3,009 research outputs found
Asymmetric-spectra methods for Adaptive FM synthesis
This article provides an overview of further methods for producing hybrid natural-synthetic spectra with adaptive frequency modulation (AdFM). It focuses on three different techniques for the generation of asymmetric spectra based on single-sideband FM, asymmetric FM and Split-sideband synthesis. The first two techniques are applied to the variable delay line implementation of AdFM, whereas the third is based on an extension of the heterodyne method. The article discusses the principles involved in
each synthesis technique in good detail, providing one reference implementation for each. A number of examples are discussed, demonstrating the possibilities for a variety of digital audio effects applications
Nonlinear Distortion Synthesis Using the Split-Sideband Method, with Applications to Adaptive Signal Processing
Split-sideband synthesis (SpSB)—which is related to the well-known principles of waveshaping, single-sideband modulation, and frequency modulation—offers the possibility of creating four independent sideband outputs: upper, lower, odd, and even. Novel spectra and timbres can be created by the way in which these four outputs are combined. As with similar techniques for distortion synthesis, an SpSB process is controlled by the modulator and carrier frequencies as well as the modulation index. The technique can also be used as an adaptive effect applied to arbitrary monophonic signals. A number of sound samples illustrate the technique
Experiments with calibrated digital sideband separating downconversion
This article reports on the first step in a focused program to re-optimize
radio astronomy receiver architecture to better take advantage of the latest
advancements in commercial digital technology. Specifically, an L-Band
sideband-separating downconverter has been built using a combination of careful
(but ultimately very simple) analog design and digital signal processing to
achieve wideband downconversion of an RFI-rich frequency spectrum to baseband
in a single mixing step, with a fixed-frequency Local Oscillator and stable
sideband isolation exceeding 50 dB over a 12 degree C temperature range.Comment: 10 pages, 12 figures, to be published in PAS
New 60-cm Radio Survey Telescope with the Sideband-Separating SIS Receiver for the 200 GHz Band
We have upgraded the 60-cm radio survey telescope located in Nobeyama, Japan.
We developed a new waveguide-type sideband-separating SIS mixer for the
telescope, which enables the simultaneous detection of distinct molecular
emission lines both in the upper and lower sidebands. Over the RF frequency
range of 205-240 GHz, the single-sideband receiver noise temperatures of the
new mixer are 40-100 K for the 4.0-8.0 GHz IF frequency band. The image
rejection ratios are greater than 10 dB over the same range. For the dual IF
signals obtained by the receiver, we have developed two sets of acousto-optical
spectrometers and a telescope control system. Using the new telescope system,
we successfully detected the 12CO (J=2-1) and 13CO (J=2-1) emission lines
simultaneously toward Orion KL in 2005 March. Using the waveguide-type
sideband-separating SIS mixer for the 200 GHz band, we have initiated the first
simultaneous 12CO (J=2-1) and 13CO (J=2-1) survey of the galactic plane as well
as large-scale mapping observations of nearby molecular clouds.Comment: 15 pages, 15 figures, Accepted for publication in PASJ, version with
high resolution figures is available via
http://www.nro.nao.ac.jp/~nakajima/vst1_2sb.pd
Detection of OD towards the low-mass protostar IRAS16293-2422
Although water is an essential and widespread molecule in star-forming
regions, its chemical formation pathways are still not very well constrained.
Observing the level of deuterium fractionation of OH, a radical involved in the
water chemical network, is a promising way to infer its chemical origin. We aim
at understanding the formation mechanisms of water by investigating the origin
of its deuterium fractionation. This can be achieved by observing the abundance
of OD towards the low-mass protostar IRAS16293-2422, where the HDO distribution
is already known. Using the GREAT receiver on board SOFIA, we observed the
ground-state OD transition at 1391.5 GHz towards the low-mass protostar
IRAS16293-2422. We also present the detection of the HDO 111-000 line using the
APEX telescope. We compare the OD/HDO abundance ratio inferred from these
observations with the predictions of chemical models. The OD line is detected
in absorption towards the source continuum. This is the first detection of OD
outside the solar system. The SOFIA observation, coupled to the observation of
the HDO 111-000 line, provides an estimate of the abundance ratio OD/HDO ~
17-90 in the gas where the absorption takes place. This value is fairly high
compared with model predictions. This may be reconciled if reprocessing in the
gas by means of the dissociative recombination of H2DO+ further fractionates OH
with respect to water. The present observation demonstrates the capability of
the SOFIA/GREAT instrument to detect the ground transition of OD towards
star-forming regions in a frequency range that was not accessible before.
Dissociative recombination of H2DO+ may play an important role in setting a
high OD abundance. Measuring the branching ratios of this reaction in the
laboratory will be of great value for chemical models.Comment: 6 pages, 6 figures, 3 tables, accepted for publication in A&A
SOFIA/GREAT special issu
- …