Combination of two signals with different sample rates

Hello,

I want to combine two signals with different sampling rate. I have have 2 sound signals, one (A) has telephone quality (Fs = 8Kz) and the other (B) music CD quality(Fs = 44.1 KHz). I want to add the music from file B to file A as a music investment (need someweakening). The duration of the result is equal to the longer of A and B.

How i can manage it??

[Mathieu NOE]

hello

1 / resample the 8 kHz signal to the 44.1 kHz (can easily be done with interp1 or resample)

2/ add / mix the two signals but make first sure that they have both same length before mixing the two (with appropriate amplitude ratios). this may require to zero padd the shorter file

[Sotiris Katsimentes]

clc; clear all; close all;

[y1,fs1]=audioread('myone.mp3')

[y2,fs2]=audioread('8kulaw.wav')

sound(y1,fs1);

sound(y2,fs2);

ny1=length(y1);

ny2=length(y2);

N=min(ny1,ny2);

A=y1(1:N);

B=y2(1:N);

signal=A+B;

sound(signal,44100);

Is that wright??

[Jeffrey Clark]

@Sotiris Katsimentes, what @Mathieu NOE provided is not what you did; you missed the resample step, where he indicated changing the 8kHz sample to be 44.1kHz before adding (e.g., y2 from the audioread will be "stretched" to be 44.1 / 8 times its read length). In addition your question seemed to indicated you actually wanted the 44.1kHz sample to be reduced to 8kHz. I don't have the Signal Processing Toolbox where resample is, which may do a fair job of this as well. Bare in mind that if you are not combining two single tones the frequencies, amount of harmonics, chirp, amplitude envelopes, duration, etc. of the several and simultaneous components when converted to the other sample rate may not generate a desireable result without more work.

[Star Strider]

Do not resample the signal with the lower sampling frequency to the higher sampling frequency, because that creates data where none previously existed. Instead, resample the signal with the higher sampling frequency to the lower sampling frequency.

[Mathieu NOE]

hmmm

that depends if the signal sampled at 44.1 kHz should not be downsampled because it contains valuable info in the high frequency range ( 4 to 22 kHz)

beside that , upsampling does not create "noticable" / bad info's if it's done correctly :

• for real time upsampling : insert zero elements AND then low pass filter (see for example : slidesSampling.dvi (toronto.edu)
• for non real time upsampling : you can do the same , or simply interpolation. A higher order interpolation will almost create zero artifacts / info in the "new" frequency range. You can try it , do the upsampling and make the fft of the upsampled signal vs the original signal. You will end up will a almost zero fft amplitude in the extended frequency range. BTW, interp1 does not require any toolbox.

Answer 1

[Peter Perkins]

Use a timetable, and call synchronize. synchronize uses interp1, but it may be that you particularly want to use the SP-oriented resample function instead:

ttHighFreq.yUpsampled = resample(ttLowFreq.y,...)