A scheme for simple oversampled analog-to-digital (A/D) conversion using single-bit quantization is presented. The scheme is based on recording positions of zero-crossings of the input signal added to a deterministic dither function. This information can be represented in a manner such that the bit rate increases only logarithmically with the oversampling factor$r$. The input band-limited signal can be reconstructed from this information locally with$O(1/r)$pointwise error, resulting in an exponentially decaying distortion-rate characteristic.

Closed-form expressions that lower and upper bound the penalty of hybrid selection/maximal ratio combining relative to maximal ratio combining (MRC) for M-ary phase-shift keying (MPSK) modulation are proved. The bounds offer simple-to-evaluate explicit expressions, and are typically within 0.6 dB for hybrid systems with diversity order up to eight that use at least two branches, yet are independent of signal-to-noise ratio (SNR). Contrary to conclusions conjectured in a previously published paper, it is proved that the SNR penalty is not a constant, independent of SNR. It is also shown that previous estimates of the performance losses of selection diversity relative to MRC underestimate or lower bound the losses for MPSK modulation systems, and that the true loss can be significantly larger than previously believed. An upper bound to this loss is also obtained.

The problem of reconstructing a /spl pi/-bandlimited signal f from its quantized samples taken at an irregular sequence of points (t/sub k/)/sub k/spl isin//spl Zopf// arises in oversampled analog-to-digital conversion. The input signal can be reconstructed from the quantized samples (f(t/sub k/))/sub k/spl isin//spl Zopf// by estimating samples (f(n//spl lambda/))/sub n/spl isin//spl Zopf//, where /spl lambda/ is the average uniform density of the sequence (tk)/sub k/spl isin//spl Zopf//, assumed here to be greater than one, followed by linear low-pass filtering. We study three techniques for estimating samples (f(n//spl lambda/))/sub n/spl isin//spl Zopf// from quantized irregular samples (f(t/sub k/))/sub k/spl isin//spl Zopf//, including Lagrangian interpolation, and two other techniques which result in a better overall accuracy of oversampled A/D conversion.

In spite of their great potential for bandwidth saving in long distance telephony, vocoders have not found wide-spread acceptance. Two major problems have retarded their application. First is their strong electrical accent. Second is the so-called "pitch problem;" namely, deducing the nature of the talker's vocal excitation from his speech waveform. The reliability of this deduction and measurement depends critically upon high input speech-to-noise ratio, particularly between 50 and 200 cps. In many communication situations, this requirement precludes satisfactory operation. This limitation can be removed by a new method known as "voice excitations' which eliminates the necessity for a decision-making pitch detector. The principal advantage of voice excitation is its insensitivity to input signal-to-noise ratio and equalization. A voice-excited vocoder (VEV) with a 720 cps (250-970 eps) baseband and 17 spectrum channels low-passed to 25 cps each, covering the band 970-3700 cps, has been built and evaluated. The test shows an average PB-word intelligibility of 86%, compared to 92% for input speech of the same bandwidth, both with an 18 db signal-to-noise ratio. Quality tests indicate that listeners rate VEV speech "as good as" the input in about 90% of the test utterances. 0nly 19% of conventional vocoder utterances were so considered. The vocoder performed about equally well for each of the 12 speakers in the quality test. Voice-discrimination tests indicate that voice identity is well preserved. Crucial factors influencing the remade speech quality are the accuracy of spectral flattening and the impulse response of the analyzer low-pass filters. These results indicate that the principle of voice excitation provides the key to practical speech bandwidth reduction.

The problem of compatible single sideband transmission is given a precise mathematical formulation. The problem is then recognized as a combination of two problems, each of which has previously been solved. Iterative methods are required for the solution of the second problem. Examples are given illustrating one of two iteration schemes.

article Free AccessAnalogue Study of Electron Trajectories Authors: Benjamin F. Logan Massachusetts Institute of Technology, Cambridge, Mass. Massachusetts Institute of Technology, Cambridge, Mass.View Profile , George R. Welti Massachusetts Institute of Technology, Cambridge, Mass. Massachusetts Institute of Technology, Cambridge, Mass.View Profile , George C. Sponsler Massachusetts Institute of Technology, Cambridge, Mass. Massachusetts Institute of Technology, Cambridge, Mass.View Profile Authors Info & Claims Journal of the ACMVolume 2Issue 1pp 28–41https://doi.org/10.1145/320789.320793Published:01 January 1955Publication History 8citation417DownloadsMetricsTotal Citations8Total Downloads417Last 12 Months9Last 6 weeks1 Get Citation AlertsNew Citation Alert added!This alert has been successfully added and will be sent to:You will be notified whenever a record that you have chosen has been cited.To manage your alert preferences, click on the button below.Manage my AlertsNew Citation Alert!Please log in to your account Save to BinderSave to BinderCreate a New BinderNameCancelCreateExport CitationPublisher SiteeReaderPDF