2020. 2. 27. 00:51ㆍ카테고리 없음
AbstractThis thesis discusses a highly effective still image compression algorithm – The Embedded Zerotree Wavelets coding technique, as it is called. This technique is simple but achieves a remarkable result. The image is wavelet-transformed, symbolically coded and successive quantised, therefore the compression and transmission/storage saving can be achieved by utilising the structure of zerotree. The algorithm was first proposed by Jerome M. Shapiro in 1993, however to minimise the memory usage and speeding up the EZW processor, a Depth First Search method is used to transverse across the image rather than Breadth First Search method as initially discussed in Shapiro's paper (Shapiro, 1993).
The project's primary objective is to simulate the EZW algorithm from a basic building block of 8 by 8 matrix to a well-known reference image such Lenna of 256 by 256 matrix. Hence the algorithm performance can be measured, for instance its peak signal to noise ratio can be calculated. The software environment used for the simulation is a Very-High Speed Integrated Circuits - Hardware Description Language such Peak VHDL, PC based version.
This will lead to the second phase of the project. The secondary objective is to test the algorithm at a hardware level, such FPGA for a rapid prototype implementation only if the project time permits.
A Look Under The Hood Of PeakPeak is Novation’s new polyphonic synthesiser. It’s an eight-voice analogue-hybrid design with a total of 24 oscillators, a multi-mode filter, analogue distortion, and three discrete digital effects. But behind these headlines, Novation have gone to great lengths to innovate with both digital and analogue technologies. In this preview, we aim to reveal a little more about what’s going on under the hood; what makes Peak do what it does, and how. We’ll explore the new tech developed specifically for Peak, and highlight the point at which analogue and digital converge. Fundamental to Peak’s success were two acknowledgements.
Firstly that, while analogue synthesis has unique sonic advantages over digital counterparts, an all-analogue design can limit a synth’s overall flexibility and usability. Secondly, digital synthesiser technology still has room for improvement, so any digital elements employed should be better and more powerful than designs past.For modern synthesiser instruments, using the combination of analogue and digital makes absolute sense. “In analogue circuits, the non-linear response is where a lot of the magic happens,” says Nick Bookman, long-serving Novation Hardware Engineer. “But digital gives us much more power and control when it comes to the oscillators, modulation and effects.” As such, analogue circuitry provides warmth and character for the filters, VCAs and distortion in Peak. Digital technology provides the control, audio precision and complex processing used for routing, modulation and effects.That’s Peak in a nutshell — the best of old and new.
A real hybrid. But while this blue-sky thinking is imperative to the design, Novation were focussed on making Peak more than just a convenient unity of analogue and digital technology. They had the goal of creating a completely new synthesiser; an instrument that’s greater than the sum of its (analogue and digital) parts. The next step was good old-fashioned innovation. Central to Peak is the use of a high-powered processor component called a Field Programmable Gate Array (FPGA). In contrast to traditional DSP chips, which often need to run in pairs or quads, the FPGA is a single processor on which many functions can run — from oscillators to the modulation matrix. The key benefit to an FPGA is that it runs at a much higher rate than DSP-based technology, and this has a direct impact on the clarity of sound.Each of Peak’s eight voices has an independent oversampling digital-to-analogue converter (DAC).
These DAC’s are oversampling at over 24MHz (24 million times per second), using a simple RC (resistor-capacitor) filter on their output in the analogue domain. In itself this is not new technology, but their integration inside the FPGA has enabled their design to be extended to enable optimum waveform synthesis. Because other virtual synths use discrete ‘off the shelf’ DAC chips, which are restricted to running at sample rates of either 48kHz or perhaps 96kHz, they often have aliasing issues, especially when synthesising higher frequencies. Peak’s ability to generate waveforms at the oversampling frequency — up to 512 times the traditional rate — ensures that Peak’s waveforms are pure at all frequencies, free from digital artifacts no matter how aggressively the pitch is modulated.
