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Avisoft-SASLab Pro Tutorial
How to transfer sounds from the tape recorder into the
PC
This page is addressed to those, who are not familiar with
soundcards.
For transferring sounds from the tape recorder
into the PC you first need to connect the line-out jack of the
recorder with the line-in jack of the sound card by an appropriate
cable. Sound cards usually have a 3.5mm input jack. The line-out of
the tape recorder is some times also a 3.5mm jack. So you will
probably need a cable with male 3.5mm jacks on both ends. In case
your recorder has a different line-out connector (cinch or XLR), an
appropriate adapter is required. A common sound card has usually
three connectors: microphone, line-in and line-out/speaker. So
please make sure, that you are using the correct one.
Besides the physical hardware connection described above you
have to make some adjustments by software. Launch the Recording
Control panel from the Avisoft-SASLab command "File"/"Recording
Level Control..." :
This control
window allows you to adjust the recording levels for the input
channels available on the sound card (make sure, that the level is
high enough and prevent overload). Each of these channels can be
activated separately. So make sure, that the line-in channel is
selected. To prevent any additional noise, the other channels (mic,
CD, ..) should be disabled.
At next you should start the
recording by either the command "File"/"Recording"  from the SASLab main
window or by the command "Record"/"Start (input from soundcard)"
from the Real-time
spectrograph window (can be launched from the main window by
"File"/"Real Time Spectrogram..."  ).
Take care, that
the recording level (Volume setting in the Recording Level panel) is
adjusted correctly. This is the same matter as the recording level
adjustment on your tape recorder while recording from the
microphone. Too high levels will cause clipping and distorted
recordings. Too low levels will waste the available dynamic range of
the sound card and further analysis will be affected too. Use the
recording facility of the Real time spectrograph to get maximum support for
monitoring the recording level. There is a level meter and a
clipping indication flag.
Depending on the kind of signals
to be analyzed, the sampling frequency of the sound card must be
adapted. A basic law in digital signal processing is, that the
maximum signal frequency, which can be recorded is equal to one half
of the sampling frequency. Due to the characteristic of the build-in
anti-aliasing filter of the sound card, the maximum frequency is
usually a little bit lower that one half of the sampling frequency.
That maximum frequency is also the maximum frequency visible on the
spectrogram. The frequency resolution of a spectrogram can be
computed from this formula:
resolution = sampling frequency
/ FFT length
This is the reason, why the frequency
resolution of a spectrogram with low frequency sounds is poor, when
the sampling frequency is too high. See also Selecting
appropriate spectrogram parameter settings for an example.
Therefore, the sampling frequency should be adjusted before the
sounds are transferred into the PC (command File/Sound Card
Settings...):
An alternative
way to transfer long recordings into the computer is the real-time
spectrogram window command 'Record' / 'Stream into WAV file'. Use
this command for long recordings. Overload can be easily recognized
from the waveform display (which will turn read) and the permanent
overflow flag.
For more sophisticated recording of sporadic
sound events you should use the Avisoft-RECORDER software. This
recording tool allows long-term sound-activated recording into .wav
files. A large number of various parameter settings will help to
match your specific requirements. See Avisoft RECORDER for
details. | |
