Feature enhancements

• Improved graphical presentation of data. 
• Peak power spectrum now supports manual and automatic reset modes. 
• Sound blaster drivers now support the higher sampling rates offered by high performance soundcards : new modes include 4kHz, 8kHz, 48kHz & 96kHz sampling rates. 
• A new octave (and sub octave) spectrum averaging feature that allows power spectrum results to be presented in a 1, 1/3, 1/6 or 1/9 octave band presentation format. 

• Stack fault when attempting to toggle the signal generator using the menu. 
• Fixed networked printer bug : when run on windows NT you could not print results to a networked printer as AtSpec could not see them. 

Improved graphical Presentation of Data

In general the graphical presentation of data in AtSpec is more than adequate for most pratical purposes, however, some aspects have led to confusion and difficulty in understanding the output. This release attempts to address the most pressing problems with the graphical display of data.

One major concern voiced by many users and potential users of AtSpec related to the labeling of graph axes. In particular many found the use of the e+/-XXX exponential notation confusing and difficult to read. Others also found that the logarithmic scale axis lacked intermediate lick mark labels in between each successive decade. Both of these concerns have been addressed with the exponential format giving way to a much more readable engineering notation using the single letter engineering prefixes corresponding to 3 decade intervals. That is using,

	f	0.000 000 000 000 001
	p	0.000 000 000 001
	n	0.000 000 001
	u	0.000 001
	m	0.001
	k	1 000
	M	1 000 000
	G	1 000 000 000
	T	1 000 000 000 000

Outside this range of exponents the conventional exponential format is used. For most practical purposes it is highly unlikely that you will ever set eyes on the old exponential format in graph axes. Note that the same engineering notation is now also used in the values reported by graph cursors and by data markers.

Another two areas of concern were with the grid lines (or lack of them) and the maximum and minimum values reported by the graph properties dialog. In particular, when referring to a decibel scale axis the maximum and minimum values were always reported and set using absolute units rather than dB. This is somewhat confusing and requires a little mental calculation to work out what absolute values are required to give a particular dB span. In this version the maximum and minimum are reported and set using dB for dB scale axes and gridlines on graphs are now supported. The figure below gives an impression of the new look of AtSpec graphs.

Continuing on in this vane the auto-scale behaviour for logarithmic and dB scaled axes could be particularly annoying in that when a graph was created and displayed for the first time it would zoom in to the full span of the function being displayed. For a particularly flat frequency response measurement this could be a displayed span of less than 1 dB. More often than not users would want to display such results on a span of say, 40dB, and have AtSpec bring the plot into view. Previously this was not possible. The auto-scaling has been rationalised and now AtSpec supports the notion of a dB span for logarithmic and dB scaled y-axes. When you create a graph you can specify the dB span and it will be honoured (provided auto-scale mode is turned off which it is by default). The figures below demonstrate the new graph properties dialog behaviour and the dB span feature when creating new graphs.

Finally when using high frequency resolution (say 32k point spectrum) it was possible to have a greater frequency resolution than the resolution of the reported data from graph cursors and markers. Specifically these were hard coded to report data in 3 decimal places precission. For higher resolutions this is obviously inadequate. Version 2.2 now allows you to change the display precision from between 1 to 15 decimal places.

Peak power spectrum reset modes

Although AtSpec has supported peak power spectrum measurement from version 2.0 the only way in which you could reset the peak power spectrum measurement buffers was to stop and re-start the analyzer which would in turn reset other spectrum results as well. In many circumstances this is particularly incovenient. Essentially what is required is a means of resetting the buffer whilst the analyzer is running. Furthermore it would also be desirable to have the buffers reset automatically after a given interval of time. Version 2.2 supports both these modes of operation which are controlled by the peak hold reset parameters in the Analyzer Options dialog box as shown below.

In auto mode the buffers are reset automatically after every Reset Count averages. In manual mode the buffers are reset only on starting the analyzer, or when the operator presses the reset button on the status bar.

Sound blaster drivers support high perfomance sound cards

It is becoming more common place to find sound cards supporting many sampling rates that are not part of original standard rates supported in the Windows multi-media interface. In particular sampling rates of 4kHz, 8kHz, 48kHz and 96kHz are not directly recognisable in Windows. However, with version 2.2 changes in the AtSpec driver architecture were made that now allow AtSpec to recognise if a particular sound card will support these non-standard sampling rates. For the most part this functions correctly although it is advisable that you verify that the sound card is actually functioning correctly in these non-standard modes before using it for measurement purposes. During testing of this feature it was found, for example, that although the driver for an ESS1869 based card reported that it supported 4kHz sampling on signal generation (wave output) it did not. In particular the signal appeared to be output at a muhc higher sampling rate than the expected 4kHz. On wave input, however, the sound card functioned correctly.

1, 1/3, 1/6 or 1/9 octave band spectrum presentation format

In many noise control & noise classification problems the ability to display power spectrum results in a sub-octave band format is indespensable. Data presented in either octave or 1/3 octave band seem to be most commonly used. For these types of measurements the typical approach is to perform spectrum analysis through octave band (sub-octave band) digital filtering using filters that conforms to ANSI standards. Such an approach applied to AtSpec would preclude the instrument from other uses concurrently (such as frequency response analysis). For this reason AtSpec takes the approach of transforming the uniformly sample power spectrum estimate that is its bread and butter into a octave/sub-octave representation. Provided that the spectrum resolution is chosen correctly this approach can and does have the accuracy of the best digital filter approach. The limitation that does arise does so because the bandwidth of the low frequency end sub-octave bands is narrower than the resolution bandwidth of the analyzer. Obviously for the band estimate to be accurate the resolution bandwidth of the analyzer must be finer than the narrowest band. AtSpec supports 1, 1/3, 1/6, and 1/9 octave band averaging modes. The minimum frequency resolution required to maintain full accuracy across the entire spectrum is summarised in the table below.

	1 Octave			1024 point
	1/3 Octave			4096 point
	1/6 Octave			8192 point
	1/9 Octave			16384 point

Note that there is no requirement that you use these resolution and band averaging combinations. The only effect of not using them will be to have some lower frequency bands "blurred" together. For example the figure below shows the third octave presentation of data obtained using only 1024 point spectrum resolution.

Version 2.1 features and enhancements news letter

Paavo Jumppanen
Author of AtSpec Spectrum Analyzer