guess I’ll have to come clean with my top 5. For those of us looking for big music technology news, trade shows are more or less sleepers. These days, fewer manufacturers time their release cycles to trade shows. Even Apple, who tries to set their trajectory in January with Steve Jobs’ MacWorld keynote, is more about getting products out the door as soon as they’re ready. So, for most music technology companies, major releases and announcements have already hit the street by January. There are some exceptions…

Although I got scooped on this one by my friend and fellow Berkleemusic blogger, Dave Franz, at the top of my list is Spectrasonics, who know a little something about drama. They skipped NAMM altogether last year while working on "something really big." The fruits of that labor saw the light of day at NAMM this year when patron saint of sound design Eric Persing rolled out Omnisphere.

Spectrasonics has been quite successful at creating powerful and evocative sampled instruments such as Atmosphere, Trilogy, and Stylus RMX. These were based on the UVI sound engine which essentially is a platform for sample playback. With the next generation of instruments, the company wanted to develop their own sound engine that would expand on sample playback and get much deeper into synthesis techniques such as granular, waveshaping, and FM. They came up with something they call the "Steam" engine. While the synthesis and modulation functions here are deep, Spectrasonics has made them immediately and easily accessible to any musician. The sound library itself is massive, comprised of the greatest hits of all their previous libraries along with a collection of new and unique samples. They showed one such sampling session for their demo where an upright piano was set on fire and carefully recorded as it went up in smoke. The sound quality was fabulous and the design was ingenious with things like a Farfisa organ graincloud sounding at once unique and familiar. The only downside of their demo was the September 15 release date. With such a build-up I didn’t meet anyone who didn’t want to leave the show with a copy tucked under their arm.

One of the biggest buzzes at the show this year was the Euphonix MC line of hardware DAW controllers. While primarily known for their high end digital consoles, Euphonix is coming out with a more modest line of products that uses their Ethernet-based EuCon DAW control protocol.

These new surfaces, the MC Mix and MC Control, are aimed at the project studio user with 999.00 and 1495.00 price tags, respectively. Currently, their main competition will be the Mackie Control units. However, a sleek, compact design, well-designed functionality, as well as the responsiveness of their high-speed control will make these units serious contenders.

Next on my list is Access. While it took a couple of years to perfect the technology behind the Access TI (totally integrated) line of Virus synthesizers, these instruments have become one the must-haves in current electronic arsenals. This year Access introduced an entry-level, stand-alone module version of the Virus TI called the Snow. To top things off, Richard Devine spent the weekend holding court at their booth, evangelizing the Virus and the newly released Atomizer companion software.

The software works alongside the Virus OS to beat slice audio input coming into the Virus, map the slices across the keyboard and provide addition processing controlled by the mod wheel and pitch bend. In the capable hands of Richard Devine this became a powerful, real-time performance tool. It looks like Access is pushing the envelope of what we can expect from a hardware synthesizer to include functions that we’d normally associate with custom laptop performance software. Atomizer will be free to all Virus TI users.

Korg had one of the coolest gadgets I saw at the show, and the closest thing to what one might call a glitch instrument. The new Kaossilator Dynamic Phrase Synthesizer takes a small Kaos pad controller and adds 100 different sounds and phrases.

An internal sequencer allows the user to assemble simple melodic/rhythmic fragments and manipulate them with the pad. The device itself is pocket sized, and while it offers little in the way of connectivity or pro features, it’s really fun to play, and downright addictive.

Somehow NAMM brings out the guitar player in everyone, and this year, Mackie’s new HotWire guitar amp was what did it for me. Legendary designer Greg Mackie reputedly spent years on this design, and the result is a remarkable combination of high and low tech in a great sounding amp. At the heart of this is analog tube circuitry. Not just one circuit, but a number of them, so that in fact, when switching between the various amp modes, the actual circuit routing changes, along with the selection of tubes used. Think of it like having a collection of tube amps at your disposal, where you can easily switch between them. In addition, the amp comes with a collection of creature comforts from a tuner and metronome, to on-board digital effects. The amp sells for 1500.00 and is expected to be available in March.

Winter NAMM 2008 Top Five Roundup.

1. Spectrasonics Atmosphere
2. Euphonix MC Controllers
3. Access Virus Snow and Atomizer software
3. Korg Kaossilator
5. Mackie HotWire Guitar amp