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Sampling is the process of measuring an audio signal at specific points in time. Sampling rate (sr) is a term used in digital audio to describe the rate or frequency at whcih a signal is peridoically samples or measured. The sampling rate or frequency is expressed in Hertz. The sampling frequency in a compact disc player is 44,100 Hertz, which means that the audio signal is sampled 44,100 times per second. The higher the sampling rate, the better the representation of the original analog wave and better the sound quality. See table below.
To calculate the maximum duration of each IC, it depends on the memory of the IC. Each of the OTP IC has memory size as below:
| Duration | 10" | 21" | 42" | 85" | 170" | 341" |
|---|---|---|---|---|---|---|
| Memory | 0.25M | 0.5M | 1M | 2M | 4M | 8M |
The general formula that gives the relation ship between the duration and sampling rate is:
Duration (in seconds) =
Memory Size of ROM (in Kb) / (Sampling rate (in KHz) x compression bits)
Note: The compression bits are ADPCM = 4 bits, PCM = 8 bits, 5-uLaw = 5 bits
For an 8M memory IC with 4 bit compression at 6 KHz sampling rate, the duration is:
Based on the sampling rate, the quality of the IC can be improved. If your application requires better quality, save the sound file at a higher sampling rate like 8 KHz or 12 KHz.
For the same 8M memory IC, if we use 8 bit compression and 12 KHz sampling rate, the duration is reduced from 341 secs to 85 secs.
| Memory | Sampling Frequency Rate | Duration | |||||
|---|---|---|---|---|---|---|---|
| 6 Khz | 8 Khz | 10 Khz | 12 Khz | ||||
| AP89010 aIVR1004 aIVR3K10 | ADPCM | 64K | 10 sec | 8 sec | 6 sec | 5 sec | D = 64K / SR |
| PCM | 32K | 5 sec | 4 sec | 3 sec | 2.5 sec | D = 32K / SR | |
| AP89021 aIVR2104 aIVR3K21 | ADPCM | 128K | 21 sec | 16 sec | 12 sec | 10 sec | D = 128K / SR |
| PCM | 32K | 10 sec | 8 sec | 6 sec | 5 sec | D = 32K / SR | |
| AP89042 aIVR4208 aIVR3K42 | ADPCM | 256K | 42 sec | 32 sec | 25 sec | 21 sec | D = 256K / SR |
| PCM | 128K | 21 sec | 16 sec | 12 sec | 10 sec | D = 128K / SR | |
| AP89085 aIVR8511 | ADPCM | 512K | 85 sec | 64 sec | 51 sec | 42 sec | D = 512K / SR |
| PCM | 256K | 42 sec | 32 sec | 25 sec | 21 sec | D = 256K / SR | |
| AP89170 | ADPCM | 1024K | 170 sec | 128 sec | 102 sec | 85 sec | D = 1024K / SR |
| PCM | 512K | 85 sec | 64 sec | 51 sec | 42 sec | D = 512K / SR | |
| AP89341 aIVR341N | ADPCM | 2048K | 341 sec | 256 sec | 204 sec | 170 sec | D = 2048K / SR |
| PCM | 1024K | 170 sec | 128 sec | 102 sec | 85 sec | D = 1024K / SR | |
| Memory | Sampling Frequency Rate | Duration | ||||
|---|---|---|---|---|---|---|
| 6 Khz | 8 Khz | 10 Khz | 12 Khz | |||
| aIVR1004 aIVR3K10 | 51.2K | 8 sec | 6 sec | 5 sec | 4 sec | D = 51.2K / SR |
| aIVR2104 aIVR3K21 |
102.4K | 17 sec | 12 sec | 10 sec | 8 sec | D = 102.4K / SR |
| aIVR4208 aIVR3K42 | 204.8K | 34 sec | 25 sec | 20 sec | 17 sec | D = 204.8K / SR |
| aIVR8511 | 409.6K | 68 sec | 51 sec | 40 sec | 34 sec | D = 409.6K / SR |
| aIVR341N | 1638.4K | 273 sec | 204 sec | 163 sec | 136 sec | D = 1638.4K / SR |
| Sampling Rate | 6 Khz | 8 Khz | 10 Khz | 11 Khz | 12 Khz |
|---|---|---|---|---|---|
| aP89010, aP89021, aP89042 | 270K | 200K | 150K | 140K | 120K |
| aP89085, aP89170, aP89341 | 270K | 190K | 150K | 140K | 120K |
| aP8910A, aP8921A, aP8942A | 344K | 252K | 202K | 183K | 168K |
| aIVRxxxx | 610K | ||||
See also PCM vs ADPCM