Additional Forensics Features (Ancillary Forensics Features)

[Craig Maier]

Additional Forensics Features

There are additional tools that will be of value for forensics work which are not found in the Forensics menu. Some of them are as follows:

1. Automatic Level Control (ALC or AGC) (Dynamics Processor):

Sometimes, these algorithms or systems are referred to as Automatic Gain Controls or AGC's. This feature provides upward expansion of signals below the threshold line and downward compression of signals above the same threshold. This feature is useful in forensics applications where there is a large variation in signal levels between several different parties that may be communicating with one another. It is also useful for the broadcast of live sporting events (if you have the DC Forensics10 version of the product) in which the crowd reaction is of interest when the announcer is not speaking. Simply clicking on the ALC box in the Dynamics Processor activates this feature. The threshold, attack, and release controls are still active when this function is invoked. Many Forensics specialists have also found the automatic level control feature (ALC) in the Dynamics Processor to be very useful in their work. This feature is particularly useful for correcting near-party / far-party loudness discrepancies of recorded phone conversations and other situations where signals vary greatly from time to time.

1. Punch and Crunch Effect operating in Variable Freq Mode:

This is useful for improving the intelligibility of signals having very small values of dynamic range in the speech portion of the spectrum. It is advised that a speech filter is run first before applying this filter for enhancement. For more information, please refer to the section of this documentation that describes the Punch and Crunch effect.

1. Continuous Noise Filter:

This can be very useful for decreasing “in-band” noise found on Forensics recordings. A noise fingerprint will have to be taken from a section of the recording having only noise and no signal in order to use this filter. For more details, refer to the section on the Continuous Noise Filter.

Note: The Continuous Noise Filter in Auto-Spectrum CNF mode can often produce good results on high quality forensics audio signals that need only slight noise reduction in changing noise environments. Compare it with the results produced by the CNF Forensic AFDF mode. The Auto Spectrum CNF mode will maintain a higher level of “fidelity” compared to the AFDF mode, but will not be as effective in extremely noise situations.

1. Harmonic Reject Filter:

This is very useful for attenuating buzzes found on some recorded phone conversations. Several passes through this filter are often required for severe noise situations. Also, it is worth trying both odd and even harmonics of the fundamental buzz frequency. The fundamental buzz frequency can be found by using the Spectrum Analyzer located under the “View” menu.

1. EZ Impulse Filter:

This is very useful for eliminating static from body mike recordings transmitted via an RF carrier. It can also be useful for reducing line frequency related buzz consisting of narrow spikes having a repetition rate of 50 or 60 Hz.

1. Slot (which is a subset of the Notch) Filter:

This can be useful for isolating specific sounds buried in a recording.

1. Median Filter:

This is useful for bringing out the subtle articulations of speech in low-bandwidth or muffled voice recordings, especially when used in conjunction with its “Weighting” function.

1. Spectrum Analyzer in “High Resolution” mode:

This is useful for tape authenticity verification and other forensics analysis functions.

1. Source Time Display Window in conjunction with the Time Display found in the View Menu and the Markers found in the Marker Menu:

These are useful for precisely measuring the time between multiple events such as gunshots.

1. Live Mode is useful for surveillance situations in which signals must be cleaned up “real time.”

Please refer to the Multi-filter section of this documentation for details concerning the real-time capability of the Forensics Version of this software.

1. Live Log to Disk Mode: This is useful for recording surveillance conversations selectively while in Live, real time mode (Multi-filter).

1. High Precision Spectrum Analyzer (Please refer to the section dedicated to this feature for details.)

1. 30 Band IIR Based Graphic EQ (Please refer to the section dedicated to this feature for details.)

1. Forensics Adaptive Frequency Domain Filter (Forensics AFDF) This is the twin sister of the “Adaptive Filter” found in the Forensics menu, but uses Frequency Domain rather than Time Domain techniques to achieve its end. For details, please refer to the section in the CNF description dedicated to this function. The AFDF is found as one of the modes in the CNF within the Forensics version of this software.

1. Spectral Inverse Filter – This is useful for improving the intelligibility of muted or muffled recordings and is part of the Spectral Filter.

1. Cell Phone Noise Interference Attenuator – This is useful to reduce cell phone interference on electronic recording electronics and is found as a set of presets in the DC Forensics Multifilter.

1. Overtone Synthesizer – The Overtone Synthesizer in the Forensics version of this software uses a different set of internal filters and ranges compared to the standard version making this effect more useful for enhancing the intelligibility of garbled speech. Its range of frequency settings overlap that of the standard version (DCArt10) and so it will do things similar to that which the standard version does and more. The lower limit of the frequency setting is reduced from 3,500 Hz down to 2,000 Hz.

1. Expert Impulse Filter – This can also be used to eliminate 2-way radio static or very high frequency buzz which is at the power line frequency repetition rate (like the sound of a phase controlled light dimmer interfering with an audio system). The Vinyl LP setting is a good place to start with and the size set to 10 (on 44.1 kHz material), Threshold set to 1 and the Tracking set to around 50. Adjust the Tracking for optimal noise rejection and minimal distortion.

1. Forensics Demo - The Forensics Demo Wavefile includes a Multifilter preset using multiple (8) sub-filters cascaded together in order to clean up the audio signal. It is quite instructive to test this multifilter preset on the Forensics Demo Wavefile using the Mutifilter preset titled “Forensics Demo Clean-up Filter”. Note: (This file is an air-check disc recording made on 3-4-1933 of FDRs 1^st Inauguration speech which is buried in noise. It was recorded on a relatively low cost home RCA pre-grooved disc recorder located at a residence in Newark, NJ from AM radio station WEAF out of NYC on 660 KHz.)