"The AUDIO LOGging solution"

Author(s):
A. Palenga - DATACOMM

Industry:
ATE/Instrumentation, Electronics, Telecommunications, Industrial Controls/ Devices/ Systems, Government/Defense

Products:
Data Acquisition, LabWindows/CVI

The Challenge:
To provide a low cost, easy to use but powerful and complete hardware-software package for digital multichannel acquisition of low frequency signals, optimized for continuous and unattended data logging.

The Solution:
A simple software, executable on any common PC, that manages a NATIONAL INSTRUMENTS data acquisition board, producing the maximum hardware performance with simple and quick actions. AUDIO LOG is the solution, a user friendly and powerful package for low frequency digital recording. It acquires, records and logs up to 16 channels simultaneously using any of the 16 channels DAQ boards from NATIONAL INSTRUMENTS, including PCMCIA devices and the recent low cost M-series boards. It installs and runs on any common PC, under Windows operating system, up to XP.

Possible applications
Any needs where multiple low frequency sources have to be continuously monitored, recorded and logged, can be satisfied by AUDIO LOG, including remote monitoring systems and long term recording applications.
Typical applications are: sound and vibration data logging, phone and radio surveillance, field automatic recording of transient phenomena.

Characteristics
Every low frequency signal, with bandwidth between DC and half the channel sampling rate (selectable from 8Ks/s up to 1250 Ks/s), can be acquired and logged, with a sensitivity down to 50 mV f.s. and 16 bits resolution. (Final acquisition characteristics depend on the DAQ board used)
Up to 16 sources (single ended) can be continuously monitored and digitally recorded, in a no-loss standard WAVE format, or in a compressed MP3 format, with selectable bit rate from 32 to 128 Kbit/s.
For low performance applications, limited to 2 channels, it is possible to use the standard audio input of the PC.
Thanks to a pre-triggering technique, no-loss recording will be performed.
Full remote control is possible (see below).

Features
The application exhibits a very simple graphic interface, with language switchable among a set, available on request. The interface shows a synoptic table for a quick look and control of each channel.
All the sources are monitored graphically and up to two of them can be audio monitored via the audio output of the PC.
The channel sample rate can be settled according to the needs and the available channels are automatically enabled for use, depending upon the total sample rate capability of the board used.
Recording can be individually enabled on each channel and will start when the source level rises over the trigger threshold settled for the channel (individual or common to all channels), MP3 recording mode can be individually enabled.
Four "intelligent" filters can also be activated to post-enable the recording, depending upon the audio contents of the source: activation on generic voice, activation on limited spectra components (tone or multitones, like telegraphic signaling), avoid noisy or beat-disturbed signals recording.
A hold time can be settled, to keep recording active for a while of forever after the source level falls below the threshold. A time limit for each file can also be settled, in order to avoid too huge files; an automatic segment numbering will simplify the subsequent data collection.
The records are automatically named, based on a sequential or date-time nomenclature, and logged both in a text log, and in a graphic log that shows time traces of records and provides pan and zoom capability (see pictures).
Each channel can be freely named and all the records can be freely renamed after recording.
The operator can add his comments to channels and records, in text notes that can be reviewed at any time.
AUDIO LOG does not perform any analysis of the records: these are demanded to external packages; anyway it is possible to listen to any record by selection from the text or graphic list, also it is available an "intro mode" that allows a fast flowing through the first seconds of any records.
The file structure of the records, including text notes, is kept inside one "work directory" that can be created on any data support type, including remote disks: this strategy greatly simplifies subsequent movs, copying or deletion of the record collection.
The whole channels settings and strategy (channel names, levels, filters, enabling, hold time, sample rate and work directory) can be named and saved into a configuration file, allowing multiple strategies to be fast switched.
AUDIO LOG has a client/server architecture: the same program can act as server for remote controlled acquisition, or as client of a remote server, or as local self-controlled acquisition. The remote control can work anywhere via a TCP/IP connection and the server access is secured by a password. The audio monitoring still works in real time and data logging can be performed either on the server machine or on the client one.

Connectivity and conditioning unit
Good signal feed to the DAQ board is very important in digital acquisition: it is necessary to take care for unwanted ground return, input levels, unwanted DC coupling, anti-alias filtering.
All these features are implemented in the optional conditioning unit of the package, that provides also a very comfortable way to connect the sources, on a simple patch panel (see picture).
Moreover, it provides a monitor output, hardware switchable on any input channel, useful for local monitoring by an audio or measure device, like headphone or oscilloscope, even without the software.
The unit is totally passive: this simplifies the assembly and avoids introduction of noisy contributions.

Short characteristics are:
• 19” rack metallic chassis, 1U height
• 16 single ended inputs @ 600 Ohm
• level adjustment on each input
• inputs and output provided both on BNC and on 3.5 mm jack
• signals return insulated from the chassis and tied to the AI-SENSE of the DAQ board
• anti-aliasing 2 pole passive filters on all inputs, with cut frequency individually selectable to 4-16-32 KHz
• 50 Hz high-pass filters on all inputs and output for DC decoupling, individually selectable
• multipole DAQ board connector, suitable for the standard NATIONAL INSTRUMENTS cables.

The role of NATIONAL INSTRUMENTS products
The goal of DATACOMM was not simply to develop some ready-to-use application, to solve some particular or immediate need of acquisition; it was instead to offer a high performing general purpose application, even at low cost and user friendly, to high demanding customers.
Therefore, without the availability on the market of a complete and integrated components range like that NATIONAL INSTRUMENTS offers, probably our company never should come to this demanding design.
The role of NATIONAL INSTRUMENTS products was a decisive: the availability of good performing, low cost hardware was the first key factor; the second was our multi-year experience with the high quality and reliability of the NATIONAL INSTRUMENTS driver software, avoiding long time-consuming debugging; the third factor was the availability from the same factory of NI LabWindows/CVI, the software development environment so perfectly integrated with driver libraries, with the plus of power of C language programming; at last a decisive bonus was the availability of the mathematics libraries, including an efficient FFT algorithm, key for the implementation of filtering and compression.
With these starting points, our work was only concentrated on developing an efficient and user friendly interface for the driver, keeping all fast as possible (fighting with the operating systems), and making complete the application by all the necessary support functions, like file managing and remote control.
The recent arrival on the market of the DAQ-mx driver family greatly simplified the job to upgrade AUDIO LOG to the whole new products family: in few hours the upgrade was ready, about 1/20 of the effort for the old implementation and about 1/5 the time required to implement the even simple task of acquisition from the PC audio. Overall, I estimate that the time dedicated to the development of the DAQ section of the project was reduced about to 20% of that needed using components from other manufacturers.
So, thanks NATIONAL INSTRUMENTS and, please, leave us CVI too.

Author Information:
For more information on this Case Study, contact:
A. Palenga
DATACOMM
Tel: +39 06/5031759
datacomm2@libero.it

Browse All Case Studies »