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Wilmington, North Carolina once had a thriving Black middle class and an elected interracial government. In 1898 white supremacists used violence to overthrow that government, kill Black residents and drive many others from the city.
MORE →Reflects the personal views, recollections, and perspective of the author, Mike Davis.
This is a personal recollection on the Move fire on May 13, 1985
A phase vocoder is a type of vocoder-purposed algorithm which can interpolate information present in the frequency and time domains of audio signals by using phase information extracted from a frequency transform.[1] The computer algorithm allows frequency-domain modifications to a digital sound file (typically time expansion/compression and pitch shifting).
At the heart of the phase vocoder is the short-time Fourier transform (STFT), typically coded using fast Fourier transforms. The STFT converts a time domain representation of sound into a time-frequency representation (the "analysis" phase), allowing modifications to the amplitudes or phases of specific frequency components of the sound, before resynthesis of the time-frequency domain representation into the time domain by the inverse STFT. The time evolution of the resynthesized sound can be changed by means of modifying the time position of the STFT frames prior to the resynthesis operation allowing for time-scale modification of the original sound file.
The main problem that has to be solved for all cases of manipulation of the STFT is the fact that individual signal components (sinusoids, impulses) will be spread over multiple frames and multiple STFT frequency locations (bins). This is because the STFT analysis is done using overlapping analysis windows. The windowing results in spectral leakage such that the information of individual sinusoidal components is spread over adjacent STFT bins. To avoid border effects of tapering of the analysis windows, STFT analysis windows overlap in time. This time overlap results in the fact that adjacent STFT analyses are strongly correlated (a sinusoid present in analysis frame at time "t" will be present in the subsequent frames as well). The problem of signal transformation with the phase vocoder is related to the problem that all modifications that are done in the STFT representation need to preserve the appropriate correlation between adjacent frequency bins (vertical coherence) and time frames (horizontal coherence). Except in the case of extremely simple synthetic sounds, these appropriate correlations can be preserved only approximately, and since the invention of the phase vocoder research has been mainly concerned with finding algorithms that would preserve the vertical and horizontal coherence of the STFT representation after the modification. The phase coherence problem was investigated for quite a while before appropriate solutions emerged.
The phase vocoder was introduced in 1966 by Flanagan as an algorithm that would preserve horizontal coherence between the phases of bins that represent sinusoidal components.[2] This original phase vocoder did not take into account the vertical coherence between adjacent frequency bins, and therefore, time stretching with this system produced sound signals that were missing clarity.
The optimal reconstruction of the sound signal from STFT after amplitude modifications has been proposed by Griffin and Lim in 1984.[3] This algorithm does not consider the problem of producing a coherent STFT, but it does allow finding the sound signal that has an STFT that is as close as possible to the modified STFT even if the modified STFT is not coherent (does not represent any signal).
The problem of the vertical coherence remained a major issue for the quality of time scaling operations until 1999 when Laroche and Dolson[4] proposed a means to preserve phase consistency across spectral bins. The proposition of Laroche and Dolson has to be seen as a turning point in phase vocoder history. It has been shown that by means of ensuring vertical phase consistency very high quality time scaling transformations can be obtained.
The algorithm proposed by Laroche did not allow preservation of vertical phase coherence for sound onsets (note onsets). A solution for this problem has been proposed by Roebel.[5]
An example of software implementation of phase vocoder based signal transformation using means similar to those described here to achieve high quality signal transformation is Ircam's SuperVP.[6][7]
British composer Trevor Wishart used phase vocoder analyses and transformations of a human voice as the basis for his composition Vox 5 (part of his larger Vox Cycle).[8] Transfigured Wind by American composer Roger Reynolds uses the phase vocoder to perform time-stretching of flute sounds.[9] The music of JoAnn Kuchera-Morin makes some of the earliest and most extensive use of phase vocoder transformations, such as in Dreampaths (1989).[10]
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A phase vocoder is a type of vocoder-purposed algorithm which can interpolate information present in the frequency and time domains of audio signals by using phase information extracted from a frequency transform. The computer algorithm allows frequency-domain modifications to a digital sound file (typically time expansion/compression and pitch shifting). At the heart of the phase vocoder is the short-time Fourier transform (STFT), typically coded using fast Fourier transforms. The STFT converts a time domain representation of sound into a time-frequency representation (the "analysis" phase), allowing modifications to the amplitudes or phases of specific frequency components of the sound, before resynthesis of the time-frequency domain representation into the time domain by the inverse STFT. The time evolution of the resynthesized sound can be changed by means of modifying the time position of the STFT frames prior to the resynthesis operation allowing for time-scale modification of the original sound file.