The New Oxford OscillatorThe implementation of the FPGA opens the doors to a new type of oscillator design for Peak — The New Oxford Oscillator — the design of which stems from the analogue imperative. Peak’s raw waveforms are generated using an architecture designed and realised by Chris Huggett. It employs two waveform-generating techniques: Numerically Controlled Oscillators (NCOs) and wavetables.The saw-tooth, square / pulse and triangle waveforms are generated using Numerically Controlled Oscillators (NCO’s). Of note is the sawtooth, which can be multiplied and detuned on the FPGA, generating a thick, harmonically rich ‘triple saw’. The oscillators can also output wavetable-based waveforms including two types of sine wave. On a conventional digital wavetable-based synthesiser, the waveforms are band-limited before being stored in the table.
This is to avoid unwanted aliasing. With the New Oxford Oscillator design there is no need for band limiting; the extreme oversampling means that the aliasing problem is pushed way out of the audible frequency spectrum enabling Peak to utilise mathematically pure waveforms. The first sine wave is exactly that — mathematically pure — while the second is a more colourful alternative, similar to the filtered triangle you would find on an analogue synth. The purity of combined and virtual synced waves is also superior because there is no compromise to the waveforms at the point of generation.The New Oxford Oscillator can also load 17 ‘designed’ wavetables of five waveforms each. The ‘Shape Amount’ knob on each oscillator — which controls pulse width and saw shape with the analogue waves — morphs between the five waveforms in the active wavetable row, and can be modulated by LFO1 and Env1 directly from the front panel. (Further modulation can be programmed using the mod matrix.)Each oscillator can also be synced to an ‘invisible’ virtual oscillator for creating classic analogue synced sounds without the need for slave oscillators, and set to a static frequency.
Peak Vhdl Software 2017
This is ideal for drones or using the oscillators as modulation sources. Linear FM (Frequency Modulation) is also featured, with all three oscillators available as FM paths in both analogue and wavetable modes, and thus capable of cross-modulating each other in a recursive loop.Inherent to the NCO design is pitch stability; Peak will never fall out of tune. But of course, the instabilities of an analogue design have a huge impact on the character of a synth. Warm, rich tones are often the side effect of slightly mis-tuned or fluctuating oscillators. So using specially designed algorithms — named Drift and Divergence — Peak mimics the response of analogue oscillators by introducing slight random pitch variation and per-voice offset, respectively, mimicking the often desirable imperfections and variance of VCOs.
This creates a convincing analogue feel, if you want it. Synth designers have known for some time that building a large and expansive modulation and control matrix in the analogue domain is costly and impractical. But there are significant sonic benefits of using analogue control voltage for parameter control, thanks to its smooth, seamless nature. DSP-based synths have gained a bad reputation — for good reason in some cases — for low resolution of parameter control. Undesirable steps between parameter values being major side-effects, alongside a delay caused by the processing time involved in traditional DSPs.
The FPGA’s processing prowess does away with these issues, and opens up new sonic potential.Most digital synths use standard 7-bit MIDI CCs for all their controls, sometimes resulting in audible ‘stepping’ of parameters, most notable in high-resonance filter movements and LFO speed shifts, for example. Peak employs 8-bit controls for oscillator tuning, filter cutoff, LFO speed and mixer levels, delivering ‘analogue-smooth’ filter sweeps, LFO tweaks, and pitch and level changes. High-resolution data interpolation, which runs on the FPGA makes sure the sweet spot comes back accurately every time a patch is recalled. Interpolation ensures smooth transition of all parameters, many of which use Logarithmic control law to ensure they feel naturally musical.Modulation is one of the most important features of any synthesiser. Generally, it’s best to offer as many options as possible for the maximum flexibility, and Peak’s generous modulation matrix enables this. The 16-slot modulation matrix gives each slot up to two sources, from 17 possible. Each of the 16 slots can be routed to any one of 37 destinations in both positive and negative amounts.
LFO routings offer bi-polar and uni-polar routing options too.Also key to Peak’s sonic flexibility — and less common in digital synths — is the ability for audio-rate modulation. In addition to the oscillators, the modulation sources (LFOs, Envelopes) also run inside the FPGA at the oversampling rate. As such, Peak’s LFOs can run at up to 1.6kHz — much higher than usually available.For those wanting more immediate control over Peak, Novation has made sure that complex synthesis is possible using the front panel alone.
