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comparison Audio-tone-amplitudes @ 80:8ce3bd7c0164
Audio-tone-amplitudes article written
| author | Mychaela Falconia <falcon@freecalypso.org> |
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| date | Wed, 10 Nov 2021 18:34:58 +0000 |
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| 79:468d43c0d8cb | 80:8ce3bd7c0164 |
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| 1 In our current Luna development setup, we use a wired headset (currently | |
| 2 FC-HDS4, previously iWOW's) as our primary audio device, connected to Iota EAR | |
| 3 output, and the same arrangement will be used on FC Venus, our planned successor | |
| 4 to FC Luna. The gist of the situation is that the firmware "thinks" that we are | |
| 5 in the classic handheld setup, but in reality it is a headset inserted into the | |
| 6 developer-operator's ear canal. | |
| 7 | |
| 8 The amplitudes of various audio tones emitted by the firmware through the DSP | |
| 9 need to be adjusted for this in-ear headset reality, in order to provide | |
| 10 reasonable ear comfort to the developer-operator and to prevent hearing damage. | |
| 11 The "classic" amplitudes for fw-generated audio tones (-7 to -5 dBfs) make sense | |
| 12 for a true phone handset with a 32 ohm earpiece speaker, and furthermore, these | |
| 13 "classic" tone amplitudes are only appropriate when the tones are generated | |
| 14 while the user holds the phone away from her ear - otherwise they are too loud. | |
| 15 But in our use case where an FC-HDS4 headset stays in the developer-operator's | |
| 16 ear canal for an entire work session, we need much lower tone amplitudes. | |
| 17 | |
| 18 Basic keybeep: the empirically found amplitude for operator comfort is -26 dBfs | |
| 19 for each of the two single tones. | |
| 20 | |
| 21 DTMF keybeep: the empirically found amplitude for operator comfort is -29 dBfs | |
| 22 for the low tone and -27 dBfs for the high tone. | |
| 23 | |
| 24 Approximately good amplitudes for the remaining tones: | |
| 25 | |
| 26 Call waiting tone: -23 dBfs | |
| 27 Ringing tone: -28 dBfs | |
| 28 Radio acknowledge (currently unused): -26 dBfs | |
| 29 Busy/congestion/dropped: -27 dBfs | |
| 30 SIT error tone: -28 dBfs | |
| 31 | |
| 32 All of these dBfs numbers listed above should be regarded as starting points | |
| 33 for possible further tuning once we implement the necessary framework in our | |
| 34 firmware for generating audio tones at configurable amplitudes - and this | |
| 35 implementation most likely won't happen before FC Venus: Condat's entanglement | |
| 36 between audio tones and the buzzer needs to be detangled first, and that task | |
| 37 requires a platform with a working buzzer. | |
| 38 | |
| 39 With our present firmware, the only way to test different audio tone amplitudes | |
| 40 is via AT@TONE test command, which requires 16 numeric arguments. The high | |
| 41 effort of repeatedly composing these complex AT@TONE commands for each tested | |
| 42 amplitude of each tested tone creates fatigue, which then interferes with the | |
| 43 original objective of psychoacoustic testing of different amplitudes. |