The Variophone was an optical synthesizer that utilized sound waves cut onto cardboard disks rotating synchronously with a moving 35mm movie film while being photographed onto it to produce a continuous soundtrack. Afterwards this filmstrip is played as a normal movie by means of a film projector. Being read by photocell, amplified and monitored by a loudspeaker, it functions as a musical recording process. It was developed by Evgeny Sholpo in 1930 at Lenfilm Studio Productions, in Leningrad, the Soviet Union, during his experiments with graphical sound techniques, also known as ornamental, drawn, paper, artificial or synthetic sound. In his research Sholpo was assisted by the composer Georgy Rimsky‐Korsakov. Although with the first version of the Variophone, polyphonic soundtracks of up to 6 voices could be produced by shooting of several monophonic parts and combining them later, by the late 1930s and 1940s, some soundtracks contained up to twelve voices, recorded as tiny parallel tracks inside the normal soundtrack area. At the same time in the Soviet Union several other artists were experimenting with similar ideas. The first artificial soundtrack ever created was drawn in 1930 by composer and musical theorist Arseny Avraamov who was working with a hand-drawn technique for producing sound effects. Nikolai Voinov, Ter‐Gevondian and Konstantinov were developing paper sound techniques. Boris Yankovsky was developing his spectral analysis, decomposition and resynthesis technique, resembling the more erecent computer music techniques of cross synthesis and the phase vocoder. Many sound films and artificial soundtracks for movies and cartoons were produced by means of the Variophone, including the popular sound-films, often broadcast in 1930-1940s Symphony of the Piece and Torreodor. At the end of 1941 Siege of Leningrad, the Variophon was destroyed when the last missile exploded. After World War II, Evgeny Sholpo became the director of the new Scientific‐Research Laboratory for Graphical sound at the State Research Institute for Sound Recording, in Leningrad. The fourth and final version of Variophone was not finished, despite promising experiments in musical intonation and the temporal characteristics of live musical performance. The laboratory was moved to Moscow and Sholpo was removed from his position as director. In 1951, after a long illness, Evgeny Sholpo died and his laboratory was closed. Documentation for the Variophones was transferred to the Acoustical Laboratory at Moscow State Conservatory and later, to the Theremin Center. In 2007, several hours of graphical soundtracks produced with the Variophone were discovered in a Moscow film archive and await publishing.
JoAnn Kuchera-Morin (born 1951) is a professor of media arts & technology and of music. A composer and researcher specializing in multimodal interaction, she is the creator and director of the AlloSphere at the California NanoSystems Institute and the creator and director of the Center for Research in Electronic Art Technology (CREATE) at the University of California, Santa Barbara. Kuchera-Morin initiated and was chief scientist of the University of California Digital Media Innovation Program (DiMI) from 1998 to 2003. The culmination of Kuchera-Morin’s creativity and research is the AlloSphere instrument, a 30-foot-diameter, 3-story-high metal sphere inside an echo-free cube, designed for immersive, interactive scientific and artistic investigation of multi-dimensional data sets. Scientifically, the AlloSphere is an instrument for gaining insight and developing bodily intuition about environments into which the body cannot venture—abstract higher-dimensional information spaces, the worlds of the very small or very large, and the realms of the very fast or very slow. Artistically, it is an instrument for the creation and performance of avant-garde new works and the development of new modes and genres of expression and forms of immersion-based entertainment. Kuchera-Morin serves as the director of the AlloSphere Research Facility located within the California NanoSystems Institute, Elings Hall, at the University of California, Santa Barbara. Kuchera-Morin received her Ph.D. from Eastman School of Music at the University of Rochester (1984). She previously earned M.M. (1980) and B.M. degrees from the Florida State University. Kuchera-Morin's music mixes digital and acoustic instruments, such as her Concerto For Clarinet and Clarinets (1991), for solo clarinet and computer-generated tape. Her music features some of the earliest and most extensive use of phase vocoder transformations (stretching 30 seconds into 3 minutes, spectral glissandi, etc.). Dreampaths (1989) Cantata (1989) Paleo (2000), for double-bass and tape
Project 25 (P25 or APCO-25) is a suite of standards for interoperable Land mobile radio system (LMR) systems designed primarily for public safety users. The standards allow analog conventional, digital conventional, digital trunked, or mixed-mode systems. P25 was originally developed for public safety users in the United States but has also gained acceptance for security, public service, and some commercial applications worldwide. P25 radios are a replacement for analog UHF (typically FM) radios, adding the ability to transfer data as well as voice for more natural implementations of encryption and text messaging. P25 radios are commonly implemented by dispatch organizations, such as police, fire, ambulance and emergency rescue service, using vehicle-mounted radios combined with repeaters and handheld walkie-talkies. Starting around 2012, products became available with the newer Phase II modulation protocol. The older protocol known as P25 became P25 Phase I. P25 Phase II (or P25II) products use the more advanced AMBE2+ vocoder, which allows audio to pass through a more compressed bitstream and provides two TDMA voice channels in the same RF bandwidth (12.5 kHz), while Phase I can provide only one voice channel. However, P25 Phase II infrastructure can provide a "dynamic transcoder" feature that translates between Phase I and Phase II as needed. In addition to this, Phase II radios are backwards compatible with Phase I modulation and analog FM modulation, per the standard. (Phase I radios cannot operate on Phase II trunked systems. However, Phase II radios can operate on Phase I systems or conventional systems.) The European Telecommunications Standards Institute (ETSI) has created the Terrestrial Trunked Radio (TETRA) and Digital mobile radio (DMR) protocol standards, which fill a similar role to Project 25.
Before the 1921 destruction of Tulsa’s Greenwood District, Black residents had created a remarkable center of business and community life. The district included stores, professional offices, entertainment venues and homes owned by Black citizens. Understanding Greenwood means learning what was built—not only what was burned.
MORE →Madam C.J. Walker
