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Basic Information
Question 1
What kind of sound files does the HT81 EasyVoice support? Answer
EasyVoice supports HOLTEK's 8/16-bit PCM format and Windows' PCM 8/16-bit Wav format.
Question 2
How is the time in seconds defined for the HT81 series of devices?
Answer
Defining the time in seconds for the HT81 series is based on a sampling frequency of 5KHz. If the sound file sampling frequency is higher than 5KHz, then a body with a larger voice capacity will need to be chosen.
Functional Description
Question 1
Can the HT81 device play MIDI files?
Answer
The HT81 is designed only to play digitised speech sounds, MIDI are unable to be played.
Question 2
How do I implement the "Tone-in" function in the HT-81R03 and provide details of how to use this function?
Answer
The way of using the Tone-in function in the HT-81R03 is as follows:
When using 2 HT-81R03 devices, only one speaker output is required when using the Tone-in function. For IO2 on the first HT-81R03 device, the Tone-in function should be selected. For IO2 on the second HT-81R03 device, the TR output should be selected. IO2 on both of the devices should be connected together. When this happens the sound for the second device will be output on the speaker of the first device (OUT1-OUT2). The relevant circuit details are shown in the datasheet.
Application Description
Question 1
Why the system frequency shifts due to the sound volume variations?
Answer
When batteries are used for an extended period their input resistance increases and output voltage will reduce in magnitude. This may cause some variations in the operation frequency of the oscillation circuit within the device. Changing the batteries will of course resolve this problem.
The large AC currents required by the speaker driver circuits may also cause variations in the power supply. Connecting a suitable electrolytic capacitor, such as 47µf, between the power supply lines will help to resolve this problem.
Question 2
Within the .wav programming software, the volume has been set to its highest level, however when the sound is played it is still too low?
Answer
In a PC multimedia environment, if a high quality speaker is
utilised, then all sounds will be heard due to the speaker's good frequency response. However, for applications such as toys, the speaker connected to the Voice IC, is often a low cost component with poor frequency response. As a result, sound energy will be lost as such speakers will not be able to replicate all the original sounds that were heard using the PC multimedia speakers, resulting in a lower volume output. In such applications, when recording, it is suggested that the frequency is adjusted by the equalizer to take into account the lower frequency response of the lower cost speakers.
Question 3
Is it normal for the temperature of the speaker driver transistor to be high?
Answer
Driving a speaker directly using a transistor is known as a class-A amplifier circuit. There should be no problem having the transistor run at a higher temperature. However to avoid this situation, it might be useful to investigate using the HT82V733 amplifier as an alternative means of driving the speakers
Question 4
If the power environment of the application circuitry is not of a high standard, will this affect the sound quality of the IC?
Answer
If the power contains noise, the sound quality will be influenced by such noise, which will be transferred from the IC power to the sound output port. One method of reducing this IC noise is to connect a 47ohm resistor between VDD of the IC and the power line and then to connect a 10uf capacitor between the VDD pin and
VSS.
Question 5
What tools are required to record a section of music from a CD to an IC?
Answer
There are two ways to record sounds from a CD onto an IC:
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Place a CD into a traditional audio CD player. Play and record the sound into the PC by using a standard PC SoundBlaster or compatible card. Software such as the standard recording program within Windows or other shareware or professional recording programs are all suitable. A file quality of 8KHz and 16-bit is recommended.
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Audio CD can be transferred to 44.KHz and 16-bit wav files from the PC. Use the program to transfer the files to a lower sampling rate suitable for the project.
Question 6
I have many .wav files with different sampling rates, if I wish to place all of them in a single HT81018 device, what can I do to enable the IC to play the .wav files at these different frequencies?
Answer
The HT81 Easyvoice does not support the playing of .wav files with different sampling rates, so all .wav files must have the same sampling rate. This problem can be resolved by first using sound editing software to modify the .wav files so that they all possess the same sampling rate before placing them into the device
Question 7
When the voice output has finished playing, why is there still several hundred ma of current flowing?
Answer
After the voice output has finished playing, the DAC circuit should be turned off by clearing bit 0 of the Voice Register to ensure that no excess current is used. If a SPEECH routine is called then the VoiceDown flag should be set to a 1 level.
Question 8
When using the Easy Voice HT81R18, why is it that when I create a *.E18 file, it is not possible to program an
OTP?
Answer
Before programming an HT81R18 OTP device, it is necessary to transform the *.E18 file into an OTP file, this can be done by using the HT-VDS81W.EXE.
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