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The A-to-D and D-to-A conversion
technologies have been applied to portable audio equipment with the
enhancement of the scale of integration of memory and the progress of
signal compression techniques.
The MP3 is one of such technologies. (It uses Compact Flash, Memory
Stick, and SD as recording media.) The following noise suppression
measures are applicable to these solid state audio players.
One of radiant noises is those from the cable from a headphone or an
earphone. The higher harmonics in an internal digital processing
circuit leaks from ground, a power supply, or a signal line to an audio
line, and are intensively radiated from a headphone cable.
Since the voice frequency is as low as 20 kHz or below, chip ferrite
beads with an impedance near 600 ohm (at 100MHz) are frequently used to
suppress radiant noise.
Since some types of ferrite may distort sound signals, however, care
must be taken to select the material. The BLM_B series accommodating
high-speed signals are recommended to prevent this.
The three-line common mode choke coil DLM2HG series have been newly
introduced to the market. The choke coil is capable of suppressing
radiant noise through a sound signal circuit and further preventing
voice distortion. |
| Noise Suppression
Model |
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 MP3
Player
Noise
level comparison on AUDIO LINE
| |
No EMI Filter
on L, R and Ground |
BLM18BB601SN
on L, R and Ground |
| Radiation |
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