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DIGITAL SIGNAL GENERATOR


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And Precision Audio Analyser

This is a comprehensive digital signal generator generating audio data files for use in the testing of CD players, computer sampling cards, computer 8-bit 12-bit and 16-bit A/D input cards, computer Sound Cards, 8-bit 12-bit and 16-bit D/A output cards on all Acorn computers. Please note that it will not generate sounds in real time - but rather generates audio sound files compatible with the CD digital audio standard and which are to a much higher specification than can be realised by real-time output from 16-bit sound cards within computers.

This Digital Signal Generator will be of immense use to the following categories of people:
* Computer Sound Card Design Engineers or hobbyists wishing to measure or check the specification of their Audio Sound outputting cards.
* Manufacturers and hobbyist makers of TEST CDs.
* Those wishing to create accurate sound samples for use in other programs.
* The curious eager to learn more about FFT's, probability density, and digital signals.
* Service Engineers servicing HiFi and CD players.

SPECIFICATIONS

DIGITAL SIGNAL GENERATOR


Digital Signal Generator

Waveforms - Sine, Square, Triangle, Sawtooth, Random Noise, Pink Noise, Sin/Cos quadrature, two-tone IM distortion, TDF 0.8 + 1.195 kHz, TDF 8 + 11.95 kHz, Delta Function, J-Test.

Random Noise Probability Distribution - Gaussian With Crest Factor=4, Triangular, Square, Haversine, Parzen, Welch and others.

Amplitude +12dB, +10 dB, +9dB, +7dB, +6 dB, +5dB, +4dB, +3 dB, +2dB, +1dB, 0dB, -1dB, -2dB, -3dB, -4dB, -5dB, -6dB, -7dB, -8dB, -9dB, -10dB, -20dB, -30dB, -40dB, -50dB, -60dB, -70dB, -80dB, -90dB, silence

Reference Level - 0dB fsd, -15dB fsd, or -18dB fsd to simplify setting of dBm0s. Plus 0dB, -0.1dB, -0.2dB, -0.3dB, -0.4dB, -0.5dB, -0.6dB, -0.7dB, -0.8dB, -0.9dB, -1dB, -2dB, -3dB, -4dB, -5dB, -6dB, -7dB, -8dB, -9dB, -10dB to simplify setting of small values of Amplitude

Dither - OFF - or ±2 lsb peak to peak dither with either Gaussian, Square or Triangular pdf.

Decay Time - 100 ms, 200 ms, 300 ms, 500 ms, 1 second, 2 seconds, 3 seconds, 5 seconds, 10 seconds. (60dB 'reverberation' decay).

Tone Burst - using any of the FFT window functions (Square (none), Gaussian, Triangular, Hanning, Cos Taper, Cos2, Welch & Parzen)

Modulation - AM and/or FM, using three different Modulator Waveforms (Sin, Square and Tringular), a selection of Modulation Depths from 0% to 200%, and a selection of Modulation Frequencies (1Hz to 5kHz). The modulation acts on all Waveforms except Sin+Cos. On Sin+Cos only phase setting or phase modulation is available. The modulator section also includes waveform modifiers, or waveform distorters of various kinds. [Modulation only available on 1600x1200 mode version]

Sample Frequency - standard audio frequencies for DAT & CD - 32 kHz, 44.1 kHz, 48 kHz including the new 96 kHz CD standard.

Frequencies - All ISO standard third-octave frequencies from 10 Hz to 20 kHz (to 40kHz at 96 kHz sampling frequency). That is 10, 12.5, 16, 20, 25, 31.5, 40, 50, 63, 80, 100 and their decade multiples). Selectable between ISO R266 exact or ISO R266 nominal.

Frequency Sweep Range - (LOG sweeps) 0.1 times, 0.2, 0,5, 1, 2, 5, 10, 20, 50, 100, 200, 500, 1000 and 2000 times. Plus third octave and octave sweep. Random noise cannot be frequency swept.

Dynamic range and Signal to Noise ratio of saved files - 96dB or -93dB with dither (un-weighted) [-66dBnom]
Amplitude Accuracy - 16 bits (± 0.002% fsd, or 0.0002dB fsd).
Frequency Accuracy - 30 bits fsd (WAV files) [but dependant upon CD-R recorder Xtal frequency accuracy or computer DAC Xtal frequency accuracy]
Distortion - (0.0016% at full output with dither)


Signal Measurement
Amplitude - True RMS, peak - peak, Crest Factor (CF) (all re fsd). Readout resolution 0.01dB.

Probability Density Distribution Graph
No of Bins of PDD graph - 128 (at 16-bit D/A resolution)
FFT Plot - see FFT plot.


FFT Frequency Response Graph
No of Points - 512, 1024, 2048, 4096, 8092, 16384, 32768, 65536, and 131072-point, selectable Frequency Scale - 1Hz to 22kHz, LOG or LINEAR frequency axis @ 44.1 kHz sampling frequency.
Amplitude Scales - Linear or 10dB, 20dB, 50dB, 100dB and 140dB Log.
Window Function - Square (none), Gaussian, Hanning, Cos Taper, Cos2, Welch, Parzen
Plot - Line Spectra plot (plus one-third-octave band plot on LOG frequency scale)
Filter Weightings - LIN (un-weighted), Audio Band, A-weighted, C-weighted, Rumble-A, Rumble-B, CCIR, Pink


Sound File Saving
16 bit CD double mono, 16-bit CD stereo, CD single channel stereo, CD invert one channel stereo, 16-bit mono. (All offset-binary 2's complement). Saves digital sound files in the &FB1 (WAV) format suitable for playing on the RiscPC 16 bit audio D/A card via a p.d. program called !Sampler, or for direct digital recording onto recordable CDROM blanks (CD-R discs) with a suitable CD recorder. (You could also record the sound onto DAT as played by the A/D card and !Sampler via the RiscPC, but the signal to noise ratio may be compromised by the computer).


Sound File Loading.
An audio WAV file can be loaded and be subject to the same frequency spectrum analysis. This makes it ideal for analysing almost any audio equipment.



What the reviewers said:
"In short this is a unique and highly technical piece of software set at such a low price you are in danger of dismissing it. On another platform you could easily move the decimal point in the price by at least one place to the right. If you need test tones tailored to your own specification then this is not to be missed." Mike Cook

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