Basic Information Functional Description Application Description Points to Note Others

Basic Information

 

Question 1

What compression format does the HT83 series support?

Answer

The HT83 series supports compression formats such as 8-bit PCM, 6-bit ulaw PCM, 4-bit ADPCM.

Question 2

Can the HT83 series of devices play both MIDI and WAV files?

Answer

Both types of file can be played, however for the MIDI files, after conversion using the tools, only 2 channels can be played.

Functional Description

　

Application Description

　

Question 1

Why are their changes in frequency when the volume is adjusted during sound play?

Answer

  1. 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.

  2. 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:

  1. 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.

  2. 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

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.