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Stage - 4


Screen Shot - Cool Edit Pro
Digital editing using Cool Edit Pro.

Editing was done on a Dell PC using Cool Edit Pro. Once all unwanted background noise has been removed from the selection, the waveform can be viewed on the PC monitor and the sound waves can be manipulated visually. Editing reel-to-reel tape involves physically cutting the medium with a razor blade, then splicing the sections. This process makes it very difficult, if not impossible, to reverse errors. Digital editing allows the option to step backwards and forwards in the editing process and to make multiple saves, thus making it very easy to repeat a process many times to get the right result. All unedited audio files were cut to CD as a reference copy and to provide a safety net to fall back on. All recordings were edited to take out unnecessary gaps and dead time and were optimized for web delivery.

To optimize audio the following filters were used in the order set out bellow:

DC Offset

DC offset is low-frequency, inaudible noise that results from equipment grounding problems. If you don’t remove it, it can skew the results of subsequent sound editing.

Dynamics Compression

Dynamics Compression
Dynamics Compression using Cool Edit Pro.

Dynamics compression evens out input levels by attenuating (turning down) the input when it rises above a specified threshold. This turns down the loudest sections. For multipurpose dynamics compression, the threshold was set to -10dB, the ratio to 4:1, and the attack and release times to 100ms. Input levels were adjusted to get approximately 3dB of compression and an output level of about 0dB.

Equalization

Parametric Eq
Adjusting Eq using Cool Edit Pro.

Equalization (Eq) changes the tone of the incoming signal by "boosting" (turning up) or "cutting" (turning down) certain frequencies. Using EQ can emphasize certain frequencies and cut others that contain noise or unwanted sound. EQ can compensate for compression Codecs that do not have flat frequency responses (that is, Codecs for which certain frequencies are not as loud after encoding). You can therefore use Eq to make a compressed clip sound as close as possible to the source recording.

graphic Eq
Rolling of unwanted Low frequencies using Cool Edit Pro.


Normalization

Normalize
Normalizing an audio file using Cool Edit Pro.

Normalization was used to maximize levels after recording and again after editing. Web audio files sound best when the digitized source has the highest possible gain without clipping. Digital audio files that do not use their full amplitude range produce low-quality streaming clips. If the amplitude range is too low, a digital sound editor can be used to adjust the range and increase the amplitude. Because some systems have trouble with files normalized to 100 percent, audio files were normalized to 95 percent of maximum, or to -0.5dB.

batch filters
Selecting batched filters using Cool Edit Pro.

Although seemingly quite involved, many of the above processes can be written to a script using Cool Edit Pro, allowing batch processing of audio files. All finished audio was saved as an uncompressed wav file (44100Hz, 16-bit, Stereo) with title, performer and copyright details attached. This TAG3 information could then be transferred to all subsequent versions of the same recording.







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STEP BY STEP GUIDE



Stage - 1
Stage - 1
Playing the original tapes using an AKAI GX 4000DB tape deck

Stage - 2
Stage - 2
Digitizing the analogue signal using soundMAX integrated digital audio

Stage - 3
Stage - 3
Reducing the background noise using fft filters

Stage - 4
Stage - 4
Editing using Cool Edit Pro

Stage - 5
Stage - 5
Creation of Mp3 files

Stage - 6
Stage - 6
Encoding for the Internet using RealNetworks Helix Producer plus 9


libraries@gateshead.gov.uk

Gateshead Central Library
Prince Consort Road, Gateshead, NE8 4LN
Tel: 0191 433 8430