Ring: Bias supply +5V **
Tip: Audio signal from microphone.
It can be hard to find information about using sound card inputs, and after some research the following results are provided without any guarantees of accuracy.
| Jack connector | Item | Value |
| Microphone-in | Sensitivity: | 10mV to 200mV RMS |
| Impedance: | 600 Ohms approx | |
| Connections: | TIP Signal RING Bias (if available) SLEEVE Ground | |
| Bias: | 5V ** see below | |
| Line-in | Sensitivity: | 100mV to 2V RMS |
| Impedance: | 50K Ohms approx | |
| Line-out | Level: | 0 to 2V RMS |
| Impedance: | 10K Ohms, some cards 600 Ohms |
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Be aware that the microphone input to a sound card is mono. Do not be misled by the tip-ring-sleeve jack, the ring is used for a DC supply for the electret amplifier. |
| Sleeve: Signal Ground / Earth Ring: Bias supply +5V ** Tip: Audio signal from microphone. |
Measurements on available microphone inputs have shown that bias voltage is
often not present, and where it is its often insufficient for the electret
microphone. This may explain why in my experience PCs never provide enough
sensitivity when used with computer type microphones.
Microphone preamps built into sound cards often don't provide the same quality and signal - to - noise ratio as commercially available preamplifiers. For best quality use a separate microphone preamplifier feeding into the line input which provides two separate channels for recording.
The sampling rate and resolution (number of bits) control the frequency range and quality of the signal.
Older and cheapo sound cards are typically capable of sampling at 48 kHz with a sample resolution of 16 bits.
The sample rate (simply by dividing by 2) tells us the maximum frequency that can be allowed at the input. This is called the Nyquist criterion. The table below shows the range of sampling rate options for typical sound cards.
| Sampling rate (kHz) | Max Frequency | Quality |
| 8 | 4 kHz | telephone |
| 16 | 8 kHz | AM Radio |
| 22.05 | 11 kHz | FM Radio |
| 44.1 | 22 kHz | CD |
| 48 | 24 kHz | DAT & MP3 |
| 96 | 48 kHz |
A sound card sampling at 48kHz will cover the audio spectrum nicely, as there will be no large signals near 24kHz. At 96kHz the sound card would be able to respond to bat sounds from larger bats, but with insufficient quality for useful analysis.
The sample resolution N allows us to calculate the best possible Signal - to - Noise Ratio (SNR) for the card, as follows:
SNR(dB) = 6.02 N + 1.76
For a 16 bit card this works out to 98dB, a very reasonable figure for high quality audio. For comparison the respected Cambridge A1 audio amplifier offers a SNR of 92dB.
However this is only true if our input signal is matched to the input range of the card. This isn't appropriate for most recordings as any increase - such as a drum beat- would cause clipping. The dynamic range of live and recorded music varies but if we suppose that the difference between the loudest and softest passages is 20dB then the SNR for the softest passages falls to 78dB. Still much better than audio tape or vinyl!
External sound systems which connect via a USB2 connection offer improved isolation from interference from components inside your PC, and bring all connections within easy reach. Newer premium sound cards generally offer 24 bit sampling at 96kHz or above as for the equipment shown here.
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Delivers high definition, ultra-quiet playback and recording of audio and music with 24-bit/96kHz at 102dB SNR (Signal-to-Noise Ratio). Thanks to the excellent SNR that is at least 6 times better than most on-board audio, and lower harmonic distortion, your DVD-Audio1, CD-Audio, MP3 and other audio files sound audibly clearer and crisper than ever before. Simply hook up to your PC or notebook via easy USB connection and get set to enjoy. |