PCM5242: Audio Converters Forum

Hi, Tom,

Welcome to E2E, Thanks for your interest in our products!.

The behavior you are describing is expected, as it is related to the sum of each one of the DRCs that form the 3-Band DRC. The 3-Band DRC is composed of Low, Mid and High band independent DRCs. Each one of them limits the power in a specific region of operation, delimited by the DRC filters. In general, the filters used to limit the compression region should be configured to get a flat response after summing them, however, when the input level exceeds threshold level and the DRCs starts acting, the sum of the output signals of the DRCs will overlap, generating the waveform you are observing. This can be identified in the following plot. It would be possible to mitigate the large peaks using the SmoothClip feature of HF6 at expense of THD performance.

Best Regards,

  -Diego Meléndez López
   Audio Applications Engineer

Hi Diego,

Many thanks for your comprehensive explanation and suggestion. I have tried to mitigate the large peaks using the HF6 SmoothClip -20dB. The frequency response becomes much flat but the THD would be increased up to 19.4%.

Could you please suggest the SmoothClip level to optimize the DRC frequency response and THD performance? Many thanks again.

Test condition: PCM5242 EVM,  PSIA input LRCLK=44.1kHz, MCLK=22.5792MHz, MCLK/LRCLK ratio = 512

Test result:

1. Frequency response of HF6

2. Evaluation of SmoothClip THD with input 1kHz sinewave @-10dBFS (HF6 DRC region 2 ratio 5)

THD test#	SmoothClip level dB	THD %
1	0	0.005
2	-10	0.005
3	-15	0.005
4	-18	12.57
5	-20	19.38

Hi, Tom,

The smooth clip tuning depends on the end-application requirements according to the maximum allowed peaking under a condition where he DRCs are acting. The three band DRC response can't be flat if the input of the DRCs is above the allowed threshold. The smooth clip feature can be used to limit the higher peaks to get a flat response at expense of THD+N performance.

Best Regards,

  -Diego Meléndez López
   Audio Applications Engineer

Hi Diego,

Many thanks for your reply.

I am first time to evaluate the PCM5242 and DRC feature. Would the DRC of TAS5711 and TLV320AIC3254 are same behavior of DAC output frequency response with peaks?

Our customer has experience using TAS5711 DRC but he found the frequency response is much flat.

With best regards,

Tom

Hi Diego,

I am studying again the PCM5242 DRC Lite feature for customer’s issue as he requires a flatten frequency response. First of all, do you mean the DRC Lite of HF5?

I can’t find HF8 as you mentioned on the PCM5242 Hybridflow Processor User’s guide (slau577a.pdf).

Anyway I tried to verify the HF5 DRC Lite and found abnormal frequency response with very high distortion. Could you please let me know any template of HP5 DRC lite configuration? Many thanks.

The following is my test result.

1. Output frequency response

2. Output THD in FFT view (sine wave 1kHz / -20dBFS; high harmonics at 13.8kHz and 15.8kHz)

Test condition: PCM5242 EVM, PSIA input LRCLK=44.1kHz, MCLK=22.5792MHz, MCLK/LRCLK ratio = 512

Thanks and best regards,

Tom

Hi, Tom,

The response obtained is caused by the different sample rate used in terms of the digital filter used. The HybridFlow 5 is configured for 192KHz operation , so you need to change the PSIA settings to 192KHz sample rate to make it work as expected. 

Best Regards,

  -Diego Meléndez López
   Audio Applications Engineer

Hi Diego,

Many thanks for your reply. I have verified the HF5 DRC Lite with 192kHz sample rate. It works fine with flatten frequency response.

Best regards,

Tom