The number of bits required for voice signal transmission depends on several factors, including sampling rate, bit depth, and duration of the transmission.
Standard Calculation for Voice Transmission
1. Sampling Rate:
• The standard telephone voice transmission uses Pulse Code Modulation (PCM) with a sampling rate of 8,000 samples per second (8 kHz), as per the Nyquist theorem, which states that the sampling rate must be at least twice the highest frequency of the voice signal (~4 kHz).
2. Bit Depth (Quantization):
• Each sample is typically represented using 8 bits (1 byte) in standard telephony (G.711 PCM encoding).
3. Bit Rate Calculation:
• Bit rate = Sampling rate × Bit depth
• = 8,000 samples/sec × 8 bits/sample
• = 64,000 bits per second (64 kbps)
Bits Required for Different Durations
• 1 second of voice transmission = 64,000 bits
• 1 minute of voice transmission = 64,000 × 60 = 3,840,000 bits (3.84 Mbps)
• 1 hour of voice transmission = 3.84 Mbps × 60 = 230.4 Mbps
Compression and Lower Bit Rate Codecs
To optimize bandwidth usage, modern telecommunications use compression techniques, reducing the bit rate while maintaining acceptable audio quality:
• G.729 Codec (Compressed VoIP): ~8 kbps
• G.726 Codec (ADPCM): 16-32 kbps
• AMR (Adaptive Multi-Rate, used in mobile networks): 4.75–12.2 kbps
With compression, the actual number of bits required can be significantly lower than 64 kbps, depending on the codec used.
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