Design of nf electron-valve stereo amplifier

Tato diplomová práce se zabývá koncepcí nízkofrekvenčního elektronkového stereofonního zesilovače pro elektrofonickou kytaru. Zesilovač obsahuje dva samostatné koncové stupně s elektronkami EL34 ve třídě AB o výkonu 40W. Je vybaven dvěma kanály, korekcemi, paralelní efektovou smyčkou, přepínáním výkonu pomocí sníženého anodového napětí, volbou elektronkového nebo diodového usměrňovače. Předzesilovač je monofonní a stereofonie je dosaženo rozdělením signálu v efektové smyčce pomocí zařazeného efektu. Toto neobvyklé řešení se liší jak od klasických monofonních koncepcí, tak od stereofonních koncových zesilovačů, které předzesilovače neobsahují. Poskytuje však uživateli možnost stereofonie, aniž by musel dělit signál z nástroje ještě před vstupem zesilovače. Použitím monofonního efektového zařízení bude zvuk z reproboxu na jedné straně efektovaný, na druhé bez efektu, použitím stereofonního efektového zařízení bude zvuk z reproboxů na obou stranách efektovaný. Zesilovač lze použít i jako čistě výkonový stupeň, při zapojení externího předzesilovače do návratu efektové smyčky. U každého bloku zesilovače jsou diskutována možná řešení a pak vybráno to nejvhodnější. Největší pozornost je pak věnována návrhu a výpočtu síťového a výstupního transformátoru a ergonomickému rozložení prvků pro dosažení co největšího odstupu S/N. Obvody zesilovače byly simulovány v programu Micro-Cap 9.0 a Tonestack 1.3. Při konstrukci byl kladen důraz na správné stínění a vedení společného zemního vodiče. Po sestavení zesilovače byla prověřena jeho stabilita, změřeny kmitočtové charakteristiky pomocí osciloskopu a zkreslení pomocí distortion meteru.This master’s thesis is dealing with low frequency all valve stereo amplifier unit conception for an electric guitar. The amplifier contains two independent output stages with two power tubes EL34, working in AB class, with 40Watts of power. The apparatus is equipped with two channels, EQ correctors, parallel effects loop, output selection with lowered anode power supply, selection between silicon or tube rectifier. The preamplifier works in mono mode and the stereophony is reached by dividing the signal in an added effects system. This unusual solution differs from both monaural conceptions and binaural power amplifiers which contains no preamp. It offers the possibility of stereophony without the necessity of dividing the guitar signal before the amplifier’s input. The sound that comes from the speaker on one side is effected and on the other side is dry by using monaural effects apparatus. The sound from both speakers is effected by using binaural effect apparatus. The amplifier can be used as power amplifier stage only when the return of the effect loop is used as the amplifier input. Every available possible solution is discussed in case of each block and then the most suitable is chosen. The biggest attention is paid to a proposal and calculation of both power and output transformer, ergonomical lay-out of the stages in need of the best S/N separation. The stages were simulated in Micro-Cap 9.0 and Tonestack 1.3 computer programmes. The construction was carried out with the emphasis on proper shielding and grounding. The overall stability tests were performed after building the amplifier as well as frequency characteristics with the scope and distortion with the distortion meter.

Using the beat histogram for speech rhythm description and language identification

In this paper we present a novel approach for the description of speech rhythm and the extraction of rhythm-related features for automatic language identification (LID). Previous methods have extracted speech rhythm through the calculation of features based on salient elements of speech such as consonants, vowels and syllables. We present how an automatic rhythm extraction method borrowed from music information retrieval, the beat histogram, can be adapted for the analysis of speech rhythm by defining the most relevant novelty functions in the speech signal and extracting features describing their periodicities. We have evaluated those features in a rhythm-based LID task for two multilingual speech corpora using support vector machines, including feature selection methods to identify the most informative descriptors. Results suggest that the method is successful in describing speech rhythm and provides LID classification accuracy comparable to or better than that of other approaches, without the need for a preceding segmentation or annotation of the speech signal. Concerning rhythm typology, the rhythm class hypothesis in its original form seems to be only partly confirmed by our results

Corticomuscular Coherence Is Tuned to the Spontaneous Rhythmicity of Speech at 2-3 Hz

Human speech features rhythmicity that frames distinctive, fine-grained speech patterns. Speech can thus be counted among rhythmic motor behaviors that generally manifest characteristic spontaneous rates. However, the critical neural evidence for tuning of articulatory control to a spontaneous rate of speech has not been uncovered. The present study examined the spontaneous rhythmicity in speech production and its relationship to cortex–muscle neurocommunication, which is essential for speech control. Our MEG results show that, during articulation, coherent oscillatory coupling between the mouth sensorimotor cortex and the mouth muscles is strongest at the frequency of spontaneous rhythmicity of speech at 2–3 Hz, which is also the typical rate of word production. Corticomuscular coherence, a measure of efficient cortex–muscle neurocommunication, thus reveals behaviorally relevant oscillatory tuning for spoken language.Peer reviewe