Audio Record/Playback Circuit

[The Master]

Hi, I want to make a circuit that can record short audio clips then play them back through a speaker. The playback needs to be controlled by PIC chips and the audio must be high quality.

I found a component (ISD1000A) that looks like it should do the job. Ive never done anything like this before so i would just like to know if that chip is suitable for what i want.

Im not completely sure what kind of speakers i will be using yet but i assume this device could be connected to an amp for larger speakers.

Does anyone know where to buy these chips from? I found a few webpages that sell them in large quantities but i only want about 10 of them depending on the cost. Ive still not found a site that gives me a price yet.

[ozarkshermit]

I'm not sure about the UK, but these chips (better and larger ones) are available from DIGIKEY in the US. Relatively cheap as well - a 120 second version for $10.18 US DIGIKEY # ISD17120PY-ND
240 second for $12.00 DIGIKEY # ISD17240PY-ND

Or just do a search for CHIPCORDER on DIGIKEY'S site

I'm using both - they are excellent

These were discussed in a previous thread

http://www.picbasic.co.uk/forum/showthread.php?t=9365

Ken

[The Master]

Thanks. Ive had a read through that thread and these chips seem perfect.

If i get one with an SPI interface then can i still use serial on the PIC chip? I just had a look at the datasheet for a PIC16F87 and it seems some of the SPI pins are the same as the RX/TX pins for serial. Is this the same on all PICs or would there be some that can handle both at the same time?

Edit: Im just going to read up on SPI now. Ive never used it before

[The Master]

Ive done some testing using goldwave. I encoded the most important sample using 11.025KHz (the closest option to 12KHz). The quality sounds really bad. Its like being put through a low-pass filter. Would this test be representative of those chips and if so are there any that support a higher sample rate?

[keithdoxey]

Bandwidth is half the sampling frequency so your 11K sample will only have a top end frequency of around 5.5kHz

If you want CD quality then you need to sample at 44.1kHz.

Sampling at 32kHz will give you quality similar to FM radio.

[The Master]

Im not sure what you mean there. I havnt seen bandwidth mentioned anywhere. The datasheet for these chips gives the sampling frequency (max 12KHz) and the tests i did also used sample rate.

[Ioannis]

The bandwidth (what you will hear) is the half of the sample you will take.

So for telephone quality a sample rate of 6-8khz is going to give you 3-4KHz bandwidth. What you define as filtered audio.

It is the price you have to pay for the A/D conversion in respect with he memory needed.

Ioannis

[Jerson]

For what it is worth, most of these chips are solid state alternatives for the tape in telephone answering machines. So, the quality you should expect is on par with phone quality. There may be a few variants which allow you to choose your sample rate. The APR series from Aplus Taiwan is one of such chips. Using segmentation and playing fill-ins, you can build really long messages. Some examples would be the announcement systems on the train / bus.

[The Master]

Hmm, that doesnt sound too bad then. I guess the only way i will find out for sure is to actually order some and see how they sound. If it turns out that they arent suitable then i have another idea. I seem to remember FTDI making an mp3 player chip or circuit. I know thats probably overkill for a short sample but if i used that i could use it for the longer files aswell.

I will order some of the ISD chips first though and see how they turn out. Thanks.