Many of the key routings with Peak are available directly via the front panel, with dedicated controls. All the standard routings, such as Osc pitch mod and VCF modulation, are routable from envelopes and LFOs, and there are some additional options such as Ring Modulation (Osc 1–2) and Osc 3 to VCF frequency; again with dedicated front-panel controls. The Filter‘Real’ analogue circuitry is hard to beat when it comes to filter design, due to the complex nature of the interaction between input gain, cutoff and resonance. As powerful as the FPGA and New Oxford Oscillators are, Peak’s filters are 100% analogue. The eight self-resonant multimode analogue filters (one per voice), are based on the Bass Station II filter, but with increased resonance and adjustable keytracking. The filter can be switched from low-pass, high-pass and band-pass modes, with a choice of roll-off slopes: 12dB and 24dB/octave. LFO1 and Osc3 are hardwired as modulation sources, their depths accessible directly from the Filter section.
The ‘Env Depth’ control applies modulation from the Amp or Mod 1 envelope. The filters can also have the same Divergence applied as the oscillators, for subtle random offset per voice. Analogue DistortionPeak is extremely well equipped when it comes to distortion — more so than the average polysynth. Each filter has its own independent analogue pre- and post-filter distortion. The amount of pre-filter distortion applied is set using the ‘Filter Overdrive’ knob, and the post-filter distortion is adjusted in the menu. There’s a separate global distortion applied to the master output, dialled in with the ‘Distortion Level’ knob.Mixer & Analogue VCAsPeak’s Mixer section is where the levels of the three oscillators and a supplementary filtered noise generator are balanced.
It also houses a dedicated knob for applying ring modulation between Oscillators 1 and 2, and a ‘VCA Gain’ pot for levelling of the amplifier prior to filtering and effects Animate & ArpeggiatorAnimate is a feature of Peak that will be familiar to users of MiniNova and UltraNova, Novation’s two most recent polysynths. The Animate buttons work in momentary or latched (hold) mode, and can be selected as a source in the modulation matrix with up to 16 simultaneous routings per button push. Depth settings can be set in the menu, giving the user the ability to radically change Peak’s sound at the touch of a button. (Pedals can also be used to trigger Animate features.) As with most modern synths, Peak has an on-board arpeggiator.
This has seven modes, adjustable gate length, and a six-octave range. With 33 rhythmic variations, variable resolution and swing — all syncable to internal or external tempo — it can be used to easily spark ideas and add musical movement. Digital EffectsPeak features three digital effects: reverb, delay and chorus, all generated by the FPGA at a sample rate of greater than 90kHz, and of notably higher quality than their equivalents on most other synths. The reverb stands out as particularly impressive, incorporating modulation and filtering, and sounding supremely lush and expansive. Audio conversion from the analogue circuitry to digital effects and back is done via a DAC and ADC.
A front-panel Bypass button disables all three, and if the effects aren’t used, the converters don’t come into play at all. In that sense, the onboard effects are no different to plugging Peak into an external digital effects module, which would involve the same conversion process. Peak’s appearance and physical attributes help to affirm the synth’s quality, but also speak to today’s music makers. The keyboardless design not only looks contemporary, but saves on desk space with its reduced footprint. This is a serious consideration for home studio producers who may only have room for (or the desire to use) a single master keyboard, and live performers looking to keep their stage setup under control. The lack of keyboard also gives the user maximum freedom of choice as to how to trigger Peak: they can elect to use a Launchpad Pro, for example, rather than a full-size keyboard controller. Also worth noting is the weight.
With its high quality steel casing and tightly packed internals, Peak feels ‘reassuringly heavy’. Peak represents the apex of Novation’s synth technology. Though it’s cutting-edge and future-facing, it is still rooted to its heritage, with nods to Novation classics of decades past, such as the Bass Station and the SuperNova. It’s no exaggeration to say that, thanks to the New Oxford Oscillator, Peak is able to generate the full gamut of classic analogue-style tones, as well as an endless variety of more intricate digital-style sounds. It’s in large part what makes this the greatest synth we’ve ever built — a potent fusion of synthesis techniques that adds up to far more than the sum of its parts. The result is that Peak is an inspiring and highly musical instrument.
In the hands of the curious, Peak can take you where you want to go sonically and musically, and places you never knew existed.